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

01 July 2012

BOBGRAM issued 1 July 2012

Issued 1 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 been steadily dropping into the negative for the past month. It has fallen from -0.14 on 27 May to -1.03 on 1 July.

Indian Monsoon is not progressing well, and is now about 2 weeks late over NW parts of India.

In the South Pacific, the Convergence Zone SPCZ is rebuilding well in the in the Coral Sea region. A bunch of clouds were able to spin around each other on Friday producing 91P, but this was near to an area of strong wind shear so the system lost its top before it could get any traction.

The SPCZ should gradually build and move further south in the Coral Sea this week. The branch of SPCZ that is showing intermittent activity along 10 to 15S across Tuvalu, Tokelau and Northern Cooks should persist this week.

High that has come from the south and is building east of the South Island tonight at 45S is expected to migrate slowly eastwards shunting away that large low on its eastern side Island.
Next large High is currently in the Australian Bight and should wander east across South Australia and New South Wales from Wed 4 to Sat 7 July and the cross the Tasman Sea and NZ next week.

NZ /Tasman Sea troughs
The warming prefrontal NE flow and warm front is spreading over NZ tonight and during Monday. The multi-centred trough that follows is expected to linger until Sat 7 July, followed by a southerly flow from 55S.

Traveling between NZ and the tropics:
Best days to depart from northern NZ this week are when the SW flow arrives and settles down around Sun 7 July.

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