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

12 February 2012

BOBGRAM issued 12 Feb 2012

Issued 12 February 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.
La Nina's indicator in the atmosphere, the Southern Oscillation Index, is hovering around 1 (moderate). It was 0.79 on 5th February and 1.07 on 11th Feb.

The MJO cycle of enhanced convection peaked over the past fortnight and is now relaxing. At its peak TC CYRIL formed and moved off toe the southeast of Tonga. TC JASMINE formed in the Coral Sea and managed to skirt around the Loyalty Islands then south and southeast to be now near and SW of Minerva. It has managed to cocoon its own blob of tropical air to work with, even though it is now in sea surface temperatures not quite warm enough to continue it. So it is weakening, but will take a while yet to spin down. It is expected to be deflected north back into the tropics, to west of Tongatapu by Wednesday and then to weaken and go southeast. Avoid Minerva.

The South Pacific Convergence zone SPCZ remains active from Papua New Guinea to Solomons to Fiji/Tonga then to the southeast. The moisture of TC JASMINE has broken away from the SPCZ and is doing its own thing. A low is expected to form on the SPCZ to SW of Southern Cooks on Monday and then move off to the southeast Another Low is likely to form in the Coral Sea on Mon 20 Feb but is expected to move off to the SE too quickly to deepen any further. The next MJO cycle (and enhanced risk of cyclone formation) is now expected to be mid-to-late March. HOWEVER, Tropical cyclones may form between MJO episodes so take care if planning a tropical dash.

A weak STR is in the Tasman Sea today and exerting a ridge across southern South Island towards Chathams. This STR is likely to be disrupted by a trough over next few days… one lobe may reform over Chathams on Mon 13 Feb and move off to the east --- so that there may be a squash zone between it and the remains of JASMINE. The lobe left behind in the mid Tasman Sea may finally reach North Island on Sat 18 Feb.

That low in the mid Tasman Sea today 12 Feb is disruptive. It has with it the moisture that has been flooding parts of the Australian east coast over the past week. However these clouds are now coming up against a block--- this will slow their motion and as they will drift away from the support of their rising motion the result is likely to be a rather chaotic mixture of patchy rain over NZ on Tue-wed-Thu-Fri 14-15-16-17 Feb. As the low weakens winds around it should slacken, and become no good for sailing but good for motoring for anyone planning a trans-Tasman trip.

Next trough is currently near mid-Aussie bight and should cross Tasmania on Thursday 16 Feb and South Island on Sat 18Feb (preceded by a strong NW flow over southern NZ on Fri 17). It then may stall over NZ into the following week.
Note that I shall be retiring from MetService on Fri 17 Feb (60th birthday) and will be AWAY FROM email Sat/Sun/Mon—should be back on deck with another weathergram by Tue 21 Feb. Also I intend to continue with these weathergrams + with being available to provide weather information to cruising sailors into my retirement--- this is what I call my 'cruise mode'.
The terms used are more fully explained in the METSERVICE Yacht Pack.
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