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

14 May 2017

Bob Blog 14 May

WEATHERGRAM
YOTREPS
Compiled Sun 14 May 2017

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.

Tropical Cyclones DONNA, ELLA and ADRIAN

Cyclone DONNA was tripped over by Mare island in the Loyalty Group and faded quickly with its clouds merging into a trough that crossed New Zealand on Friday. Looking at its track it seems that DONNA had problems when its forward edge started encountering the high ground of New Caledonia. This can still be seen at www.met.gov.fj/aifs_prods/65648.html

Cyclone ELLA is still travelling slowly west, travelling near Rotuma tonight, and expected to weaken on Monday but may still have squalls when it gets near the northern Islands of Vanuatu on Wednesday. This can be seen at www.met.gov.fj/aifs_prods/65663.html

Cyclone ADRAIN had a brief life starting Wed 10 May (UTC) when it formed in the NE Pacific. Their cyclone season usually "opens" on 15 May, and ADRIAN now holds the record as "earliest cyclone" for the NE Pacific. It dissipated on 11 May. See watchers.news/2017/05/10/tropical-storm-adrian-forms-in-ne-pacific-as-the-earliest-on-record/

The rain from cyclone ELLA in the past week is the highlight of this week's rain map, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, especially when compared with last week (which is showing DONNA's rain). Also note that the extra convergence zone that was between Marquesas and Galapagos a fewe weeks ago has now faded away.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
TC ELLA is expected to weaken on Monday but may bring some squalls to norther Vanuatu are aby Wednesday. Apart from that, the SPCZ this week is expected to linger from Solomons to the area between Vanuatu and Fiji. Another convergence zone is likely to longer along 15S between Samoa and the area west of Southern Cooks.

Subtropical ridge (STR)
High over northern New Zealand on Monday is expected to travel to east of NZ along 35 to 40S. There is likely to be a squash zone of enhanced SE winds on the northern side of this High from Wednesday to Friday UTC between Rarotonga and Tonga.
Next HIGH from the Australian bight is expected to linger over Tasmania from Wednesday 17 to Friday 19 May, then travel NE across the Tasman Sea to reach North island around Monday 22 May, and then across the Tasman Sea next week reaching northern New Zealand by Friday 19 May.

Australia to New Caledonia:
The GO EAST RALLY is rearing to go soon.See www.downunderrally.com/about-go-east

The HIGH in the south Tasman Sea from Wednesday is likely to maintain too much SE trade winds along the route until Sat 20 May. Then there should be a weak passing trough on Sunday, but today's data is showing this is NO LONGER EXPECTED to be followed by a change to SW winds. The next possibility for a reasonable weather pattern for departure is around Thu 25 May, perhaps. Things my change and bring this forward, so keep tuned.

Departing NZ to the north for the tropics:
The current weather of opportunity is quickly closing as the next incoming trough is expected to bring NE winds onto Northland from Tuesday. Low in southern Tasman Sea is expected to deepen from Monday to Wednesday as it travels southeast then east, and then across central NZ on Thursday. AT this stage, a departure on Friday 19 or Sat 20 May is looking good.

New Zealand to the east (Tahiti)
After the Wednesday/Thursday trough we may need to wait a day or so for the southwest winds that follow that trough to ease. Then around Sat 20 May there should be an OK opportunity for departure.

Mexico to Marquesas:
Off NW Mexico, there should be a useful north to NW flow for departure for first half of this week, but then these winds may become lighter and more variable for a few days.
The ITCZ is likely to be between 9N and 3N, and light winds between 8N and 5N.
Perhaps there is better sailing if you aim for a waypoint WEST of the direct path this week near maybe EQ131W.

Panama to Galapagos
Light mostly southerly winds off Panama this week, so it's a motoring start and there are moderate SW winds between Panama and Galapagos especially from 16 to 20 May UTC (Mon to Friday local).
Convective clouds with variable winds and squalls likely from 6N to 3N.

Galapagos to Marquesas
There is still a zone of light winds about the equator near 100 to 105W, so go southwest at first. Then, when in the trades, we can go direct.
Maybe a convergence zone with squalls near 5S 100W, avoid.

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