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

29 November 2008

BOBGRAM7 issued 30 Nov 2008

WEATHERGRAM
YOTREPS
Issued 30 Nov 2008
Bob McDavitt's ideas for sailing around the South Pacific.

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

TROPICS
South Pacific Convergence Zone SPCZ has had a quiet time recently---
some strong convection near Marquesas and with an upper trough crossing
Tonga, but otherwise quiet.

SPCZ is likely to be active in the zone from Northern Cooks to
in-between Marquesas and the main part of French Polynesia and to move
south this week.

Indications are that the SPCZ may slowly pick up in activity between
Solomons and Fiji during the coming week.

In particular a tropical Low with slack winds near its centre is likely
to form over Northern Cooks on 1-2 Dec and then drift west and south,
crossing Niue and Tonga on 3-4-5 December and then maybe deepen over
Kermadecs on 6-7 Dec. Slack winds near the centre but there should be a
squash zone of enhanced easterly winds on the south side of this low---
worth avoiding--- this squash zone is expected to reach its peak near
Kermadecs/Minerva between 5 and 8 Dec.

Not much expected on western side of this low, but be on squall watch
when on its eastern side

SUBTROPICS
Upper air flow around the planet has set up long roller coasters that
are encouraging higher than normal pressures in the subtropics between
120 and 180 W and lower than normal pressures in the Tasman Sea area.

TASMAN SEA/NZ

Fronts and lows are growing well when crossing the Tasman Sea, then
fading as they cross NZ.

On Mon 1 Dec a Low should cross the South Island, followed by a westerly
flow on Tuesday.

On Thursday a front should cross Tasman Sea/NZ, proceeded by a NW on
Wednesday, and then followed by a SW flow and a brief ridge on Fri.

A similar pattern repeats on 6-7-8 Dec, but with a bigger ridge.

So it is a bit like a trampoline in the Tasman this week, try and jump
in rhythm with the weather.


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 November 2008

BOBGRAM7 issued 23 Nov 2008

WEATHERGRAM
YOTREPS
Issued 23 Nov 2008
Bob McDavitt's ideas for sailing around the South Pacific.

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

Well, the troughs in the Hot Aussie interior DID make their stormy way
across Brisbane early last week and have formed a front and Low in mid
Tasman Sea.
The HIGH that crossed NZ has formed a reliable wind at last for yachts
heading from Tonga to NZ and it arrive on Wed 19 as picked in the last
Weathergram. Good to sea the weather unravel according to plan.

TROPICS
The trough moving from central Aussie to central Tasman Sea has turned
the winds in the Coral Sea to a NW flow. It will take all week for the
trade winds to return there. And maybe that's it for the strong trade
winds that have been bothering the Coral Sea over the last few months.
This transition is something look a seasonal transition... it has
allowed westerly winds and thunderstorms to reach Darwin--- the start of
the wet season perhaps. .. There is now a Madden Julian Oscillation
occurring over Indonesia along with some equatorial westerly winds
around Papua New Guinea. This should all drift east and we can expect a
boost in the activity of the South Pacific Convergence zone (SPCZ)
between around 10 to 20 Dec, increasing the chances of a Tropical
Cyclone in the South Pacific around mid December.

South Pacific convergence Zone SPCZ remains in a zone from Solomons to
Wallis/Futuna to Northern Tonga/Niue. Another smaller zone extends from
Tuvalu to Northern cooks. The computer models are indicating that the
SPCZ may shift south and west towards Fiji by the weekend of 29 to 30
Nov. Rain rather than wind, but there may be a small squash zone around
Minerva / Kermadecs late in the month.


SUBTROPICS
High is expected to linger to east of North Island until Tue 25 Nov.
Then a blocking High settles near 40S to south of French Polynesia for
the rest of the week--- there will be a squash zone of easterly winds
along 20S between French Polynesia to Niue for much of the week, good
for sailing west.

TASMAN SEA/NZ
That Tasman Low and its frontal systems is crossing NZ early in the
week, but fading as it encounters the lingering High. Nothing major for
anyone sailing to Opua, but remember to allow for the post-frontal SW
flow on Tuesday.

Next High should bud over southern Tasman Sea on Wednesday and then move
Northeast to north of NZ on Friday.

