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Bob McDavitt's ideas for sailing weather around the South pacific

25 December 2010

BOBGRAM6 issued 26 Dec 2010

WEATHERGRAM
YOTREPS
Issued 26 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over past 30 days is
2.3 (an increase of 0.15 in the past week). Oceanic Nino Index for
Sep-Oct-Nov is -1.4

TROPICS
South Pacific Convergence Zone SPCZ is in its normal location for this
time of the year, stretching across the Solomons to east of Vanuatu,
moving north and south over the Fiji/Samoa/Tonga area, then weak between
the Northern and Southern Cooks, and then reasonably active again along
south end of French Polynesia.

A Madden Julian Oscillation MJO of extra convection is appearing over
the Coral sea ... it has already activated things as shown by the brief
appearance of TC TASHA that got to gale force before making landfall
near Cairns on Christmas Eve and then fragmenting inland over Queensland
on Christmas day. Models are producing differing scenarios for where
the next cyclone may form - and maybe not much is likely to happen this
week, except for a tropical low possibly forming near Northern cooks
around Fri 31 Dec and heading for Southern Cooks around sat 1 Jan UTC.
However the chances of formation of a low in the Coral sea are
increasing and GFS is currently producing something there by 4Jan -
EC is as well, but not so intense.

Subtropical jet is conveying the moisture fields from Queensland to NZ
when it gets a chance - when frontal zones allow this --- as is expected
on Mon/Tues 27/28 Dec. Avoid.

SUBTROPICAL RIDGE: STR.
High crossing Tasman Sea and central NZ on Tue/wed 28/29 dec, and next
one is likely from Fri 31 dec to Mon/Tue 3/4 Jan, followed by a strong
northerly flow

TASMAN SEA/ NZ AREA
Front crossing NZ tonight and Mon/early Tues 27/28 Dec is being assisted
by sub-tropical jet. Avoid.

Next trough, on late wed/thu 29/30 Dec, may have separate parts - one
over southern South Island and t'other over northern North island and
should just be a transitional trough between highs.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

18 December 2010

BOBGRAM7 issued 19 Dec 2010

WEATHERGRAM
YOTREPS
Issued 19 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA is still strong. Average atmospheric SOI over past 30 days is
2.05 (a drop of 0.05 in the past week). Oceanic Nino Index for
Sep-Oct-Nov is -1.4

TROPICS
South Pacific Convergence Zone SPCZ is in its normal location for this
time of the year, stretching across the Solomons to east of Vanuatu,
moving north and south over the Fiji/Samoa/Tonga area, then weak between
the Northern and Southern Cooks, and then reasonably active again along
south end of French Polynesia. There is a Madden Julian Oscillation MJO
of extra convection making its way eastwards across northern Australia
but weakening. This should wander into the Coral Sea during the coming
week. However, the accompanying equatorial westerly winds so far have
only reached 130E and computer models suggest that they may not be able
to get east of Papua New Guinea during the coming week. So, therefore,
then, there's a slightly increased risk of cyclone development in the
Coral Sea this week, but computers are not picking developments in this
region.

That low centre off the west coast of Australia has sea surface
temperatures around it that are rated to be below the threshold for TC
development. It should slowly wander west and turn into a trough. Of
more interest is what might happen in the Timor and Arafura Seas as the
MJO passes by. Some models are at this stage producing output showing a
TC around Darwin near Christmas Day (shades of Tracy 1974, I can still
remember), but details are all over the place, and the EC model is not
picking any development --- so if that's near you seek updates.

SUBTROPICAL RIDGE: STR.
High to southeast of Chatham Islands is quasi-stationary and should just
slowly wander north from 45S to 30S by Friday 24 Dec and then fade away.


The next high is expected to be able to get from Australia Bight across
Tasmania around Friday 24 Dec and then cross NZ around Sat 25
Dec/Christmas Day and then move quickly off to the east along 40S on
Boxing Day.

TASMAN SEA/ NZ AREA
There is a long wave trough over the Tasman Sea area helping convey
water-vapour from Indonesia, across Australia, to the NZ area. So this
is likely to be a week with three fronts.

The first went across today Sunday, bringing decent rain to the North
Island. The second is likely to be associated with a tight-centred low
tonight forming off the New South Wales Coast ... wind and rain mainly
for South Island on Tuesday, and then weakening over North Island on
Wednesday and Thursday.
The third front should mark the end of this series and lead in a SW
change (a heralding angel for the Christmas Day high), and should cross
the South Island during the day on Friday 24 Dec/Christmas eve, then the
North island that evening.

A note for those planning to sail from Auckland to Bay of Islands for
the holidays - SW winds for this are likely to be few and far between
during next few months, and this SW may only last for the 25th - light
northerlies returning as soon as Boxing Day afternoon.

SYDNEY-HOBART
Still somewhat uncertain, and depends on whether the Timor and Arafura
Seas can produce a tropical low for Christmas or not. At this stage the
idea is that a trough is likely to wander off the New South Wales Coast
around Boxing day, followed by a period of moderate southerly winds
that back to be from east and then northeast by Tuesday 28 Dec.

Check out moonrise on Tuesday 21st (if sky is clear). It is a full moon
right on the solstice and that does not happen often. It will also be a
total lunar eclipse--- the moon will rise into the earth's shadow and
appear red/brown-coloured, so may be particularly memorable.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

11 December 2010

BOBGRAM7 issued Sun 12 Dec 2010

WEATHERGRAM
YOTREPS
Issued 12 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated. Oceanic Index

La NINA: Still strong. Average atmospheric SOI over past 30 days is 2.10
(a rise of 0.41 in the past week). Oceanic Nino Index for Sep-Oct-Nov is
-1.4 and steady.

TROPICS
South Pacific Convergence Zone SPCZ returned to normal last week, draped
across the Coral Sea and Vanuatu with build ups over Fiji and Samoa. And
there is scattered activity along 15S to French Polynesia FP.

A aging low centre near 25S 170E (to SE of New Caledonia) has a
circulation that is drawing SPCZ activity southwards across Fiji and
Tonga. This centre is expected to fade as it wanders southwards
towards Norfolk Island, and SPCZ activity should continue to hug 15S
this week.

There is a Madden Julian Oscillation MJO of enhanced convection making
its way across the Timor Sea this week and into the Coral sea between 15
and 20 Dec. This should activate the SPCZ. Normally it increases the
risk of cyclone formation, but this MJO is likely to lack a zone of
equatorial westerlies so may not have much impact in the Coral Sea.

Some models are picking that a zone of weak equatorial westerlies may
trigger a tropical low or two to form off NW Australia. The latest GFS
model is picking one to form in Gulf of Carpentaria between Tuesday 14
and Friday 17 Dec and for this to then move SW then S inland towards
Alice as a wet Monsoon Low. In any event an Australian conveyor belt of
upward motion is being set up in the heat trough from North Australia to
Queensland, sometimes reaching Tasman Sea and then onto New Zealand, and
this NW flow in the upper air is likely to last for the next fortnight.

SUBTROPICAL RIDGE: STR.
The STR was knocked north last week but a weak Polar outbreak (polar
index went negative). Southern lows took the opportunity to expand
northwards and one passed by close to NZ - It is now near 45S 165W and
it seems destined to deepen as it wanders north getting as far north as
40S 150W by Wed 15 Dec then exiting to the southeast. Associated High
is making its way east along 30S. Another high is forming just east of
New Zealand tonight Sun 12 Dec. This should wander along 45S on Mon 13
Dec the slide around south-side of that low, but leave a cell near 30S
so that enhanced trade winds are expected all week from FP to Tonga.

Another High is expected to cross NZ Wed /Thu 15/16 Dec and then blossom
east of NZ and slowly shift north to 35S by Tue 21 Dec.

TASMAN SEA/ NZ AREA
Some more southern lows are likely to get near NZ this week. One is
expected to pass by south of Macquarie Island tonight Sun 12 Dec and an
associated front is expected to swipe by NZ on Monday/Tue 13/14 Dec,
followed by a showery southerly change.

A small low may form in the Australian conveyor belt off Queensland
around Wed 15 dec and bring some welcome rain to northern NZ in a NE
flow around Thursday 16/Friday 17 Dec. This may start a trend.

Then another southern low should pass south of Tasmania around Sat 18
Dec as an accompanying low may form off Sydney, feeding from the
activity in the Australian conveyor belt. These lows may dance around
each other around Sun 19 Dec, whizzing close by Southland and blasting a
strong northerly flow across most of NZ. Avoid. Its frontal band is
then expected to cross NZ on Monday-Tuesday 20-21 Dec.

Keep an eye on that conveyor belt as it is likely to continue producing
Lows in eastern Aussie seaboard to NZ area from 23 to 27 Dec, and this
may have an impact of the Sydney-Hobart.
The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

04 December 2010

BOBGRAM7 issued 5 Dec 2010

WEATHERGRAM
YOTREPS
Issued 5 December 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA: Average atmospheric SOI over past 30 days is 1.69, up a bit
from 1.5 last week.

TROPICS
South Pacific Convergence Zone SPCZ had a week off in the Coral Sea as
all that activity hat was over Fiji last week went across Tonga/Niue and
to south of Kermadecs. The remainder of this is expected to fade and
wander off to east on Mon/Tue 6/7 Dec.

A burst of convection occurred along the Queensland coast over the past
few days, but this is already fading and should be gone by end on Monday
6 dec.

A new SPCZ is likely to form over north Coral Sea this week and wander
south to be from Vanuatu to Fiji by 11/12 Dec. Enhanced convection
along this SPCZ is likely from 15 to 20 Dec due to an incoming Madden
Julian Oscillation--- more about that in next weathergram.

