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

29 May 2010

BOBGRAM7 issued 30 July 2010

Issued 30 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.

TC AGATHA starts off the new North American Cyclone season, rolling into
Guatemala from the Pacific Ocean and its rain is turning ash from a
recent volcanic eruption to some sort of ready mix concrete.
Not much change from last week... 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 at southeast 15 knots.
South Pacific Convergence zone SPCZ, after having most of its energy
taken off into the mid-latitudes last week, is slowly reforming now
along 10S, from Papua New Guinea to east of Solomons to Tuvalu/Tokelau
and extending to Samoa at times.
A combination of clouds from the tropics + jetstream intensification + a
large upper low feeding mid-latitude fronts resulted in a lot of
thunderstorms between Fiji and New Zealand last week, no doubt harassing
the Auckland to Fiji race fleet.
This week a trough is likely to form over Vanuatu on Thu/Fri 3/4 June
and deepen into a low to east of New Caledonia on Sun 6 June. The Low
should then get caught in a jetstream and shoot southeast and deepen
rapidly as it crosses the Kermadecs on Mon 7 June - avoid it then.
The High currently crossing southern NZ should wander along 40/45S
eastwards and get south of French Polynesia mid next week around 10
June. There is a rather mediocre zone of enhanced trade winds on its
northern side.
Next high to wander along the STR should also take the 40S latitude but
is likely to extend eastwards as a tongue rather than as a closed
centre... reaching Bass Strait from Tue 1 June to Thu 3 June and Central
NZ from Friday 4 to Saturday 5 June, just in time for start of NZ
Queen's Birthday holiday weekend.

Between the Highs mentioned above come the lows. Last week's lows took
their time to cross NZ, so that we had an opening gambit of strong NE
winds and rain last Monday, then a middle game as the rain band
spiralling into the centre stalled over South Island, and finally a
squash zone/eggbeater moulded by the low and the incoming High.

The next low has deepened off Sydney on schedule as picked in last
week's weathergram, but isn't as well positioned as last week's low to
develop much further. It will however take its time as it crosses NZ
and split into a multi-centred system on Tues 1 June.

For those waiting in Northland to sail off north, the useful SW winds
should arrive there on Thu 3 June. There may be another front crossing
Northland on Fri 4-Sat 5 June with a change to southerly/southeast
winds. Sun 6 June could be light winds at Northland, and then there
may be Ok winds for sailing north again on Mon/Tue 7/8 June. Enjoy.

The terms used are more fully explained in the METSERVICE Yacht Pack.
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