Next trough should bring a southerly buster to Sydney on Friday and
deepen rapidly into a LOW in South Tasman Sea on Sat 29 Nov then cross
southern NZ on Sun 30 Nov. Avoid.

Weather is looking settled for the CANANZ Boat Show open day at X Marina
at Westhaven in Auckland 0900-1500 Sunday 30 Dec - free entry, BBQ and
prizes, open to anyone (in Auckland) - ask for me.

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

16 November 2008

BOBGRAM7 issued 16 Nov 2008

WEATHERGRAM
YOTREPS
Issued 16 Nov 2008
Bob McDavitt's ideas for sailing around the South Pacific.

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

TROPICS
Some near equatorial westerly winds are appearing in the Indian Ocean
around 5 degrees north-It is too early to tell if this will produce an
east-ward moving surge of activity known as a Madden Julian Oscillation
(MJO)-might do, in which case we will need to watch the Coral Sea
closely in 4 or 5 weeks from now, just before Christmas, for possible TC
activity.

South Pacific convergence Zone SPCZ has reformed in a zone from Solomons
to Wallis/Futuna to Samoa/Northern Tonga. There is still an upper
trough lingering along 25S between NZ and Fiji/ Tonga, with light and
variable winds at sea level to north of this and a band of strong SE
winds on its southern side.

SUBTROPICS
A reliable SE wind is expected to arrive at Minerva on wed 19 Nov and at
Tongatapu on wed/thu 19/20 Nov, good for sailing with to NZ. This
sailing window is brought about by a HIGH crossing NZ on Thu 20 and then
lingering for almost a week just east of NZ. This is the best looking
window we have had so far this month for Tonga to Opua travellers.

TASMAN SEA/NZ
Front is weakening and expected to cross Northland on Monday 17 Nov,
followed by a day or so of southerly winds. Then the weather turns into
a HIGH followed by LOW, with the HIGH crossing the Tasman Sea on 17-19
Nov (good for those sailing from New Caledonia to Brisbane), NZ on Thu
20th, then lingering east of NZ along 40S maintaining a squash zone near
30S.

Large LOW is forecast to form over Victoria and New South Wales on
Wednesday (avoid) and then split into multiple centres as it crosses the
Tasman Sea and southern NZ on Thu to Monday (avoid). The W to SW winds
following the fronts of these lows should reach Northland around Mon
/Tue 24/25 Nov (these can be used for sailing, with care).

The HIGH following this Low is forecast to collapse in the Tasman Sea,
paving the way for another family of LOWS to form in the hot Aussie
interior early next week. This all means unsettled weather in the
Tasman Sea from wed 19 November for maybe 10 days.

I am in Greymouth this week attending MetSoc/hydro Soc conference. Had
scallops and whitebait, followed by a mushroomed T bone and washed down
with Monteiths this evening. Will be back checking email from Sat 22
Nov

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

08 November 2008

BOBGRAM7 issued 9 Nov 2008

WEATHERGRAM
YOTREPS
Issued 9 Nov 2008
Bob McDavitt's ideas for sailing around the South Pacific.

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

TROPICS
Monsoon looks less active than last week but did produce a TC MYSAK.
There is no sign of any equatorial westerlies and no sign of a Madden
Julian Oscillation so looking like it will be a few weeks, maybe more
than a month before we start seeing cyclone activity in this part of the
world. Wow, TC Paloma moving in from the south onto Cuba shows there
is plenty of energy available over there.

South Pacific convergence Zone SPCZ has cleared away from Coral Sea
during past week and is now weak from Tuvalu to Samoa to Northern Cooks.
The active thundery area which visited Fiji Wednesday and Tonga /Minerva
/Kermadecs over past few days and is now over the Niue area is really
caused by an upper trough sitting on top of the tropical easterlies.
This bunch of cold air aloft is confirmed by the hail and whirlwinds in
the showers that visited Fiji last Wednesday. And that's why the winds
have been so slack south of Fiji/Tonga and NZ last week. Anyway the
upper trough has "eaten downwards" and formed a slack surface low near
Kermadecs as picked in the last Weathergram. Yippee, it is good to see
the physics working-we had a lot of cold air flood over NZ last week and
its arrival in the subtropics threw the global weather models in a tizzy
for a few days - their grip on the real world seems to have returned
now.