SUBTROPICAL RIDGE: STR.
High near Northland on Mon 6 Dec should fade away on Tues 7 Dec.
High crossing South Tasman Sea on Tue 7 Dec should expand to NE by Fri
10 Dec and then expand as it wanders east along 35S, making a squash
zone of enhanced trade winds on its northern side.

NZ/Australia AREA
Trough between the highs may bring showers- one of these troughs crosses
NZ on Mon 6/ Tues 7 Dec bringing a southwesterly change.

The next moves off Sydney on Thu 9 Dec, onto Brisbane and Southland on
Fri 10 Dec, central Tasman and central NZ on Sat 11 Dec, and then onto
North Island around Sun 12 Dec. By then there may not be much left in
this front, so it shouldn't put anyone off trying to approach Northland
from the north.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

27 November 2010

BOBGRAM7 issued 28 Nov 2010

WEATHERGRAM
YOTREPS
Issued 28 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

La NINA: Southern Oscillation Index SOI over past 30 days has eased
from 1.9 to 1.5 standard deviations. The La Nina shows itself on our
weather maps with subtropical ridge being more south than normal in the
Pacific.

TROPICS
South Pacific Convergence Zone SPCZ has been active across northern
Coral Sea to Fiji and, in a more scattered fashion, from Samoa to French
Polynesia.

Moisture within the SPCZ has converged to produce a double-barrelled low
pressure system between Vanuatu and Fiji. The centre of this depression
has been moving east southeast onto Fiji, and may be named as a tropical
cyclone soon.

It has a squash zone of enhanced easterly winds on its south side that
are now around gale force. Some computers are picking that this system
should soon curve off to the south and maybe do a little loop between 25
and 30S near the 180 anti-meridian between Wed 1 and Sat 4 Dec, and then
fade and go off to the southeast.

Anyone intending to sail towards NZ this week should wait for this
system and its swells to move off first.

There was a burst of wet-season-weather on the Queensland coast around
20-22 Nov. There is some rain inland within the Australian heat trough
today and some of this may reach the Cairns Coast on 3 to 4 Dec.

A new Madden Julian Oscillation of enhanced convection is starting to
show signs of possibly reaching the Coral Sea around 10-20 December.
There is no sign yet of any equatorial westerly winds --- these usually
appear in December and can be associated with cyclone development.

SUBTROPICAL RIDGE: STR.
High over NZ today 28 Nov is expected to fade to east of NZ during
Mon/Tue 29/30 Nov.
New high moving over Tasmania at present should slowly cross South
Tasman Sea and South Island 29 Nov to 1 Dec. Then one centre may stall
in Tasman Sea and fade away Sun 5 Dec, and the other move along 40 South
to east of NZ.

NZ AREA
It's another week of high and dry (with some exceptions).

East to southeast flow is likely for Northland, between the low to north
and high to south, from Tue 30 Nov to Sat 4 Dec.

Brief troughs are likely between those highs--- one should bring a NW
flow to the South Island on Mon 29 Nov and SW on Tues 30 Nov. The next
should bring a southerly change from sat 4 to Mon 6 Dec.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

20 November 2010

BOBGRAM7 issued 21 Nov 2010

WEATHERGRAM
YOTREPS
Issued 21 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence Zone has been active across northern Coral Sea
to the Wallis/Futuna area and then stretching off to the southeast of
Tonga. A small tropical low near Wallis/Futuna tonight should fade on
Monday, broadening the trough over and to south of Tonga.

When the cold Southerly winds that are crossing New Zealand tonight
reach this trough over the Kermadecs on Wed 24 Nov --- this is
expected to promote a rapidly deepening and slowly-south-moving Low from
Thursday 25 to Sat 27 Nov--- making for strong southerlies between NZ
and Tonga from 22 to 26 Nov.

So, those staying in Tonga waiting for a comfortable sail to NZ should
keep waiting - may be a brief window around 27-29Nov, but please
recheck.

There's a new branch of the SPCZ budding off the Queensland Coast.
Since we are in the early part of the Cyclone season and have a strong
La Nina, it is to be expected that the SPCZ will spend much of its time
in the Coral Sea, so we can expect this new branch to activate over the
Coral Sea this week, lowering the pressure there. And since there's a
High stalled in the Tasman Sea, the result is a squash zone of enhanced
SE winds along 20 to 25 S this week, especially over New Caledonia.

Computers are picking that tropical Low should form on this SPCZ in
eastern Coral Sea around Wed 24 Nov and this should then deepen as it
crosses Vanuatu on Fri 26/Sat 27 Nov and weaken to south of Fiji by
Tuesday 30 Nov. Avoid this Low and, if in Noumea, consider waiting out
this squash zone.


SUBTROPICAL RIDGE: STR.
That large High stationed at 35S to South of French Polynesia should go
off to 40South and fade away by Wed 24 Nov.

A new high is filling the Tasman Sea during Monday 22 Nov. This should
hold itself there until it fades on Sat 27 Nov... and it should also
squirt a ridge across central NZ and Chathams Islands by Wed 24 Nov that
should go east around the south side of the Low near Kermadecs.


NZ AREA
Cool SW flow over NZ tonight (touch of snow in the Alps) turning
southerly on Monday 22 Nov.

The Stalled Tasman High keeps surrounding features away from NZ this
week, but a trough should be in place over Southland by the weekend in
readiness to move onto NZ early next week when the High fades.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

13 November 2010

BOBGRAM7 issued 14 Nov 2010

WEATHERGRAM
YOTREPS
Issued 14 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS Low 1006 hPa or less near 16S 176E or over NW Fiji this evening
Sun 14 Nov is moving SSE and should then move S then SW and fade near
Norfolk island from Tue 16 to Thu 18 Nov. Avoid the strong winds on
south side of this low and squally showers on its South and Southeast
sides. This means it is not the best week to sail from New Caledonia
to NZ.

The South Pacific Convergence Zone SPCZ has a branch from that LOW that
stretches off to the SE over Southern Tonga: this is weakening but
should wander east across Niue on Tue 16 Nov and Southern cooks on Wed
17 Nov. Another branch is building from east of Solomons towards Tuvalu
along 6 to 9S - this should gradually extend to Samoa and to Southern
Cooks during the coming week, with a drop in pressure. There is
another active branch north of French Polynesia FP between 11 and 17 S,
and models expect this to fade.

Coral Sea may turn into a breeding ground around 23 to 27 Nov.

SUBTROPICAL RIDGE: STR.
HIGH is expected to wander east over north of North Island on Mon 15 Nov
and then off to the east along 35 to 40S from Tue 16 to Sat 20 Nov when
it gets south of FP. There is likely to be a squash zone of enhanced
easterly winds along the north side of this High along 20 to 25S.

The SW flow that swiped over NZ today 14 Nov is likely to be injected
into the back of a trough south of Southern Cooks by Tue 16 Nov helping
intensify a LOW near 35S 155W that may then go through a rapid deepening
process and it shoots off to the SE.
Next High should wander east along 35S across the Tasman Sea slowly from
Fri 19 to Wed 24 Nov, and also have a squash zone of enhanced easterly
winds on its northern side over New Caledonia.

NZ AREA
A trough (the one that upset Tasmanian grand prix today) is expected to
stall over southern NZ on Mon/Tue/Wed 15/16/17 Nov making for a strong W
to NW flow over central and southern areas, and light winds for
Northland. Then a broad trough is expected to cross NZ slowly from
Friday 19 to Sun 21 Nov.

SAILING TO NZ -
SPCZ squalls and rough seas over southern Fiji and just south of Tonga
tonight and Monday.
Winds over Northland should be a useful NE to N from Thu 18 to Sat 20
Nov, then that weekend trough is likely to swing to wind to a SW/S from
Sun 21 to Wed 24 Nov -nothing major, but sailors may need to work out a
waypoint that positions them Ok for those SW winds early next week.

The HIGH SEAS email link I gave last week has suffered link rot. You
can get MetService HIGH SEA warnings via email to query@saildocs.com, no
subject needed, with message SEND
http://m.metservice.com/warnings/marine Or, for latest BRETT coastal,
SEND http://m.metservice.com/marine/coastal/brett.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

06 November 2010

BOBGRAM7 issued 7 Nov 2010

WEATHERGRAM
YOTREPS
Issued 7 November 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The South Pacific Convergence Zone SPCZ is reasonably active and rather
scattered across the Coral Sea, but has weakened east of the dateline
(after being active there last week). During the coming week it looks as
though the SPCZ may weaken in the Coral Sea. A new zone may intensify
in the region from Solomons/northern Vanuatu to Samoa, then move south
towards Fiji and Tonga between 15 and 18 Nov. Be Aware.

A LOW in the subtropics developed near Raoul Island yesterday (Sat 6
Nov) and is moving slowly south along 165W ---it will generate big 3
metre plus SE swells and throw these onto the area between Tonga and
NZ, mainly around Raoul Island, until 13 Nov. This Low will block a
high in the Tasman Sea....

SUBTROPICAL RIDGE: STR.
HIGH is moving to east of NZ along 45S, but is expected to leave behind
a cell that will stall in the Tasman Sea, west of North island. This
stalled high cell will slowly wander to the north and is expected to
finally move east along 35S next week 15 to 18 Nov. There will be a
squash zone of enhanced SE winds on the north side of this HIGH, mainly
between 20 and 25S, from around southern Tonga to west of New
Caledonia, from 8 to 13 Nov ... but the winds near Minerva are likely to
be more from the South until 12th Nov.

NZ AREA
When the stalled HIGH left behind in the Tasman Sea wanders north from
wed 10 Nov, a NW flow should become established over the South Island...
wet for Southern Alps and warm dry winds for eastern South Island. All
OK.


