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

28 June 2008

BOBGRAM7 issued 29 June 2008

WEATHERGRAM
YOTREPS
Issued 29 June 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

Galapagos to Marquesas: just as last week, head direct for 4S 96E then
go straight. This will avoid the strong east-going current and use the
winds best: winds are SE over Galapagos and turn easterly to west of
110E.

TROPICS
The South Pacific Convergence Zone is going thru a quiet time now. It
is still active around northern Coral Sea and has a few flashes of
activity across northern Vanuatu and west of Fiji. There is a weak
branch from Samoa to French Polynesia. A brief burst of heavy rain is
likely Sunday/Monday about and southeast of Kermadecs from a passing
front.

SUBTROPICAL RIDGE
A large HIGH is being calved eastwards from Australia but is likely to
shrink as it crosses the Tasman Sea on Monday and Tuesday however it may
expand again east of the dateline on Thu and south of French Polynesia
on Friday Saturday. This High will enhance the trade winds north of it
as it migrates eastwards. Next HIGH is likely to leave Australia on
Sunday 6 July, and should take a path slightly further south.

Mid Latitudes
Last week brought one northerly front, one thundry then one windy
westerly front, and finally a southerly (with a low). That southerly
will peel off to the east on Monday, and that's when a brief ridge will
bring some frosty sunshine to the South Island. Tuesday's the North
Island's turn for a light-wind/sunny break.

The next broad trough is set to move across Tasman Sea/NZ on Wednesday
to Saturday, with its main front on Thursday, and cold southerlies over
South Island on Friday/North Island on Saturday. Avoid this front.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

21 June 2008

BOBGRAM7 issued 22 June 2008 NZST

WEATHERGRAM
YOTREPS
Issued 22 June 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

Galapagos to Marquesas: head direct for 4S 96W then go straight. This
will avoid the strong east-going current and use the winds best: winds
are SE over Galapagos and turn easterly to west of 110W.

TROPICS
The South Pacific Convergence Zone quietened down last week. There was
some increase in activity over Papua New Guinea but some fading in
activity to north of Fiji. This section is expected to drift south onto
Fiji this week, but should not be as strong as it was earlier this
month. A branch of the SPCZ was almost along the some latitude from
northern Tonga to French Polynesia, and this section is expected to
drift north.

There are strong southeast winds in the Coral Sea, and these are being
maintained by the anticyclone that is stalling over Australia. From New
Caledonia to French Polynesia the subtropical ridge is weak and has been
shoved north to 25S, so the trade winds are also weak in this part of
the tropics.


Mid Latitudes
A real wintry week for NZ.

The trough referred to in the last weathergram has arrived over the
North Island. As it moves off to east of the South Island on Monday,
its southerlies will be cold enough to bring some mountain snow.

A southerly jetstream is starting to show itself over Tasmania at
present and this is expected, late Tuesday, to bring unusually cold
southerly winds from to southern ocean onto NZ--- with squalls and
showery show, and with some dollops to sea level.

In the wake of this, on Wednesday to Friday, it looks like a disturbed
westerly flow with gales and heavy swell in the Tasman Sea. Avoid.

On Saturday a LOW is likely to deepen near Chatham Island, bringing
another southerly to NZ for the weekend. There may also be some
reasonable trips from Northland to Fiji/Tonga departing Wednesday -
these trips will experience some squally westerlies and heavy swell near
North Cape.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

14 June 2008

BOBGRAM7 issued 15 June 2008

WEATHERGRAM
YOTREPS
Issued 15 June 2008
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

I should have mentioned last week that weathergram.blogspot.com is an
ADDITIONAL way to get this weathergram. I'll keep emailing them as
well.

Galapagos to Marquesas: Back to other route this week-head direct for
4S 96E then go straight. This will avoid the strong east-going current
and use the winds best: winds are SE over Galapagos and turn easterly to
west of 110E.

