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

17 February 2013

BOBGRAM issued 17 Feb 2012

WEATHERGRAM
YOTREPS
Issued 17 Feb 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.
The Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) is based on the barometer readings from Tahiti and Darwin and sums up the weather pattern over the South Pacific in one number. It dived to almost minus 1 during December, relaxed to near zero during January, and has dived to minus 0.9 so far during February. So things may now be tilting in the favour of weather systems that bring SW winds over the South Island (El Nino). But not this week---

To see the SOI for the past few months , updated weekly, view
http://weather.farmonline.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

The Ocean: Sea surface temperatures across the equatorial Pacific act as a thermostat for the planetary weather engine. When they are different from normal we get a change in clouds around the equator and in the latitude zones of weather across the whole Pacific.
Well, in the past month the SST in this target zone has mostly slightly below normal, indicating a tendency towards La Nina in the Ocean. This dichotomy between atmosphere and ocean indicates that the tropics are having a mixed impact on our seasonal weather.

WEATHER ZONES
There is a Madden Julian Oscillation of enhanced convection moving from the Indian Ocean onto northern Australia this week. This can be seen at
http://cawcr.gov.au/staff/mwheeler/maproom/OLR_modes/h.6.MJO.S.html, where the blue zone (of less OLR) marks a strengthening of convection and an increased chance of tropical cyclone formation.
The latest EC model has a tropical cyclone forming off NW Australia this weekend and possibly making landfall around Mon 25 Feb.
Also all the computer models are showing a tropical depression forming off the Queensland Coast on Mon/Tue 18/19 Feb, then tracking offshore and following the coast southwards and deepening as far as 30S then weakening and making landfall over New South Wales around Friday. Avoid.

The South Pacific Convergence Zone SPCZ has strengthened and broadened a lot in the past week and is mainly draped between 10 and 25S, with clusters of convection over Fiji, from Samoa to Marquesas, and south of Southern Cooks. By the end of this week the SPCZ should be in much the same place and continuing strong, with the possibility of a low lingering south of southern Cooks.


The Sub tropical ridge STR extends from Aussie Bight across the Tasman Sea and NZ and then along about 35S. It is at its southern most position- consistent with the time of year.

The High crossing NZ on Monday is expected to move off to the east on Tuesday.
Another High is expected to cross South of Tasmania on Wednesday and then its eastern side is likely to fade south of NZ on Thursday. Its western side is expected to skirt the South Island SE coast on Friday and blossom east of or over the South Island during Sat/Sun 23/24 Feb.

There is one front between those two highs. It is expected to be over the South Island on Wed 20 Feb and should then peel off to the east, but may help a trough to form off NE of NZ on Thursday and Friday- and that may make for a SE flow for the TELECOM THREE KINGS race being held by Royal Akarana Yacht club.
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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://metbob.wordpress.com
Weathergram text only http://weathergram.blogspot.co.nz
Website http://www.metbob.com
Feedback to bob@metbob.com

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