BOB's BLOG issued 23 Feb 2014

WEATHERGRAM
YOTREPS
Issued 23 February 2014

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.

In the past few weeks the northern winter has been brutal in eastern US and
over UK. The jet streams have had more latitude coverage than normal, and
have maybe been held in position by a blocking pattern. Also the stronger
than normal upper winds may have been extended higher upwards in the
atmosphere by a westerly phase of the Quasi Biannual Oscillation  a weather
driver in the stratosphere.
The QBO can be seen at the NCEP website.

SOI The Southern Oscillation Index SOI sums up the weather pattern over the
South Pacific as one number. It is based on the standardized difference in
the barometer readings between Tahiti and Darwin.
SOI (30 day running mean) continues on its roller coaster ride for 2014.
It peaked on late January/early February and is now sliding down. On 23
February the 30-day running mean was 0.13.

TROPICAL TOPICS
Weekly accumulated rain maps show a buildup of rain around Papua New Guinea
in the past week, due to enhanced equatorial westerlies.
There are no active tropical storms at present. The risk of tropical cyclone
formation in the South Pacific rises to MODERATE this week, with the most
likely areas being between Vanuatu and Fiji. Most models are picking this
development to likely occur around Wednesday with the disturbance then
moving S and then SE, and the associated trough crossing
Tonga and Niue on Sat/Sun 2/3 March. Avoid.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The South Pacific Convergence zone is expected to remain active between
Papua New Guinea and Tonga/Niue. Another, weaker, zone is expected to hover
between Tokelau and French Polynesia.
There has been a burst of near equatorial westerly winds across the Timor
Sea last week and this is currently travelling from north of the Solomons
towards Tuvalu. It is likely to help aid the formation of a Low near Fiji by
Wednesday.

Sub-tropical Ridge STR
That Cicada High mentioned in last weeks Weathergram managed to bring
warm temperatures to NZ. It has travelled off to the east and that trough
which crossed NZ last weekend is followed by a few days of cooler southerly.
The HIGH now in the Tasman Sea is expected to cross central NZ and move off
to the east by Thursdaynot as long and not as warm as last weeks HIGH.

New Zealand area
A cold front is expected to lick the southern areas on Monday.
Then a combo of fronts is likely to spread a trough and then southerly
change across the whole of NZ during Thursday 27 to Sat 1 March.
Then another slow-moving HIGH is likely for the following week.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
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