BOBGRAM issued 24/25 Nov 2013

WEATHERGRAM
YOTREPS
Issued 24 November 2013
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.

Thanks to the yacht people at Opua who came along on Friday and allowed me to share with them my ideas, and for the feedback they gave me regarding my weather forecasting. Thanks also to those in Gulf Harbour who fed and watered me this Sunday evening. All appreciated.

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is the NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

TROPICAL TOPICS
The first cyclone for the southern hemisphere's new cyclone season is TC Alessia and is moving east inland near Darwin over next few days.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is in its northern most position at present and rather weak and disjointed, but it is expected to activate this week and drift slowly south onto Samoa by early December.

Sub-tropical Ridge STR
The STR is now oscillating between its southern latitude band and its northern latitude band. That High which is expected to be over Aussie Bight by Wednesday should move NE into the Tasman Sea by Sunday/Monday, bringing some settled weather to the Tasman Sea area after rather unsettled weather there this week.

Tasman Sea/NZ.
Front in the Tasman Sea is expected to cross the North Island on Wednesday bringing some welcome rain after a dry spell, and this is expected to be followed by a Low. Another weaker trough is expected to cross the North Island on Sunday 1 December, followed by settled weather of a High.

Briefings
Between tropics and NZ
Slack winds for starters this week—then a useful northerly flow from Monday to Wednesday, then a warm front on Wednesday/Thursday, then slack winds again—So weather pattern is not the best for getting from tropics to NZ this week, but if you don't mind doing some motoring and going through a warm front at some stage, then the voyage can be done.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
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