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

03 June 2012

BOBGRAM issued 3 June 2012

Issued 3 June 2012
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.

The Southern Oscillation Index or SOI has relaxed to near zero. It fell to -0.14 on 27 May and was -0.1 on 3 June.

Indian Monsoon seems to be running on schedule and is lapping onto southern India this week.

In the South Pacific, the Convergence Zone SPCZ is active across Solomons to near Tuvalu, and a second branch is sitting from East of Samoa to around the Southern Cooks. On around Tue 5 June a Low is expected to form on the end of the convergence zone to southeast of the Southern Cooks. This low should then move southeast to the south of French Polynesia. This should drag the SPCZ across French Polynesia and turn the winds there from NE to light-and-squally and then to moderate SE. Anyone doing the Marquesas-to-Tuamotu trip should take this into account.
The western branch of the SPCZ is likely to move south across Vanuatu during Sat/ Sun 9 / 10 June and onto Fiji on 11 June.

High that is east of the North Island tonight should wander east and northeast and end the week south of the cooks at around 30S.
Next high is likely to move for Aussie Bight onto New South Wales on Sat 9 June.

NZ /Tasman Sea troughs
Between those two Highs there is room for a trough to open outwards across the Tasman Sea and for a series of lows in the Southern Ocean to extend polar-chilled winds and bursts of swell onto the Tasman/NZ area.

Front is expected to cross the Northland area on Tuesday and a secondary Low that forms on it should cross central NZ.
A stronger front, marking the apex of the upper trough, should cross the area north of New Zealand on Wednesday.
One burst of polar-chilled SW wind and heavy swell from the Southern Ocean is likely to reach southern NZ on Tuesday and another on Thursday, hanging around until Saturday. Avoid.
The primary Low, now deepening off Sydney, is expected to go NE – it is caught on the west side of the upper trough and so has SW winds as its steering field. It should go all the way NE to New Caledonia by the weekend, but weaken into a slack zone after Thursday.

Departing from NZ for the tropics:
Probably a good idea to let those fronts go first. Wind and weather should settle during Thursday and so Friday or later may be the best departure days this week.

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