TASMAN SEA
Next major trough should wander from Aussie Bight onto Tasmania on Sat
13 Nov with a low that should swing by Southland by Sun 14 Nov.

SAILING TO NZ???
The squash zone between 20 and 25S, and the southerly wind and 3 metre
plus SE swell near Minerva and Kermadecs, are the challenges.
Winds near Northland are OK: expected to be SE 15 kt or less until wed
10 Nov then SW/W around 10 kt until Wed 17 Nov.

I will be UNAVAILABLE during 8-12 Nov. So, if you want an update for
your arrival, maybe it's a good idea to avoid arriving on those days.
You can get the regular HIGH SEAS forecasts via email to
query@saildocs.com, no subject needed, with message SEND
http://bit.ly/subtropic. Or, for latest BRETT coastal, SEND
http://m.metservice.com/marine/coastal/brett.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

31 October 2010

BOBGRAM7 issued 31 Oct 2010

WEATHERGRAM
YOTREPS
Issued 31 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Welcome to the official start of the South pacific Cyclone Season.
Nothing expected this week. The South Pacific Convergence Zone SPCZ has
been going through an active period recently. It has cleared off Coral
Sea and New Caledonia but is still being strengthened by an upper trough
near Vanuatu and lies almost west-east between 12 and 15S from Rotuma
across Samoa and to Suwarrow, it then extends SE across Southern Cooks.
The upper trough is expected to cross Fiji on Mon 1 / Tue 2 Nov where it
may form a surface low for a time, and then it should weak and it moves
over Tong on Wed 3 Nov. This will likely encourage the SPCZ to come
southwards this week.

SUBTROPICAL RIDGE: STR.
We did indeed get a High well over 1044 east of NZ this weekend. It is
now weakening and migrating NE to east of NZ and that area should become
more zonal and high index by the end of this week with just a ridge left
over along 30S and a disturbed westerly flow further south.

The next High is wandering along 45S across the Australian Bight. Its
nose end is shovelling cold air north, but the showers are expected to
mostly clear in time for the Melbourne Cup on Tuesday. Anyway, this
High should edge NE wards, crossing Tasmania / 40s on Fri 5 Nov, and
tonguing itself onto North island /35S on the 6-7Nov Weekend, then
dividing into two parts on 8-9 Nov - one part moving off to east of NZ
along 40S, and the other stalled in central Tasman Sea at 35S. There
are squash zones of enhanced easterly winds on the north side of this
high.

NZ AREA
Between those highs, there is a replacement trough. This is currently
over Tasmania and, at present, includes a rapidly intensifying low
centre that is rushing off to the South. It's the same trough which
deluged the Melbourne derby yesterday. Anyway it is expected to cross
NZ on Thu 4 Nov, preceded by a strong NW flow over central and southern
areas, and followed by a crisp cool SW with showers that will last into
the start of the fireworks on Fri 5 Nov.

TASMAN SEA
As indicated in my previous weathergram, on 5 Nov a LOW is expected to
form off Queensland coast, it should move SE and deepen, reaching peak
intensity SW of Norfolk on 7 Nov, and then it should slow down and
wobble near Northland on 8-9 Nov - then wander to the east to north of
NZ by around 10 Nov (uncertain). Strong squash zone of enhanced winds
between this LOW and that HIGH to the South especially from 9 to 12 Nov.

SAILING TO NZ???
The High east of NZ will maintain an easterly flow until 4 Nov.
That trough crossing Northland on 5 Nov is followed by a period of SW
winds, but for yachts coming from Fiji or Tonga these winds will likely
only briefly get to 30S and so are just a minor irritation (they will
also bring SW swell - reducing the comfort factor).

Of more interest is that LOW from the Queensland Coast. The computer
models are not yet is agreement as to what it may do, so updates will be
needed. Avoid this LOW neat Norfolk especially on 6-7 Nov as that's
likely to be when it peaks.

As for the Northland coast; most likely (not yet certain) idea is that
LOW will bring a period of enhanced ENE on Mon Tue 8-9 Nov and then
enhanced SE to S winds on 10-11-12 Nov. This complicates all voyages
that may be planning to arrive in NZ in the period from 9 to 12 NOV.
The impact of this Low should clear away so that a new weather window
may start opening for good voyage from New Caledonia /Fiji/ Tonga to NZ
after 13th Nov.

A further complication is that I will be UNAVAILABLE during 9-12 Nov, as
I'll be attending to a MetService display at the Canterbury Show. So,
if you want an update for your arrival, maybe it's a good idea to avoid
arriving on those days.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

24 October 2010

BOBGRAM7 issued 24 Oct 2010

WEATHERGRAM
YOTREPS
Issued 24 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

When the moon fades into its last quarter there may be a rising of
Pololo (or, in Fijian, Balolo). These coral worms choose this time of
the year to spawn. Ask the locals about them, may be fun to watch and
perhaps catch and cook.

LA NINA and the coming cyclone season
First, a recap on our weather zones: The weather engine starts with
energy from the sun. The warmest seas are near the equator and sun on
them causes evaporation which rises to form the Intertropical
convergence zone. Air rises as far as the tropopause and then travels
pole-wards. In the southern hemisphere a lot of this air sinks around
30S and returns along the surface as trade winds back to the equator---
this is the Hadley cell. The zone of sinking air is called the
subtropical ridge. Further south are the westerly winds of the roaring
40s. These weather zones move about, causing seasons. By the time we
get to the longest day, around 22 Dec, the subtropical ridge is usually
"following the sun" southwards and gets to around 40S. This is all part
of the annual cycle.

The second strongest cycle for seasonal weather is the ENSO = El Nino
Southern Oscillation (there are others). When the seas along the
equatorial Pacific Ocean are cooler than normal, as the are now, we call
it a La Nina episode. The weather engine turns over more slowly. The
peak upward motions in the Pacific occur over the Australian side rather
than the Peru side. This has the impact of, in the Southern Hemisphere,
encouraging the weather zones to go further south than normal. Already
the "anticyclones of summer" are reaching northern NZ, and there are
signs of an early start to the wet season in northern Australia. This
also tugs the South Pacific Convergence zone SPCZ to the south and west.

When we look at the sea surface temps, the Oceanic Nino Index ONI for
Sep was -1.0 and when we look at the weather maps the SOI (Tahiti to
Darwin normalised pressure difference) was +2.5. Both these point to a
La Nina that is already moderate to strong. The sub-surface temps in
the central Pacific are cool as well, so the consensus is that this La
Nina will continue through the coming South Pacific Cyclone centre.

NIWA has been able to come up with 8 similar cyclone seasons: Nov 1970
to April 1971 or 70/71, also 71/72, 73/74,75/76, 88/89, 98/99, 99/00,
and 07/08. Using these years as a guide, the forecast for the Nov 2010
to April 2011 season is for 9 to 12 named storms (9 is average). 3 are
forecast to reach at least category 3, and 1 is forecast to reach at
least category 4 (average winds near centre of 64 knots or more). The
Coral Sea and surrounding places west of 180 have an elevated risk of
Cyclone impact.

Although there appears to be a reduced risk for places east of 180, all
communities should remain alert and prepared. In the 8 similar seasons
chosen there have been some cyclone impact in southwest parts of French
Polynesia and in the Southern Cooks. During previous moderate to strong
La Nina's, cyclones have been able to leave the tropics and cross the
Tasman Sea onto southern NZ.

TROPICS (this week)
South Pacific Convergence zone SPCZ is rather spread out, active, and
wide, from the Solomons to Fiji to Northern Tonga and then stretches
southeast across Southern Cooks. There is an active upper trough just
NW of New Caledonia tonight Sun 24 oct. This should cross New Caledonia
on Mon 25 Oct, southern Vanuatu on Tue 26 oct, and then Fiji and Tonga
on Tue/Wed 26 and 27 Oct. Another upper trough is being picked by the
GFS model to cross New Caledonia on Sat/Sun 30/31 Oct. Avoid.

SUBTROPICAL RIDGE: STR.
On Mon 25 Oct a new, replacement, HIGH is expected to develop over NZ as
the older one wanders off to NE and fades away. This new High then
should migrate east along 40 to 45S--- that's further south than normal,
but there will still be an zone of enhanced trade winds on its northern
side - a weak squash zone-- mainly between Fiji/Tonga and NZ from around
27 Oct to 1 Nov. This will provide spirited and bumpy reaching
conditions.

NZ AREA
Another replacement trough is expected to travel NE across NZ on
wed-Fri, 27-28-29 Oct , stalling awhile over central North Island ...
light winds and showery. This should be followed by an intense high
migrating east along 50S, making for a broad zone of easterly flow
between tropics and NZ, that then rotates into a northerly flow in the
Tasman Sea. This is called low-index*.

SAILING TO NZ
Conditions are OK this week, if you are happy with the enhanced trade
winds on the way and if you dodge the squalls of the SPCZ and its
passing upper troughs. Too early to say much about next week yet,
but the weather pattern does seem to be becoming so much of a "low
index" that the next likely step may well be a deepening low in area
south of New Caledonia in first week of November. So it may be better
to leave early rather than linger.

* The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

18 October 2010

BOBGRAM7 issued 18 oct 2010

WEATHERGRAM
YOTREPS
Issued 18 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.
I'm back in the office now from attending to a display for MetService at
the Waikato Boat Show over the weekend, but had to wait until tonight to
get any spare time to write this.

LA NINA
SOI (90 day) is now 2.2 and reasonably steady. This is a strong La
Nina, more than two standard deviations from its mean at present. More
on this in next few weathergrams.

