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

14 July 2012

BOBGRAM issued 15 July 2012

Issued 15 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 has stopped dropping in the past week. Its 30-day running mean feel during June to a low of -1.21 on 7 July, and recovered to -0.71 by 14 July.

Indian Monsoon covered the entire sub-continent and surrounding seas by 11 July, and is now racing across Malaysia and Singapore. It looks normal at present—there was some flooding last week in South China but unsure if that was related to Monsoon.

In the South Pacific, the Convergence Zone SPCZ continues to be active between Solomons and Tokelau. There was also some activity across Samoa and the Cooks last week and this seems to have been absorbed by the low that is today near 24S165W or south of the Cooks. This low is expected to wander off to the SE and its associated SPCZ linked-trough should cross French Polynesia early next week Mon/Tue 23/24 July.

A convergence zone or trough is likely to move south across Vanuatu and Fiji from Fri 20 July to Monday 23 July- this trough should cross the Tonga area on Tuesday 24 to Thursday 26 July.

Apart from erratic winds and tropical squalls near convergence zones described above, the remainder of the tropics should just have average trade winds this week, good for Island-jumping westwards.

The next STR high is moving off Australia and into the central Tasman Sea on Monday/Tuesday 16/17 July and southeast-wards across central NZ on Wednesday 18 July. It is then expected to move east away from NZ dipping to 45S and then heading for 40S.

NZ/Tasman Sea troughs
Trough that is crossing North Island on Monday should be followed by clearing weather on Tuesday. A new Low is expected to deepen and stall in the central Tasman from Thursday 19 to Sunday 22 July. Avoid. This maintains a northerly flow over NZ until the front arrives on Mon 23 July.

Traveling between NZ and the tropics:
Tuesday 17 July is the best day for departure from northern NZ this week.
Wednesday is second best and the other days are worse.

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