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

22 May 2010

BOBGRAM issued 23 May 2010

WEATHERGRAM
YOTREPS
Issued 23 May 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
Take off to just north of the equator at first, and go to around 125W,
and enjoy a following current and a moderate wind from south or
southeast. Then head direct for your destination and winds should
oblige and be southeast 15 knots. may be some tropical shower activity
around Marquesas this week.

TROPICS
South Pacific Convergence zone SPCZ was very active across Vanuatu/New
Caledonia to South of Fiji/Tonga last few days. A burst of convection
has been captured by northwest winds aloft and is wandering across
Vanuatu today (Sunday) and should then wander to the southeast, getting
to 998 very close to the Kermadecs on Tuesday morning and then fading
and heading south. This is the low that we were picking for the
Auckland to Fiji Yacht race would be at 981 near North Cape on Monday
night and would bring 8 metre + swells to near 30S on Tuesday - under
this new path the swells in that region then will be more like 4 metres.


There is another branch of the SPCZ stretching from Wallis/Futuna to
Tuvalu to Tokelau. This branch is expected to wander southwards across
Fiji on Monday and then across Tonga on Tuesday and Wednesday. Later in
the week a new SPCZ should reform over Papua New Guinea and Solomons.

SUBTROPICAL RIDGE: STR
High 1 has its cell east of New Zealand (we enjoyed it here on
Saturday), and is on its way to the east and should reach French
Polynesia longitudes on Thu/Fri 27/28 UTC with a squash zone of enhanced
trade winds on its northern side.

The STR is weak after that high, as the Tasman Sea turns into a low
breeding ground. High2, a cell east of Tasmania is all that is left in
our part of the STR and it will be forced to wait, and finally squeeze
across to south of NZ on Thu 27 May. For those waiting for the STR to
reassert itself across the Tasman Sea so that they can have a
comfortable voyage from Auckland to the tropics--- indications are, at
this stage, that you may need to wait til early June. I think the STR
tends to fade like this whenever there is a kerfuffle in the Sea Surface
Temperatures around Galapagos.
.

TASMAN/NZ
When the STR is weak the Tasman Sea becomes a low breeding ground. Last
Thursday night's low got to 999 near North Cape.

Low 1 for this week is 1005 in mid Tasman today and should drop to 985
as it crosses Cook Strait on Tuesday/Wed 25/26 May. At its peak on
Wednesday when centred east of Marlborough, there will be squally
westerlies and heavy swell over western NI, but of more importance will
be the squash zone between Low 1 and High 2 (referred to above). This
flow will drive SE winds directly onto the eastern SI, mixing cold and
moisture in a chamber of lowering pressure: a formula good for mountain
snow on the eastern slopes of our Alps.

Low 2 for this week should roll across New South Wales on Tue, be around
1005 near Lord Howe on Wed 26 May, 1001 near Norfolk on Thu 27 May and
1005 near North Cape on Friday 28 May. The squash zone between Low 2
and High2 should bring a large zone of easterly gales onto the eastern
NI during the 29/30 May weekend. This combination will make for a
larger impact that last Thursday's 999 low near North Cape. Avoid.

Low 3 should deepen offshore Sydney on Sat 29 May, making for a real
southerly buster: avoid.

I made a late night typo last week, so here's a correction: Those of
you who have email at sea can download the latest NZ high seas forecast
by sending an email to query@saildocs.com, no subject needed, with
message SEND http://bit.ly/subtropic, as well as listening to it on
ZLM.

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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