TROPICS
South Pacific Convergence zone SPCZ is now in its normal October
position from Papua New Guinea to northern Vanuatu, then, weak at
present but hovering between Rotuma and Fiji, then move active over
northern Tonga and Niue/Southern Cooks.

An upper trough over South Coral Sea and New Caledonia tonight 18 Oct is
embedded in the upper westerlies rather than the surface trade winds, so
it migrating eastwards... it should activate the SPCZ over Fiji and
Tonga on Tue wed 19-20 Oct. On late wed 20 and during Thu 21 Oct, a
cold southerly / SW wind (from NZ) is likely to reach as far north as
Kermadecs, just as this upper trough reaches the Niue area and this
combination may deepen the pressure around Kermadecs, thus strengthen
the cold winds between NZ and Fiji Tonga for a day or so. Wait for this
to move on before sailing south.

SUBTROPICAL RIDGE: STR.
Remains of last week's BFH are 1028+ at 40S to south of French Polynesia
FP moving off to the east, maintaining good trade winds over FP, much
like last week.

High 1028 is expected to move east along 35S across New South Wales on
19 Oct and then slowly across the Tasman Sea to cross the Auckland area
on Sat 23 Oct, just in time for the NZ Labour Day holiday weekend. Also
in time to impact on this year's Coastal Classic, so that there should
be a good SW wind in Auckland for a spinnaker start on Friday and then a
fading left-turning breeze over night to challenge the heavier boats.
And as that High continue its eastward migration early next week, a
northerly flow is likely on Monday for the boats then returning to
Auckland.

This slow moving high is a good marker for those planning voyages from
Fiji or Tonga to NZ. Wait for that upper trough to pass by, and so
arrange to depart from Fiji on 21 or 22 Oct (or over weekend if you can
get Customs clearance) and arrange to depart from Tonga on 22-23-24-25
Oct period. The High is expected to be over 1030 and east of NZ from
24 Oct and will then have a squash zone of enhanced easterly winds on
its northern side, ending our departure window. With these voyages as
we sail south the high moves off to the east, so we need to time things
OK and arrange to reach Northland before the following trough and its SW
wind change. In this case that trough is likely to be delayed until the
end of the month, say around 30-31 Oct... but it's so far away this will
need to be updated both at the start and during the voyage.

Good voyages from New Caledonia to NZ or Australia are also on the menu
after that upper trough has got east of Noumea, say, around Wed 20
Oct--- there will be some squash zone impact on the north side of the
Tasman High but nothing major.

NZ AREA
There is a strong upper trough and associated thundery cold front
crossing South island on Tuesday 19 Oct and North Island to the
Kermadecs on Wednesday 20 Oct. On Thu 21 Oct, SW winds still likely to
still be strong and showery in the west, but should be easing. From
then on it's the Tasman High that commands proceedings.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

09 October 2010

BOBGRAM7 issued 10 Oct 2010

WEATHERGRAM
YOTREPS
Issued 10 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

LA NINA
SOI (90 day) is now 2.19 and reasonably steady. This is a strong La
Nina, more than two standard deviations from its mean at present. We are
currently investigating analogue years - this investigation is still
being done with NIWA. A classic La Nina shifts the South Pacific
Convergence Zone to south and west of its normal Summer position---
this encourages cyclones in the Coral Sea area. Sea surface
temperatures in there are already warmer than normal, so the season may
start earlier than normal. More on this in next few weathergrams.

TROPICS
South Pacific Convergence Zone SPCZ is now in its normal October
position from Papua New Guinea to Rotuma to Samoa to Southern Cooks.
That surfacing upper trough (SUT) near Niue referred to last week,
managed to work westwards and activate some squalls about Fiji Tonga as
well as Niue over past few days--- First real rain for Fiji for a long
time and I think there may have been some jetstream assistance as well.
Anyway -it hailed in Sigatoka, and that's unusual. Maybe we can call
this an early start to the Fijian wet Season.

Another trough is on the map == this time it's a surface trough that
started off from the mid -latitudes and has been stretched out by a
jetstream between Australia and New Caledonia. It should cross Vanuatu
on Mon Tue 11-12 Oct and then Fiji/Tonga on Wed Thu 13 14 Oct and then
fade.

SUBTROPICAL RIDGE: STR.
Remains of last week's BFH Big Fat High is a centre near 1028+ at 40S to
south of French Polynesia FP moving off to the east, maintaining good
trade winds over FP.
High 1038 in south Tasman sea today near 42 S is shovelling some cold
air onto NZ, and has a squash zone with a little trough on top of it
near Brisbane. High is expected to split into two crossing the South
Island on Tue Wed 12/13 Oct - frosty! The western part should then head
NE for Norfolk and Kermadecs for the 16/17 Oct weekend, and the eastern
part should follow the path of last week's BFH and keep the trade winds
well supported over FP.

NZ AREA
The leading edge of the cold air being shovelled over NZ should cross
North Island tonight (sun 10 Oct). During Mon 11 and Tue 12 Oct the
trough associated with this air is expected to sharpen and form a low
between Northland and Kermadecs. AVOID. This low should then move SE on
Wed Thu 13 14 Oct. There's a ridge over central NZ mid-week and then
over the North island for the weekend. For South and central NZ, a
moist NW flow is expected for the 16 17 weekend.

Heading for NZ? Don't venture south of 25/30S until that LOW had gone
away - say, around Thu 14 Oct. Then try and time arrival to fit in
with a northerly flow over Northland early next week.

NOTE: I'll be unavailable 14 to 17 Oct, busy attending to MetService
display at Waikato Boat Show. So next weathergram may not be until Mon
18 Oct-or later.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

03 October 2010

BOBGRAM7 issued 3 Oct 2010

WEATHERGRAM
YOTREPS
Issued 3 October 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

LA NINA
SOI (90 day) is now 2.15, up 6% from last week, so La Nina is just
getting stronger. It now has values not seen since 1988. NZ's NIWA
Institute will be meeting to consider what this means for the coming
cyclone season, and I shall hold fire with my comments until after that.


TROPICS
South Pacific Convergence zone is mostly found at around 10S, but did
take an excursion across the Coral Sea during last week-touching New
Caledonia briefly.

There is an upper trough over the Suwarrow to Niue area slowly surfacing
to south and east of its axis. It's thundery. Should develop a LOW to
east of the Kermadecs on Mon 4 Oct that will move off to the SE then
stall around Thu 7 Oct.. The tropical extension of the trough will
likely kill the winds over the Cooks this week, and may even turn the
surface winds to a weak westerly, along with cloud and rain. SO it
isn't a good week to "puddle jump" westwards from Tahiti.

SUBTROPICAL RIDGE: STR.
Big Fat High BFH 1038 in mid Tasman Sea tonight 3 Oct is expected to
wander slowly along 40S this week easing to 1030 by the time it gets to
around 170W around Thu 7 Oct, and then slide around the south side of
the LOW that will be blocking its way. Yes there is a squash zone of
enhanced easterly trade winds on the north side of this High. It is, at
present, Sun 3 Oct in the North Tasman sea between 25 and 30S - and
should wander east with the high. It isn't a major, but has been near
gale force about the Whitsundays over past few days.

Next High is not expected to be as intense of the BFH but is likely to
wander east along 35S. It should bud off Australia into the Tasman Sea
around Sat 9 Oct and slide across the north of North island by Wed 13
Oct.

NZ AREA
Between the aforementioned Highs there is to be a passing trough, it
should cross the NZ area on Thu 7 Oct to Sun 10 Oct, preceded by NW
flow, accompanied by a series of fronts and followed by come cool SW
winds. This front is expected to have only minor impact at 30S so it
you are in Fiji or Tonga and wish to sail to NZ and can arrange a voyage
around the back end of the outgoing High, and rendezvous with the front
on 9 Oct near 30 to 35S, then that should be a reasonable voyage to NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

25 September 2010

BOBGRAM 7 issued 26 Sep 2010

WEATHERGRAM
YOTREPS
Issued 26 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

LA NINA
SOI (90 day) is now 2.02, up 9% from last week, now over 2 standard
deviations from its mean so La Nina is just getting stronger.
During October I'll explain what this means for coming migration/
cyclone season.

TROPICS
South Pacific Convergence zone is showing signs of hugging 10S... This
seems to happen around any equinox and so is likely to stay this way a
while. However there are signs of it spreading southwards in the Coral
Sea.

A pulse of extra convection is making its way eastwards from Indonesia /
North Australia into the North Tasman Sea, assisted by a subtropical jet
Stream --- this is producing cloud at high and mid levels and these
should thicken into a surface trough that is likely to cross the North
Tasman Sea on Wed/Thu 29/30 Sep and fade over Kermadecs around Sat/Sun
2/3 Oct.

A similar trough may come and go around Southern Cooks during the week.

SUBTROPICAL RIDGE: STR.
High 1026+ between Northland and Kermadecs at present (26 Sep) is
expected to move slowly SE to 38S and get south of French Polynesia by
the 2/3 Oct weekend and intensify to 1038+. This will strengthen the
trade winds on its northern side into a yucky squash zone. So if you
intend puddle jumping from Tahiti westwards this week, set off early
before the squash zone arrives.

Next High is crossing Australia at present and should move across the
Tasman Sea just as a weak 1025 ridge along 34S from Thu 30 Sep to Sun 2
Oct, and then be reinforced and get to a 1032 Cell and wander along 40S
from 2 to 3 Oct and cross central NZ 3-4 Oct. A welcome change from
past few weeks. Should be good for anyone wanting to come to NZ so long
as you arrange arrival before the next trough strengthens in the Tasman
Sea, and that, at this stage, is looking to be around 7 Oct. Also,
there is likely to be a squash zone building over Tonga/Kermadecs from 3
Oct.