SUBTROPICS
There is a slack variable flow between Fiji /Tonga and NZ with the
subtropical ridge now shifted to around 40S.
Another upper trough is likely to form another slack surface low near
Lord Howe Island on the front passing the area Sunday/Monday. This will
stall the front so that it sits between New Caledonia and Queensland for
the remainder of the week, fading away. That Low near Kermadecs has a
squash zone between it and the intense subtropical ridge that is near
40S. This squash zone is near 30S and reaches a peak on Monday,
probably worth avoiding unless you like roller coasters Between the
Kermadecs and Lord Howe Lows is a zone of light winds for much of this
week.

HEADING FOR NZ
Front in the Tasman Sea today Sunday is expected to fade over the South
Island on Monday, allowing a new HIGH to form in the central and
southern Tasman Sea on Tuesday and this crosses central NZ on Thursday.

Next front should have more penetration, getting across Northland late
16 or early 17 Nov. Avoid arriving in Opua with or just after this
front. At this stage 18 to 22 Nov are all looking OK days for making
landfall--- try and arrange to go thru this front when it is at 30S ,
say on 17-18 Nov or soon after. From those dates and your vessel speed
you can work out when it may be best to depart Fiji or Tonga or Minerva.
Looks like a breeze good enough for sailing should return to these
places around Wednesday 12 or Thursday 13 Nov, maybe - but the lights
winds on the way will mean some motoring.

I am attending to a MetService display at the Royal Show from Tue 11 to
Fri 14 inclusive, so unavailable this week. Will check email on Sat 15,
then unavailable again from Sunday 16 to Friday 21 Nov, attending a
conference in Greymouth, back on deck Sat 22 Nov. So happy sailing
while I'm away.

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

02 November 2008

BOBGRAM7 issued 2 Nov 2008

WEATHERGRAM
YOTREPS
Issued 2 Nov 2008
Bob McDavitt's ideas for sailing around the South Pacific.

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

TROPICS
Monsoon over Indonesia and Philippines is starting to drift southwards
towards the equator, but the wet season is yet to reach Darwin. There
is a Madden Julian Oscillation occurring - or, in other words, an
increase in showery activity is meandering along the Intertropical
Convergence Zone from Indonesian eastwards. This is happening mainly
along the latitude of 5 North, but I expecting an increase in activity
over Papua New Guinea/ Coral Sea area during the next few weeks - so
this could be an area to be watchful.

South Pacific convergence Zone SPCZ is in a position further south and
west than normal and has been stretching across Vanuatu to south of Fiji
to the Kermadecs area. Another branch extends along 10S from Solomons
to Tuvalu /Tokelau and occasionally visiting Northern Cooks and
Marquesas.

SUBTROPICS

The western branch of the SPCZ is clearing itself at present, but a
jetstream + tropical moisture are feeding an upper trough that has been
lingering over the Minerva /Kermadecs region. This may trigger a slack
surface low over Kermadecs on Tuesday that will move SE and fade away on
Wednesday.

--- Hey, this system will reconfigure the subtropical ridge around about
and kill the trade winds from Southern Cooks to Fiji from Tue to
Friday--- so it is a week of light winds between Tonga/Fiji and New
Zealand. OK for sailing but it will require some motoring through areas
of slack wind.


TASMAN SEA / NZ AREA
Weak ridge starts the week in the Tasman Sea.

A trough crosses the Tasman Sea on Monday and NZ on Tuesday, avoid -it
is followed by heavy swells that reach a peak in the Tasman Sea on
Thursday, avoid.

Wednesday and Thursday -- a westerly flow.

Friday: a Low is likely to cross central NZ; it may deepen over Chathams
but will be weak over northern NZ.

On Saturday a LOW is expected to deepen in the South Tasman Sea and then
weaken as it crosses the North Island followed quickly by a ridge. This
low is worth avoiding in the Tasman Sea BUT shouldn't pose much of
problem for anyone approaching Northland... in fact the northerly flow
ahead of it will help anyone arriving Sunday/Monday 9/10 Nov. Enjoy
watchfully.

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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