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

16 February 2014

BOBGRAM issued 16 Feb 2014

WEATHERGRAM
YOTREPS
Issued 16 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.

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) has relaxed from its recent high. Its 30-day
running mean was over plus 1 for late Jan/early Feb and then dropped. it
was 0.58 on 15 February.

German Scientists Josef Ludescher et al have published a paper in the past
week which claims that El Nino episodes can now be detected as much as a
year ahead and that there is a 75% chance of one starting late in 2014. The
abstract of their paper is at www.pnas.org/content/111/6/2064.
abstract

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 widest and 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. When SST in the target zone (equatorial Pacific between
dateline and Galapagos) are notably cooler than normal, this is called a La
Nina episode.
The SST in the target zone as measured via satellite is in the blue (cooler
than normal) at present, but not by much. The cool blue hue covers much of
the SE Pacific with a broad brush at present as seen in the latest NOAA
satellite data. There is also blue stuff in the Tasman Sea and around NZ -
this indicates an early start to autumnal conditions here, and also may
demotivate any tropical systems that may move onto NZ during the next few
weeks,

TROPICAL TOPICS
Weekly rain accumulated images show that the most intense rain last week was
about and south of southern French Polynesia- even more intense than the
reported trouble spots :eastern USA or southern UK.
There are No tropical storms at present The risk of tropical cyclone
formation in the South Pacific is expected to remain low this coming week.
The Monsoonal trough in Australia is starting to vent its energy across New
South Wales and is expected to breed some lows that may deepen as they cross
the South Tasman Sea/ South Island area on 17-18 February and again on 20-22
February.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The South Pacific Convergence zone is expected to become active over
Solomons and Vanuatu and Fiji, and drift south of Fiji by Friday, allowing a
sub-tropical low to form between Fiji and NZ on Sat 22 February. This low is
expected to the drift SW towards Norfolk Island by wed 26 February.
A second branch of the SPCZ is likely to harass islands from Samoa to
central French Polynesia.
And southern Islands of French Polynesia (Tuamotu/Gambier) are likely to
have a cold front (associated with a low in the southern ocean) move across
them on Wed to Friday 19/21 UTC.

Sub-tropical Ridge STR
The 'Cicada' High that was introduced to NZ in last week's Weathergram is
likely to move to east of NZ on Monday/Tuesday and then hover near 170W
until Friday 21 Feb and then roll off to the east-so this week it is
expected to maintain a ridge 'back' onto part of NZ , helping the cicada
chirp by day.
The next high is expected to travel quickly across the Australian Bight
during the week, cross Tasmanian on Sat 22 Feb and then the South Tasman Sea
on Sunday and central NZ on Monday 24 Feb

New Zealand area
Intense front is expected to cross South Island on Mon/Tue 17/18Feb Weak
ridge from the 'Cicada' High should return on Wed/Thu 19/20 Feb Then a more
intense front and associated low from the Tasman Sea should cross southern
(and affect central) NZ on Fri/Sat 21/22 Feb followed by a cool and windy
S/SE flow (over all NZ) on Sun 23 Feb.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
right to subscribe. Weathergram text only (and translator) is at
weathergram.blogspot.co.nz My website is at metbob.com - To unsubscribe from
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