NZ AREA
Monday 27 Sep : NW strengthening
Tuesday 28 Sep : Front embedded in NW flow.
Wednesday 29 Sep : Front stalls over North Island, Low whizzes past
Southland.
Thursday 30 Sep : Front lingers North Island, SW flow establishes
elsewhere.
Friday 1 Oct : Southwest flow ahead of a High.
Saturday 2 Oct : Dying southwest flow ahead of a High.
Sunday 3 Oct: Lighter variable winds around High in central/E
Tasman.
So, at this stage looking OK for the annual CANANZ Kowhai cruise in
Hauraki Gulf.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

19 September 2010

BOBGRAM7 issued 19 sep 2010

WEATHERGRAM
YOTREPS
Issued 19 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

Tonight's write up is a bit later than normal as I'm just now back in Auckland after attending NZ Coastguard national Conference... they are a great bunch indeed!

LA NINA
SOI (90 day) is now 1.85, up 0.11 from last week, so La Nina is just getting stronger.

TROPICS
South Pacific Convergence zone is beginning to return to normal now, showing up and bubbly convection over Papua New Guinea and Coral Sea, and also in an extending line from NW of Samoa across to French Polynesia. It is expected to hold this position this week.

There is a conveyer belt/upper trough over inland Queenstown and this is expected to move out to the Tasman Sea on Mon 20 Sep. It should then fade, but its jetstream is likely to feed some more convection in the Coral Sea, worth avoiding.

SUBTROPICAL RIDGE: STR/ NZ.
It is interesting to note that the parameter I'm using to measure the strength of the Polar Vortex went negative on Thu 16 Sep-That's when the large High I mentioned last week came into play and intensified over the entire Australian Bight. This High also had a Southern Ocean Low to help form an eggbeater onto Tasmania and into the Tasman Sea and onto NZ.

Tasmania took the brunt last Thursday /Friday, then, during the weekend, squally showers brought power cuts to Wellington and Auckland, snow that collapsed roofs in Invercargill, and slips /flooding that caused clusters of road closures. As is the nature of the beast with squalls, not everywhere got hit, and the damaged areas were rather random. Swells in mid Tasman got to an estimated 8 metres last Thursday and peaked on west and south coasts of NZ on Friday night

It's not over yet, there's another couple of shovel-full of cold air for NZ, especially on Tuesday 21 and Wednesday 22 Sep. Another 8 metre burst should roll across southern NZ seas on wed 20 to 22 Sep and reach Chathams around Fri 24 Sep, but the swells in the Tasman Sea are expected to ease to more normal levels by Wed 22 Sep.

That high in the Aussie Bight has not ridged all the way to Antarctic ice-shelf so this isn't a classic polar blast, really it's a wintry entrée to the equinox. Around the equinox, the air along the Antarctic fringe is just starting to get some sunlight after 6 dark months--- it is at the coldest it ever gets , and the sun tends to stir this cold air so that, when encouraged by surrounding pressure systems such as a passing Southern Ocean Low, it gets dislodged northwards. In this case, the shovelling is continuing to be done by that Aussie Bight High.

However, that Aussie Bight high is too far south for the STR at this time of the year--- even in a La Nina year (which twigs the STR to the south), the correct latitide for the STR over Australia around the equinox is about 30-35S , sort of along the South Coast. I think this high got knocked south by that upper trough/conveyer belt that has been over North and Central Aussie over the last few days. SO I agree with the models, and they all take this Aussie Bight high and, slowly, shift it north to 30/35S by Thu 23/Fri 24 Sep so that some high cells ooze across the North Tasman Sea from Thu 23 Sep and over North Island on the 25/26 weekend.

Naturally the strong and sometimes squally westerly winds of the roaring 40s and equinoctial gales will continue unabated to south of this STR line, and reasonably useful trade winds are continuing to north of the STR line.

Taking into account the expecting easing of well in the North Tasman sea by Wed and then the high that is expected to cross the North Tasman and Northland area next weekend, it looks to be a reasonable time to sail to NZ this week.

An added advantage during the next week or so is the full moon. This peaks on Thu 23 sep - and that's the date of this years Sep equinox.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

12 September 2010

BOBGRAM7 ISSUED 12 Sep 2010

WEATHERGRAM
YOTREPS
Issued 12 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

LA NINA
I've been asked to supply some details about the strength of this La Nina... The Oceanic Nino Index ONI, which measures the difference from normal of Sea temperatures in the target area of the eastern equatorial Pacific (Steep) now has a 90 day funning mean of -0.6 == roughly the sea is on average that much cooler than its norm. The Atmospheric Southern Oscillation index SOI, taken from the pressure difference between Tahiti and Darwin, has a 90 day running mean of +1.64 (standard deviations). Both indicate moderate to strong La Nina conditions and the ocean and atmosphere are coupled in this.

TROPICS
South Pacific Convergence zone is beginning to return to normal now , showing up as bubbly convection over Papua New Guinea and Solomons, and as a shear zone of vertical convergence (a layer of trade winds near the surface topped by some vigorous W to SW winds) around Tokelau/Samoa to Tonga/Niue to Southern cooks/ Tuamotu.

The upper trough the marks the boundary of this shear zone is expected to drop to the surface around the Southern cooks/ Tahiti on Tue/Wed 14/15 Sep and then to move south-maybe-Southwest across the Southern Cooks Thu 16 to Sat 18 Sep. Anyone planning the west jump from Tahiti should take this into account - maybe delay a while.

The northern extension of a mid-latitude front that moved off North Island of NZ today is affecting New Caledonia tonight Sun 12 Sep, and should fade away over Kermadecs around Tue/Wed 14/15 Sep.

SUBTROPICAL RIDGE: STR
A BFH big fat high which is well supported aloft continues to dominate proceedings. Its central pressure is around 1038 tonight Sun 12 Sep near 36S 155W and should slowly wander east and ease to be around 1028 at 31S 133W this time next week 19 Sep. So the squash zone of enhanced easterly winds on its northern side is bringing vigorous easterly winds and rough seas between Tahiti and Niue - at least until that trough drops down around Tue 14 Sep, and even after that it will take a while for things to settle down.

Not the best week then for venturing westwards from Tahiti.

Next high cell in the subtropical ridge doesn't have much vertical support - it is budding off eastern Aussie now and will cross the northern Tasman Sea on Mon 13/Tue 14 Sept and fade over Kermadecs on wed 15/Thu 16 Sep.

The high after that is expected to wander east across the Aussie bight along 40/45S on Sat/Sun 18/19 Sep.. shovelling cold air from 55S to Tasmania .. not quite a polar blast but it'll be a wintery entrée to the equinox for SE Aussie.

TASMAN/NZ
A brief break on Monday and then another front on Tuesday 14 Sep UTC, with some heavy rain for western districts, and followed by a cold SW in southern districts.

After another brief break late Wednesday and then some roaring westerlies of spring, enhanced by a deep low in the southern ocean -- these should reach NZ for Thursday 16 and much of Friday 17 Sep, followed by cold SW flow on Sat/Sun 18/19 Sep.

So a voyage from Tonga to NZ departing early this week may encounter a weakening trough/ridge couplet around 30S and then some strong west to SW winds over Northland around 20 Sep, reasonably adventurous.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

05 September 2010

BOBGRAM7 issued 5 sep 2010

WEATHERGRAM
YOTREPS
Issued 05 September 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
There is a strong Walker/Hadley cell combo across the Pacific equator,
with rising air strongest between Malaysia and Taiwan and sinking air
strongest over Fiji to French Polynesia.

The South Pacific Convergence zone SPCZ is looking normal along 10S
across Papua New Guinea/ Solomons, but fades off over Tuvalu and to
north of Samoa. It is expected to extend east at times this week as far
as Suwarrow.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds as far as 15S. One of these
brought some welcome rain to Fiji mid last week (not enough to have much
impact on their dominating dry spell). This has faded somewhat is should
wander east across Southern Cooks on Mon 6 Sep and southern parts of
French Polynesia on Tue 7 and Wed 8 Sep. It is followed by a period of
strong trade winds with a bumpy south to southwest cross-swell. The
next such trough is likely to cross the North Tasman Sea and reach New
Caledonia on Sat 11 Sep.

SUBTROPICAL RIDGE: STR
A big fat high with central pressure over 1030 is moving east along 30S.
It has a squash zone of enhanced trade winds on its northern side over
the next few days. Tonight, Sun 5 sep it is over the dateline.
On Thu 9 Sep it should have wandered east as far as 160W, to south of
Southern Cooks, where it will be reinforced by another High wandering
along 35/40South and the combo high should get to way south of French
Polynesia on the Sat/Sun 11/12 Sep weekend.
Yes, this high is enjoying some of that curtain of sinking air referred
to above in the combo Walker/Hadley cell combo.

TASMAN/NZ
The Tasman Sea/NZ area is slowing moving into a long wave ridge area
after being under the influence of an upper trough for weeks. Even so
there is one more low to come ... This is the one that flooded Victoria
late last week and on Saturday (some places getting heaviest rain in 50
years). Its Northwester and front is crossing most of NZ tonight and on
Mon 6 Sep - heavy rain for Southern Alps and gusty east of the divide.

The low itself should follow and is expected to split into two across
central NZ on Tue 7 Sep--- that will allow a cold southerly to possibly
bring rain/sleet/snow to southern NZ on Monday night to Tuesday night,
and may be some heavy rain to Bay of Plenty during Tuesday.

Thanks to the new long wave ridge, these lows are likely to fade on Wed
8 Sep as a new HIGH crosses southern NZ, but this does bring onshore
flow and rain to eastern North Island.

