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

26 February 2011

BOBGRAM7 issued 27 Feb 2011

WEATHERGRAM
YOTREPS
Issued 27 February 2011
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.

That Christchurch quake was devastating. Kiwi people are all one family
and all suffering shock together this week. NZ Govt has set up a fund
to help recovery at christchurchearthquakeappeal.govt.nz

TROPICS
La NINA is still strong, and has strengthened a little in the past week
with its 30day running mean rising from 1.9 on 19th to 2.14 on 26th.

There are falling pressures and persistent convective rain over much of
northern Australia, and this rain is likely to move inland and
southwards this week.

South Pacific Convergence Zone SPCZ was cleaned out when Tropical
Cyclone ATU was vented from the tropics last week. SPCZ is now slowly
redeveloping in the trough left behind, from Solomons to Vanuatu and
then scattered over Fiji and Tonga. East of this zone the flow is
generally from E or NE, and to the west there are light winds over the
Coral Sea.

SUBTROPICAL RIDGE:
HIGH1 is wandering east along 40S to east of NZ and should reach 140W by
5Sat 5 March... the trough on north side of this High is expected to
deepen into a LOW near 30 to 35S around 150 to 160W from Fri 4 March and
there will be a squash zone between this Low and HIGH1. Avoid.

HIGH2 in the Australian Bight is expected to move east across Tasmania
on Sat 5 March, pushing a cold southerly onto NZ on Sat 5 March. This
means there is a long gap between highs over Taman Sea /NZ area and
maybe enough delay so that a LOW may form off Queensland on Fri 4 March
and reach North Island early next week, preventing HIGH2 from getting to
NZ. This scenario may change (read next weathergram).


NZ Area
Weather maps show a trough-troubled week ahead. Low from Tasman Sea is
expected to cross southern NZ on Tuesday 1 March followed by a brief SW
change on Wed 3 March. A much colder front followed by southerly wind
is expected to cross NZ on late Fri 4 March/Sat 5 March, weakening and
stalling over Northland for the weekend. === Another challenging week
for the Round North Island Race fleet


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 February 2011

BOBGRAM7 issued 20 Feb 2011

WEATHERGRAM
YOTREPS
Issued 20 February 2011
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, but weakening. Average atmospheric SOI over 30
days to 19 Feb Jan is 1.9, steady in the past week after dropping 0.5 in
early Feb.

TROPICS
South Pacific Convergence Zone SPCZ spent last week mainly over a wide
altitude zone between 10 and 20 S from Vanuatu to Tonga, with several
regions of tropical downpour. ATU was named near Vanuatu on Saturday. In
Africa (Ghana), the word ATU is occasionally given to a boy born on a
Saturday, so this is seemingly appropriate -however, in Polynesia, ATU
is the Samoan mythical name for the first man to settle in Fiji. The
system is certainly hugging Vanuatu, looking at today's satellite
imagery, may be doing a loop as it slowly re-curves to the south.
Future track is most likely to be south and then southeast--- kicked
along by upper NW winds already in place at 20 to 25S.

ATU is likely to take with it a lot of the energy/activity that is in
the current SPCZ, so it will slowly rebuild after Wednesday along the
trough area that will stay behind over Fiji to Niue. May be OK for some
Island hopping in this hiatus period, but no steady winds.

TC DIANNE off Western Australia is going south and following the Leeuwin
current. It may clip some coastal areas in the process.

King Tides on Sun 20 to Tue 22 Feb, so give these cyclones a wide berth.


SUBTROPICAL RIDGE:
HIGH1 is wandering northeast from 45S 160W to 40S 140W this week, and
maintains a disturbed NE flow on its "back shoulder"(NW quadrant)
HIGH2 starts this week crossing the Aussie Bight and should cross
Tasmania on Friday and then travel northeast across Tasman Sea on Sat 26
Feb and central NZ on Sun 27 Feb.

NZ Area
Transitional trough between HIGH1 and HIGH2 to approach South Island on
Monday (heavy rain tonight in the SW) and cross NZ on Tuesday followed
by a southerly wind change on Wednesday. A challenge for the SIMRAD
Round North Island Fleet sailing counter clockwise from north end to
Wellington, restarting on Tuesday. This trough is expected to linger
off to east of North Island on Thursday as remains of ATU roll SE along
the trough line--- this may throw swells at North Island east coast and
perhaps some rain, but its main wind and rain are likely to be well off
to east. May sideswipe Chathams on Friday.

