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

22 July 2012

BOBGRAM issued 22 July

Issued 22 July 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 continues to relax. Its 30-day running mean fell during June to a low of -1.21 by 7 July, and relaxed back to -0.34 by 21 July.

Monsoon is now moving onto Malaysia and Singapore.

In the South Pacific, the Convergence Zone SPCZ has been active about and east of Solomons, returning some welcome rain to Kiribati. One branch stretches across Vanuatu and Fiji. Another rather broken branch affects parts of Tokelau and Northern Cooks.
During the next week, trade winds are expected to weaken and westerly winds of the mid-latitudes are expected to creep northwards.
On Mon/Tue 23/24 July a combo of the SPCZ and a mid-latitude trough is expected to move from west to east across French Polynesia. This trough is expected to deepen into a low near 30S 125W on Thu 26 Jul, and this low may deepen to 990 and drift south. Avoid.

High east of NZ near 170W tonight is expected to continue to go east-wards between 30 and 35S this week.
High over New South Wales is stalled at present, and rather weak. It is expected to cross the central Tasman Sea on Thursday 26 July and northern NZ on Fri /Sat 27/28 July… then it fades so that there is not much left of the STR by early Aug. This is a sign that the SOI will be dropping again shortly.

NZ/Tasman Sea troughs
Slow-moving Low is expected to drag itself across the North Island on Monday and Tuesday, propelled by the slowly rising pressures in the southern Tasman Sea.
New Low is expected to deepen quickly off Sydney on Fri 27 July and cross NZ of Sun/Mon 29/30 July.

Traveling between NZ and the tropics:
Wednesday 25 July is best day for departure between Lows.

Traveling between New Caledonia and Australia
Going west; well the Tasman Lows over challenges, but Monday to Thursday look OK. Going east; maybe think about departing on or after Friday 27 July rather than before.

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