On Thu/Fri 9/10 Sep, as that new High moves off, a northerly flow is
likely to develop over NZ, but there may be a trough over the North
Island. Then the forecast is for a front on Sat 11 Sep followed by a
westerly flow on Sun 12 Sep. The outlook next week 13-18 Sep is for
West to southwest winds over Northland, so those days may not be good
days for sailing towards NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

29 August 2010

BOBGRAM7 issued 29 Aug 2010

WEATHERGRAM
YOTREPS
Issued 29 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The South Pacific Convergence zone SPCZ is strong along 10S across Papua
New Guinea/ Solomons and Tuvalu, and is likely this coming week to
extend to Tokelau, and maybe even affect Samoa to Suwarrow at times,
but otherwise is weak.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds as far as 15S. One of these is
expected to affect Fiji on Mon 30 Aug (some welcome rain!) Tonga on Tue
31 Aug, and then fade on its way to Southern Cooks by Thu 2 Sep.
Apart from this interruption, it looks to be a good wind for trade
winds in South Pacific.

SUBTROPICAL RIDGE: STR
Something to do with some extra energy in the subtropical jetstream
above around 30S. So the High that is expected to reach Lord Howe Island
by Wed 1 Sep should anchor its stern there and then rapidly extend
eastwards along 25/30S so that its nose gets to south of French
Polynesia by Fri 3 Sep. This is in response to a curtain of sinking
air, and it helps to feed the trade winds at 15 to 20S over the entire
region.

Next HIGH in the Tasman should build east of Sydney around Friday 3 Sep,
in good time to cross the North island during the 4/5 Sep weekend J

TASMAN/NZ

The long wave trough that has been bothering the Tasman sea is
retreating north for a bit. There is still a haphazard procession of
fast moving fronts bothering Tasman /NZ but the distance between troughs
is getting more, allowing for some voyage planning. And there may be a
break in this with next weekend's passing High.

Before then, today's trough is expected to settled into a couplet of
lows east of the North Island on Mon 30 Aug to Wednesday 1 Sep (stand
by for some rain in the Hawke's Bay ranges). The next trough is likely
to be preceded by a vigorous NW wind over South Island on Thu 2 Sep and
followed by a disturbed SW/S flow on Friday 3 Sep.

Anyone intending to head south to NZ this week can probably find
reasonable weather so long as an arrival around 6 or 7 Sep is targeted.
Plenty of south/southwesterly winds for anyone heading North, but avoid
the prefrontal conditions on Thu 2 Sep.

The parameter we use to measure the strength of the polar vortex has
indeed gone negative in the past few days, first time since May. This
increases the chances of a polar outbreak somewhere ... and indeed there
seems to be one near the Horn this weekend, but none, so far, anywhere
else.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

22 August 2010

BOBGRAM7 issued 22 Aug 2010

WEATHERGRAM
YOTREPS
Issued 22 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The South Pacific Convergence zone SPCZ is slowly returning to normal
over Papua New Guinea and Solomons. It is putting in an appearance
around Tokelau, but otherwise is weak . Should continue to rebuild
from Tuvalu to Northern Cooks this week, and may start to drift south
for a while next week.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds as far as 15S over French Polynesia
and as far as 20S elsewhere. One of these is moving east off French
Polynesia today 22 Aug, and another should cross Tonga on 23 Aug, Niue
on 24 Aug, Southern Cooks on 26 Aug, and French Polynesia around 28-30
Aug. SO this week is something like a repeat of last week.

SUBTROPICAL RIDGE: STR
Upper air is such that Subtropical highs are being encouraged in north
Tasman Sea and in the broad zone east of NZ. There is a high cell in the
North Tasman Sea today 22 Aug: it should cross NZ on Tues 24 Aug and
then wander to the east slanting to 35S then 25S and reaching 150W to
South of French Polynesia by Sat 28 Aug. There should be a squash zone
of enhanced trade winds on the northern side of this high.

TASMAN/NZ
Weak frontal system is likely to cross NZ on Wed 25 Aug after that High
- preceded by a northerly flow and followed by a westerly.

A long wave upper trough is hovering around the Tasman Sea again this
week.

At ground level, we have a broad cold trough and a deep southern ocean
Low located today well to south of West Australia at 150E. This system
is the highlight of the coming week. Its Low centre should start moving
NE out of the southern Ocean when it gets south of Tasmania on Wed 25
Aug and reach NZ on Sat/Sun 28/29 Aug. However, there the High
following this system and it is expected to expand at 30 to 35S over SE
Australia on Sat /Sun 28/29 Aug. So that will limit the southerly fetch
this low can draw on, so it'll be wet and windy, but not a polar
outbreak.

SO it is OK to approach NZ until Tue 24 Aug. Then not OK until around 2
Sep.

The strength of the polar vortex was mentioned last week. Well, its
still holding its strength and is not weakening as much as the computer
models have been picking. Even if it does weaken to a stage that a polar
outbreak can occur in early September, the chance that this will impact
on our quarter of the world will be 1 in 4. So, while it is interesting
to watch for, it ISN'T another thing that yachties who are planning a
voyage from tropics to NZ or Australia need to worry about.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

15 August 2010

BOBGRAM7 issued 15 Aug 2010

WEATHERGRAM
YOTREPS
Issued 15 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
The causative factor for the cold air that brought floods to Pakistan
and slips to China AND the hot air bringing heat waves to Russia is the
same: meanderings in the Northern Hemisphere's jet streams. Over the
past few days NZ copped a burst of water vapour that had come from the
monsoon area, and this brought something like 200 to 300mm rain to our
mountains with some flooding and slips most notably around Whakatane,
but some drier air is now separating Asia and South Pacific.

The South Pacific Convergence zone SPCZ has faded recently over Papua
New Guinea and Solomons - should rebuild there by 20 Aug. It has built
up along 10S between Tuvalu and Tokelau, and is likely to slowly spread
south possibly affecting Rotuma to Samoa by Friday 20 Aug.

Passing troughs in the mid-latitudes have been extending sufficiently
northwards to affect the trade winds along 20S. One of these is moving
east off the Tuamotus today 15 Aug, and another should cross Tonga on
16 Aug, Niue on 17 Aug and Southern Cooks on 18 Aug. Then the
subtropical ridge may be strong enough to block any northern extensions
of mid-latitude troughs, for a while anyway.

SUBTROPICAL RIDGE: STR
Small high cell in the north Taman Sea today 15 Aug is expected to move
east along 25S and fade near 180 on Mon 16/ tue 17 Aug. Next High will
be larger, forming in Tasman Sea on Wed 18 Aug and then moving east
along the 25 to 30S latitude band, reaching 180 around Fri 20 Aug, and
likely to be south of French Polynesia around Sun 22 Aug. There should
be a squash zone of enhanced trade winds on the northern side of this
high.

TASMAN/NZ
A long wave upper trough is hovering around the Tasman Sea this week.

At ground level, a broad cold trough, with squally thundery showers, is
now crossing the Tasman Sea and should cross NZ on 16 and 17 Aug.
Its SW flow is likely to linger over NZ on Wed 18 and much of 19 Aug.

Most settled day this week is looking to be Fri 20 Aug - for anyone
contemplating sailing to or from NZ.

Another broad cold trough is expected to cross Tasmania around Thu 19
Aug and reach the South Island on Sat/Sun 21/22 Aug.

There is a parameter that measures the strength of the polar vortex
(that ring of westerlies than encircles Antarctica). It is called the
AAO and can ne seen at
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/
aao_index.html
- and known locally as SAM (Southern annular modulus).
Not usually relevant here, but has been way out of whack recently with
record high values, up to 4 standard deviations from its mean last
month. This suggests that Antarctica's cold air has recently all been
locked up, no polar outbreaks anywhere. Well, computer modelling is
suggesting this will all change by end of August, and then polar
outbreaks will be on the menu again (not sure which longitude band yet).
--


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

07 August 2010

BOBGRAM7 issued 8 Aug 2010

WEATHERGRAM
YOTREPS
Issued 8 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
More heavy rain is forecast in the Monsoon over Pakistan this week, and
lots of rain over much of Indonesia. A conveyor belt directed some
moisture from there to NZ over the past few days. If you have access to
Internet see this at http://www.ssec.wisc.edu/data/comp/wv/wvmoll.mpg

The South Pacific Convergence zone SPCZ is strong about the Solomons and
somewhat quiet elsewhere. It is expected this week to build in the
Tuvalu and Tokelau area, and this may spread towards Samoa by the end of
the week.

Passing troughs in the mid-latitudes are extending far enough northwards
to affect the southern parts of the tropical South pacific, but not to
reach the SPCZ. One of these is located south of Fiji tonight and
should wander east and reach Southern Cooks by Thu 12 Aug UTC...
Preceded by a swing of the trade winds so they come from the NE,
accompanied by some squally rain, and followed by southerly winds and
clearing weather. Another of these troughs is expected to form off the
east coast of Queensland on Tue 10 Aug and wander east across the Coral
Sea to reach New Caledonia by Thu 12 Aug. If sailing, try and plan
around these troughs - at least remember that the computers and GRIB
data can not resolve the details near them.

SUBTROPICAL RIDGE: STR
Long wave pattern continues to be conducive to forming troughs in the
Tasman Sea and helping the STR in longitudes east of the dateline.

The HIGH forming now/8 Aug UTC over western Tasman Sea is expected to be
rather slow and weak until it crosses northern NZ on Wed 11 Aug and then
should expand east of NZ until Sat 14 Aug. There is likely to be a
zone of enhanced trade winds on its northern side.