TROPICS
The South Pacific Convergence Zone was active last week- and showing
signs of a pulse of extra convection. It mainly extends from Papua New
Guinea to Solomons to Fiji and then faded further to the southeast. A
trough moving along the SPCZ brought heavy rain to Fiji and this is
finally moving off tonight 15 June. This week the SPCZ is expected to
drift north and should affect Samoa to Southern Cooks/southern French
Polynesia.

Mid Latitudes
Hmm, the trough I was talking about last week to "fade away" on Friday
13th in the Tasman Sea, didn't do that-it stalled and, over the weekend,
has been deepening near Lord Howe Island to below 1000, making a heavy
southerly swell on its western side. Well it is now expected to move
east and fade to north of Northland on Thursday. Its fronts should
attack northern and eastern North Island on Monday and Tuesday. Avoid
these fronts and be mindful of this Low. There is a companion low to
southwest of Fiji tonight - and it should follow those fronts onto
northern Northland and fade away.

That new big-fat-High over Victoria today is expected to spread east and
cross the South Island on Tuesday-Wednesday and to expand as it moves
over Chathams and further east on Thursday-Friday-Saturday. This will
enhance the trade winds between Southern Cooks and Fiji for a few days.
Loos at this stage that a low might form on the northwest shoulder of
this BFH, as they do, and that will be to south of Southern cooks,
taking that squash zone south-wards.

After the BFH, there will be a large trough filling the entire Tasman
Sea next weekend in time for this year's winter solstice, and moving
onto NZ early next week. We will look at that in the next weathergram.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

07 June 2008

BOBGRAM7 issued 8 June 2008

WEATHERGRAM
YOTREPS
Issued 8 June 2008
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

NEWS: I'm now publishing the WEATHERGRAM at
http://weathergram.blogspot.com so if you want one by email send an
email to query@saildocs.com, no subject required, saying SEND
http://weathergram.blogspot.com

Galapagos to Marquesas: New suggested plan: because the winds are
mostly south-south-east around Galapagos to 105W use these to hop north
to the equator and sail westwards along the equator: Avoid the strong
east-going current between Equator and 3 degrees S. Near Equator 105 to
110W head SW - there is less current here - and from 5S 120W to
Marquesas to winds start to turn to be south-easterly.

TROPICS
The South Pacific Convergence Zone was rather quiet over the Coral Sea
recently, and is now slowly returning to that area. It has been more
active than normal over Fiji and in a broad band from there across Tonga
and Niue and parts of the Southern Cooks. This branch of the SPCZ is
forecast to wait for pressures to start falling between Vanuatu and
Fiji, as is likely to happen around Thu 12/Fri 13 June UTC. This
pressure fall is then likely to trigger a rapidly deepening LOW that
will move off to the SE - across the Kermadecs on Sat/Sun 14-15 June
UTC. There will be a squash zone between this low and the High to the
south--- strong enough to generate gale East /NE winds and heavy swells
for a time. Avoid this LOW and its squash zone.

The tropical extension of the trough associated with this low is likely
to reach Tonga on 15 June UTC / Niue on 16 June UTC / and fade over
Southern Cooks on 17-18-19 June UTC , preceded by a weak NE winds,
accompanied by tropical squall and followed by a return to trade winds.

Anyone sailing from French Polynesia westwards will need to sail through
that SPCZ.

Mid Latitudes
The Big Fat High BFH in the Tasman Sea is expected to cross the North
Island on Wednesday - with a squash zone of enhanced trade winds on its
northern side between 170 W and 170E mainly along 20S. When this BFH
moves off to the East on Thursday and Friday it is expected to induce a
fall of pressure on its northwest shoulder-that will be between Vanuatu
and Fiji, triggering the low mentioned above. Avoid this low.

So this BFH turns out to be NOT the best scenario for sailing from NZ to
Fiji or Tonga... but OK for sailing from NZ to New Caledonia or eastern
Australia. The trough following the BFH in the Tasman Sea on 11-12 June
is expected to fade away on 13 June. Not like that trough which brought
heavy rain to Queensland last week.


The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

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