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

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

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