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

14 August 2011

BOBGRAM issued 14 Aug 2011

WEATHERGRAM
YOTREPS
Issued 14 August 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.

TROPICS
Southern Oscillation Index SOI continues to hover in the positive: its 30day running mean was 0.79 on 5 August and 0.87 on 12 August.

South Pacific Convergence Zone SPCZ is steady in the zone from Solomons to Fiji. There is another convergence zone lying from west to east from Tokelau to Northern Cooks sort of along 10S.
That portion of the SPCZ which is over Fiji at present is expected to travel east (the upper winds are westerly), and reach Tonga on Wed 17 Aug UTC and Southern Cooks on Fri 19 Aug UTC and then fade over southern French Polynesia FP this weekend.
The portion of SPCZ near Solomons remains in place and should be able to spread south into Coral Sea by Sat 20 Aug and onto Vanuatu/New Caledonia this weekend.
Maybe some strong SE winds in the western Coral Sea this week.

SUBTROPICAL RIDGE STR
STR is weak over Southwest Pacific at present….a fading high south of FP extends a weak ridge westwards mainly along 25S to south of New Caledonia and then southwards across the Tasman Sea to a high over 1032hPa in the south Tasman sea
--- this Tasman High is centred near 50S at present, shovelling a cold southerly flow onto NZ. It should just slowly wander along 50S to be south of NZ by Thu 18 Aug and then move NE along eastern NZ this weekend and set off to east of North Island along 40S early next week, intensifying to 1038 for a while on Monday 22 August.

TASMAN SEA/NZ AREA
There is a polar blast over NZ today, shepherded by large areas of low pressure to east of the country and that 1032+ high in the south Tasman High. There may be a small low caught in these southerlies and sideswiping the east North Island Coast on Tuesday 16 August UTC intensifying the winds. The polar blast is making for large seas that may peak on Tuesday 16 Aug at around 5m in the eastern Tasman and around 9m between Canterbury and Wairarapa coasts. Avoid.

Southerly winds should turn SE then E and ease, first in the south Wednesday 17 Aug, reaching North Island by Sat 20 Aug.

A new LOW is expected to move across Australia and deepen off its east coast near Sydney on Thu/Fri 18/19 August and then wander to the NE near Lord Howe on Sun 21 Aug and Norfolk around Tue 23 Aug, preceded by an area of strong NE winds. Avoid.

SAILING TO/FROM NORTHERN NZ.
Polar blast winds and sea should ease enough for OK sailing from Northland on Thursday/Friday…after that the NE winds of the next Low may interfere.

It isn't really the right weather for coming south but if you intend to, then Friday/Saturday are looking OK weather for arrival days.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

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