TASMAN/NZ
A southerly start to the week with an outgoing low- barometers are
rising. Rain was briefly intense on Saturday and there are still some
intense showers around- in Wellington slips are disrupting traffic.

Fronts following Wednesday's high are likely to cross NZ on Thu 12 and
Fri 13 Aug, followed by a low that may linger over Northland for the
14/15 weekend.

So it is OK to sail towards Northland if you can get there by
Wednesday, and anyone planning departure should consider waiting until
next week.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

01 August 2010

BOBGRAM7 issued 1 Aug 2010

WEATHERGRAM
YOTREPS
Issued 1 August 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
Asia is much wetter than normal, and in true Walker circulation style
this extra rising air is producing more sinking air in the subtropics,
accentuating the subtropical ridge especially around the eastern Indian
Ocean and Western Australia.

The South Pacific Convergence zone SPCZ has been knocked a little south
by this so that it has been DRY recently over Vanuatu, Fiji, and from
Samoa to Tahiti, and wetter than normal from Coral Sea to south of Niue,
with trade winds much stronger than normal over the whole South Pacific,
especially about Coral Sea where it is being drawn into a strong
Monsoon.

A passing upper trough in the mid-latitudes is likely to help accentuate
the SPCZ between Samoa and Southern Cooks on 2 Aug (UTC). There should
be some squally showers in this trough as it crosses Southern Cooks
around 3 Aug and Tuamotus by Thu 5 Aug. This offers something for the
puddle jumpers at Tahiti to take into account.

SUBTROPICAL RIDGE: STR
Long wave pattern is conducive to forming troughs in the west Tasman Sea
and helping the STR in longitudes east of the dateline.

The Large HIGH over 1036 east of NZ today (1 Aug) is expected to wander
east along about 40S this week, with a Low forming on its northwest
shoulder near 30S 150W around Tue 3 Aug UTC. As this pair wanders off to
the east, some smaller High cells are likely to form near latitude 30S
about and east of NZ by Fri 6 Aug, with fresh to strong trade winds on
their northern side.

TASMAN/NZ
One Low deepened in the mid Tasman Sea on 31 July and is expected to
track SE across Southland tonight. Next Low should deepen off New South
Wales on Mon 2, rotate clockwise around the Tasman Sea and weaken into a
trough that is likely to cross NZ on Wed 4 Aug UTC. Third Low should
deepen rapidly over Tasmania on Wed 4 Aug and rotate clockwise around
the Tasman Sea and cross North Island around Sat/Sun 7/8 Aug UTC.

There are brief ridges with slack winds between these lows but generally
too brief to allow much planning for a sail trip to or from NZ.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

24 July 2010

BOBGRAM7 issued 25 July 2010

WEATHERGRAM
YOTREPS
Issued 25 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence zone SPCZ is mainly along 8 to 11 South from
Solomons to Tuvalu/Tokelau. It occasionally peels away to the southeast
and makes a trough-an example of this should occur over Tonga Niue on
Sat 31 July, and this may develop into a LOW to south of Southern Cooks
early next week.

Passing mid-latitude trough occasional extend north in to the tropics.
As they pass, the trade winds weaken and get swung to be from the NE for
a while, then squalls appear, sometimes followed by a swing to southerly
winds. One of these events is near Niue tonight and should wander east
across Sothern Cooks by Tue 27 July.

SUBTROPICAL RIDGE: STR
This is stronger than normal now and further south than normal, signs of
an incoming La Nina.

HIGH 1034 budding off New South Wales on Mon 26 July should wander along
35S crossing northern North Island around Thu 29 July and reaching 150W
by Sun 1 August. A Squash Zone of enhanced trade winds is likely on
north side of the High, mainly between 15 and 10S, reaching Samoa on
Tuesday/wed 27-28 July. This squash zone is especially strong in mid
Coral Sea and across northern Vanuatu until Wed 28 July. Avoid.

TASMAN/NZ
With the incoming High, NZ is in a disturbed West to Southwest wind
flow, with fronts, on Monday/Wednesday 26-28 July; OK to good for
sailing off to the north.

After the Thursday HIGH, a disturbed flow from the NW is to be expected
over NZ, and this should wetten the West Coast and warm the East Coast,
and lead to a LOW crossing the South Island on the 31/1 weekend; good
for sailing towards Northland from the tropics, but please note this
good window closes quickly by Sun 31 July.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

18 July 2010

BOBGRAM7 issued 18 July

WEATHERGRAM
YOTREPS
Issued 18 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence zone SPCZ is showing signs of drifting south
after a few weeks of hovering along 10S to 14S. One branch extends from
Solomons to Wallis/Futuna, and another branch is hovering between 10 and
14S between Tokelau and Samoa and around Northern cooks.

The SPCZ is occasionally enticed southeastwards to merge with
mid-latitude troughs. As this combination wanders east along around 20S
it swings and then kills the trade winds for a day or so, but that's
about all this week.

For those in Tahiti looking to go west: One of these troughs is
expected to pass by Rarotonga on Mon 19 July. The next is departing
Queensland at present, should pas by New Caledonia on wed 21 July, Tonga
on Sat 24 July and Rarotonga around Tuesday 27 July. Otherwise this is
a week of trade winds.


SUBTROPICAL RIDGE: STR
A lot can be gleaned by watching the rhythm of the highs as they wander
east in the subtropics. Their shifting isobars mould the troughs
inbetween them.
This week the STR is becoming better defined in the pacific than it has
been for awhile.

One High with central pressure around 1025 is wandering along 30 to 35S
, across Northern North Island on Mon 19 July, then slowly and steadily
east or southeast to get to 40S well to south of French Polynesia around
Friday 23 July. This High is mediocre, so will maintain moderate trade
winds and settled weather in the tropics on its northern side. Good for
sailing to the west.

Next High is likely to be more intense, building to 1035+ between 35 and
40S in South Tasman Sea around Mon 26 July. Too far away to be sure,
but this high is likely to cross central NZ on Wed 28 July and should
have a squash zone of enhanced trade winds on its northern side - and
these strong winds will likely start in Coral Sea from Wed 21 July and
spread east to reach Vanuatu/New Caledonia by weekend of 24/25 July and
further east next week. Be wary.

TASMAN/NZ
It is between the highs that the lows can flourish, scrum together, and
elbow outwards.

There's a trough departing the Australian eastern seaboard tonight (18
July) and as this trough crosses the Tasman Sea on Monday/Tuesday 19/20
July a Low is forecast to form within it. This low will likely have
colder than normal air in its upper parts and that help to deepen its
central pressure, slow it down and breed squally showers/strong
winds/heavy swell. It may deepen to below 995 while still west of the
North Island on Wed 21 July. Avoid. Should then start to weaken , but
may still be around 1000 hPa as it crosses North island on Friday 23
July, and then it should wander off to southeast of NZ and expand to
cover the broad area between the two highs mentioned above.

So anyone sailing to NZ should best arrive by Tue 20 July, and this
isn't the best week to depart NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

11 July 2010

BOBGRAM7 issued 11 July 2010

WEATHERGRAM
YOTREPS
Issued 11 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
South Pacific Convergence zone SPCZ is still quiet but slowly activating
along 10S from Coral Sea, in clumps, all the way to Northern Cooks and
Marquesas. It has been hugging to 10S latitude, but occasionally links
south with mid-latitude fronts, making wet troughs --- one affected the
Cooks on 7 and 8 July and another affected Fiji on 9 and 10 July. This
latter trough is expected to continue eastwards and finally fade out
between Cooks and Marquesas on 15 and 16 July Thu/Fri. Anyone heading
west from Marquesas to the Cooks, or south from Tonga or Fiji to NZ will
need to factor this trough into their plans.

There is a low; lets call it L1, which has formed with the trough that
was over Fiji last night. This Low is near 30S 180 and should move
steadily south along the 180.

Total Eclipse: Clouds seem to be keeping away from the area that will
become a total eclipse at 111830UTC near Maria Island in the Tuamotus
(and Mangia Island in the Southern Cooks). Easter Island is currently
partly cloudy and clearing, but there is a cloak of cloud heading that
way, so fingers crossed there.

SUBTROPICAL RIDGE: STR
High over 1030 crossing NZ this weekend is likely to wander off to the
east between 40 and 45S getting as far east as 140W by the end of this
week. This is so far south that it isn't likely to enhance the trade
winds on its northern side-but there will be a squash zone between it
and L1 that is worth avoiding.

Next high upstream will be slow to appear, and is likely to bulge east
off southern Queensland around Fri/sat 16/17 July, stretching east along
25/30S to get to 180 by Tue 20 July. This northern latitude STR will
help enhance a westerly flow over NZ.

TASMAN/NZ
Yes, we got polar air over NZ this weekend, as mentioned in the previous
weathergram; it was mainly dry but did manage to bring us the lowest
temperatures we have seen this winter.

As L1 comes south over next few days, the eastern North Island are
likely to get a dose of cold southerly rain, especially on Wednesday
/Thursday 14/15 July.. But the low should be further away than last
week's, and hopefully will have less impact.

There are some nice tail winds around L1 for anyone wishing to sail
northwards from Northland. These winds will fade away by Wednesday and
then turn northwest and then strong westerly for the remainder of the
week.

A winter /Southern Ocean Low is expected to deepen off Tasmania on Wed
14 July and then head northeast out of the south Tasman and onto the
South island / central NZ on Sat 17 July, followed by a disturbed
southerly and then a Southwest flow.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

03 July 2010

BOBGRAM7 issued 4 July 2010

WEATHERGRAM
YOTREPS
Issued 4 July 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: It seems this week that the direct route using
the current near 4South is NOT any faster than the alternative route
using the strong west-going current at around 2 degrees North from 100
to 120W. If you do decide to take the northern route you have to get
away for the east-going current at the equator, and you will likely
experience some squally showers.