One more SW to southerly front on Friday, and then clearing weather on
Saturday as HIGH2 arrives. On Sun 27 Feb, there may be a NW flow over
Southland and an easterly surge over Northland/Auckland (just like Wed
16 Feb).


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 February 2011

BOBGRAM7 issued 13 Feb 2011

WEATHERGRAM
YOTREPS
Issued 13 February 2011
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, but weakening Average atmospheric SOI over 30
days to 10 Feb Jan is 1.9, a drop of 0.5 so far this month.

TROPICS
South Pacific Convergence Zone SPCZ is now reforming after being cleared
out by YASI last week. It is mainly between 10 and 15S over western
Coral Sea, with occasional tendrils to New Caledonia, and in an
unorganized zone over Tuvalu to Niue, occasionally extending to Fiji.

This week is likely to be quiet in South Pacific. A LOW may form around
New Caledonia at some stage and go west, but should fade by Friday.
Another LOW may form over southern Tonga area at some stage and then
wander SW to south-of-Fiji then track to southeast on weekend of 19-20
Feb.

The MJO activity is starting again over western side of Australia. TC
BINGIZA is about to make landfall over Madagascar, and computer models
are staring to identify possible tropical lows over Gulf of Carpentaria
or going south and following the Leeuwin current along west coast of
Australia this week.

SUBTROPICAL RIDGE:
Some mobile high cells... HIGH1 is wandering northeast and starts this
week at 1030 hear 45S 160W , maintaining a steady trade wind flow on its
northern side.
HIGH2 starts this week crossing the Aussie Bight and should hug 45S as
it goes east , crossing South Tasman Sea on Tue 15 Feb and moving off to
east of Chathams on Thu/Fri 17/18 Feb. At this stage it looks like it
will be followed by a multiplicity of troughs and fronts over the South
Tasman Sea/South Island area from 19 to 21 Feb.

NZ Area
Transitional front between HIGH1 and HIGH2 is moving east off the South
island tonight.

There is a low near Kermadecs (as there was this time last week) and it
should fade as it comes south, but may edge a little to wets and bring
clouds and showers to Northeastern NZ between Tues and Thu 15 to 17 Feb


Apart from the above, it looks like a typical "La Nina weather week"
for NZ with higher pressure to the south and an easterly flow over the
north. This easterly may weaken over next weekend for the Auckland to
Mangonui leg of this year's SSANZ SIMRAD Round NI race.

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 February 2011

BOBGRAM7 issued 6 Feb 2011

WEATHERGRAM
YOTREPS
Issued 6 Feb 2011
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 30 days to 6 Feb
Jan is \
2.6 (an increase of 0.19 since 22 Jan).

TROPICS
YASI strengthened as it crossed Coral Sea to be Cat 5 when it made
landfall over Queensland-the largest since 1918, devastating. It held
integrity as far as Mt Isa and its moisture caused flash floods over
Melbourne on 5 Feb then dissolved into a trough ahead of which the NW
winds hit 40C in Timaru, NZ, today, Waitangi day. Remarkable.

YASI cleared the Coral sea of its energy, and, according to Australian
academics, has ended this active phase of a Madden Julian Oscillation,
MJO, so that the next phase of cyclones may be with next MJO in March.

However, tropical depressions are still occurring. The one near Raoul
Island should move south and fade away next few days, but may have some
impact in Bay of Plenty/Gisborne around Tues 8 Feb. Avoid.

SUBTROPICAL RIDGE:
Next High is expected to cross Tasmania around 8 Feb and hug 45 S and
cross South Island around 10 Feb, then move off to east of NZ followed
by a NE flow.

NZ Area
The transit of that low from Raoul Island on Tues 8 Feb coincides with a
SW/S change over NZ + some big swells from the Southern Ocean into the
Tasman Sea. Avoid. Next trough should cross Tasmania on Fri 11 Feb and
then southern NZ around 14 Feb.

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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