TROPICS
South Pacific Convergence zone SPCZ is reasonably quiet this week, and
is mainly in the northern Coral Sea and northern Vanuatu and from there
along 10S towards Tokelau and Northern Cooks. There is an interesting
dry slot of sinking air from Fiji to Southern Cooks, and another around
northern Australia.
Due to High pressures that are now blocked over southern Australia there
is a zone of enhanced trade winds in the Western Coral Sea and around
the north end of Queensland. This should ease after 7 July but isn't
going to go away this week.

SUBTROPICAL RIDGE: STR
High to east of NZ today Sun 4 July is set to move steadily along 30S
and fade on 5 July. Another associated High should expand at 45S -50S
and this High fades This High should then move NE and reach 40S to south
of French Polynesia around Fri 9 July, with a squash zone of enhanced
trade winds on its northern side.
Next high upstream is stalled over South Australia but should be able to
send a cell across Tasmania on 8 July, South Tasman Sea on 9 July, and
South Island on 10-11 July.

TASMAN/NZ
This week the NZ region will be dominated by a large slow-moving low.
It isn't expected to ingest any cold polar air until 9 -10 July and by
then should be mostly off to east of NZ. The centre is expected to
track east along 33S to 180 and then southeast, so that most of its wind
and rain should stay out to sea, but Gisborne and Hawke's bay are in for
steady rain from Monday to Wednesday. The SE winds associated with this
low should cover northern NI tonight/Monday and central/southern North
island on Tuesday and Wednesday 6-7 July.

The low should be far enough away to allow reasonable sailing to the
north again by Thu 8 July. There is likely to be a left-over trough
between NZ and Fiji and this may activate early next week, so updates
will be needed.

As for sailing from Tonga to NZ, well : there may be a reasonable voyage
afte the low has gone, starting around 9 July, but you will need to be
prepared to sail through a trough.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

26 June 2010

BOBGRAM7 issued 27 June 2010

WEATHERGRAM
YOTREPS
Issued 27 June 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: trade winds are now strong enough so that boats
faster than 6kt may sail this route directly, hugging 4S as long as
possible. Slower boats and those looking for an alternative route
should get to may between 1 deg and 2deg North of the equator for a free
ride on the equatorial west-going current, especially from 095 to 125W.
No weather to mention, but note that in the Northern hemisphere near
the Americas Cyclone CELIA is still going and Cyclone Darby is about as
well.

TROPICS
South Pacific Convergence zone SPCZ is active along 8 to 10S across the
Solomons area to Tuvalu and Tokelau, and then active again across French
Polynesia. There are occasional bursts of activity occurring about
northern Vanuatu and northern Fiji, but nothing organised.
Due to High pressures that are now blocked over southern Australia there
is a zone of enhanced trade winds in the Western Coral Sea and around
the north end of Queensland. This should ease after 30 June.

SUBTROPICAL RIDGE: STR
Large HIGH over 1030hpa to south of southern cooks / at 160W / is moving
steadily east along 40S. Its associated squash zone of enhanced trade
winds should affect southern parts of French Polynesia this week.

Small HIGH around 1020hPa is moving along 25S and should get from south
of New Caledonia today to south of Niue tomorrow/28 June. Another small
High around 1020hPa is likely between 25 and 30S to south of New
Caledonia on 29 to 30 June , and should then fade.

And the next HIGH is likely to bring a period of light winds across the
central Tasman Sea and NZ building to 1030+ from 5 to 7 July next
week...- a window that motor vessels may use to help cross the ditch as
comfortably as possible (and sailing vessels may wish to avoid).

TASMAN/NZ
This week in the local region we have just two small cells in the STR
around 25/30S, so the whole Taman Sea/NZ /east of the dateline area is
open to having a broad trough.
There should be one front/trough crossing NZ on Monday/Tuesday 28/29
June, followed by a disturbed W/SW flow for the remainder of the week.
After this SW wind change gets to Northland on wed 30 June, there should
be a reasonable window from sailing away from Northland. BUT note that
the frontal trough may deepen into a small low when it is north of NZ
and as it crosses near the Kermadecs on 2-3-4 June-so if heading for
Tonga ensure you go clockwise around it.

These conditions will make sailing TO New Zealand challenging this week.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

20 June 2010

BOBGRAM7 ISSUED 20 June 2010

WEATHERGRAM
YOTREPS
Issued 20 June 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: trade winds are now strong enough so that
anyone sailing this route may as well go direct, rather than chase the
extra help of the west going current that is around 30 miles north of
the equator. Head for 4S and then hug that latitude to 120W - that will
avoid a counter just west of Galapagos and prolong time in a west going
current near 4S. No weather to mention, but note that early this week
there are TWO cyclones in the NE Pacific, BLAS and CELIA.


TROPICS
South Pacific Convergence zone SPCZ is building in activity. It spent
last week over Coral Sea/Vanuatu, Fiji, and Samoa, then weaker between
Northern and Southern cooks, then strong again over French Polynesia FP.
It should reform slightly further north over Tuvalu and Tokelau this
week, and some of the convection in the SPCZ is likely to be drawn to
the SE by passing mid-latitude troughs - so look for troughs turning to
lows in the subtropics at around 20 to 30S from Sat 26 to Sun 27 June:
one near 180 and another near 120W/ SE of FP.


SUBTROPICAL RIDGE: STR
The squash zone and heavy swells over FP on Sun 20 June are related to a
HIGH at 40S, to Southeast of FP. As this wanders off to the east it
will take its squash zone with it.

HIGH crossing Tasmania on Tue 22 June should go east and get across
South Island on wed 24 June and then should slide northeastwards and
reach 30S to south of FP by Monday 28 June. cross the Tasman Sea on
Tue/Wed 15/16 June, and North Island on Wed 16/Thu 17 June, and then
slide off to the NE and get to move smartly along 40S to be south of
French Polynesia by Mon 21 June. Its migration to the east will be
accompanied by a squash zone in the trade winds on its northern side,
mainly along 20S. There will be a squash zone with this High, but
mainly on its NW shoulder.

Next HIGH is likely o be delayed getting across Australia and, at this
stage, is expected to reach Tasmania around 1 July - so next week, with
no Subtropical ridge around NZ, the stage is set for a large LOW over or
east of NZ.

TASMAN/NZ
Disturbed W/SW flow over NZ is good for those wishing to sail off north
today/Monday/Tuesday 21/22 June, but on wed 23 June an SE change is
likely to reach northland. This will be counter productive to sailing
and, combined with the movement of the High to the South Island is
likely to result in the formation of a LOW that may loop and linger
around Northland for the remainder of the week.

The next good sailing window from Northland will then be after this low
has moved sufficiently off to the east - probably Mon or Tue 28/29 June.
And that low is likely to deepen and expand in area as it goes east,
because of the weakness of the STR. If you are interested in this
window, then be aware that it may be bothered by lows and troughs
lingering around 30S, so re-check closer to the time. Also, around 1
July, between the expanding low to the east and the incoming High in the
South Tasman Sea, there should be a polar outbreak with cold
southerlies over NZ.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

13 June 2010

BOBGRAM7 issued 13 June 2010

WEATHERGRAM
YOTREPS
Issued 13 June 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Galapagos to Marquesas: Apparently some are still "puddle jumping"---
There is a good west going current to be found at around 30 miles north
of the equator . Take this to around 123 W and then head direct for
Marquesas. Weather is looking settled this week.

TROPICS
South Pacific Convergence zone SPCZ is active mainly in the Eastern
Coral Sea, with scattered areas along 10S near Tuvalu to Tokelau/Samoa.
This week the convection to north of New Caledonia is expected to drift
east, and form a trough to east of New Caledonia. Around Wed 16 June a
low should start to form in this trough and then deepen and travel SE
to east of North island and South of Kermadecs by Sat 19 June. There
will be a squash zone between this LOW and a HIGH over NZ on 16 -17
June.

Anyone taking the opportunity to sail north from NZ when the SW winds
start easing on Mon 14 June and heading for Fiji or Tonga should ensure
they go clock-wise around this low and its squash zone.

SUBTROPICAL RIDGE: STR
HIGH should cross the Tasman Sea on Tue/Wed 15/16 June, and North Island
on Wed 16/Thu 17 June, and then move smartly along 40S to be south of
French Polynesia by Mon 21 June. Its migration to the east will be
accompanied by a squash zone in the trade winds on its northern side ,
mainly along 20S.
Good to see this pattern return, as it is the regular winter pattern.
That LOW mentioned as forming in the tropics will probably wait for this
High to get out of the way first.

Next HIGH may be delayed and knocked to 45S and move into South Tasman
Sea south of Tasmania on 22 June.

TASMAN/NZ
The arrival of the Wed/Thu High coincides with the start of the National
fieldays which I will be attending this week. Fog and frost will be on
the menu.

A front should cross NZ on Fri 18/sat 19 June following this High, but
this is expected to fade as it comes, so will not bring a SW change to
Northland.

A Low is forecast to form off the Queensland coast on Fri 18 June, and
this should move SE across the North Tasman Sea and then across
Northland around Tue 22 June Tuesday. This LOW may or may not be
able to time its arrival along with the outbreak of cold southerlies
that will be shovelled onto the South Island by the next HIGH. So NZ
may be in for another cold S/SE outbreak early next week.

This means that the NEXT SW wind change in Northland for good sailing
to the North has been delayed to maybe the end of next week /maybe the
end of the month. Tomorrows "window" closes quickly too.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

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