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

28 December 2014

Bob Blog

WEATHERGRAM
YOTREPS
Issued 28 December 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

The Ocean: extra heat has been stored in the Pacific Ocean for a while now
and all the Oceanic indices have crossed the threshold into El Nino
territory.

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean)
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. It has been negative since July and dived below -10
(Australian units) for much of September, and again for a week in November,
then relaxed in early December, but last week started another negative dive.
The atmospheric El Nino is stuttering.
In an El Nino event the latitudes of the normal weather zones are drawn
closer to the equator, causing the South Pacific Convergence zone to shift
further north and east of its normal position.

TROPICAL TOPICS
The tropical low that formed last Wednesday between Samoa and
Rarotonga/Tahiti has travelled SE and faded.
Rain intensified in the South Pacific Convergence Zone last week. It also
reached deluging levels over Sri Lanka (with the arrival of a tropical Low)
and over Malaysia (as a monsoon---the most intense in decades).
Also at present there is a tropical depression situated east of Philippines,
travelling west, also TC KATE to SW of Cocos Island in the South Indian
Ocean.
And in the South Pacific another tropical low has formed today, just east of
Samoa. The latest thinking is that this South Pacific system may soon move
SSE with slight intensification getting close to Niue/Rarotonga by local
Monday.

Tropical Disturbance Summary For area Equator to 25S, 160E to 120W ISSUED
FROM RSMC NADI Dec 28/0126 UTC 2014 UTC.
TROPICAL DEPRESSION TD05F CENTER [1000HPA] ANALYSED NEAR 13.0S 169.0W AT
280000UTC. TD05F SLOW MOVING. POSITION POOR BASED ON MTSAT IR/VIS IMAGERY
AND PERIPHERAL OBSERVATIONS. SST AROUND 30 DEGREES CELSIUS.
CONVECTION REMAINS PERSISTENT IN THE PAST 06 HOURS. ORGANISATION REMAINS
POOR. THE SYSTEM LIES UNDER AN UPPER DIFFULENT REGION IN A MODERATE SHEARED
ENVIRONMENT. OUTFLOW GOOD TO THE SOUTHEAST. CYCLONIC CIRCULATION EXTENDS UP
TO 500HPA.
GLOBAL MODELS HAVE PICKED THE SYSTEM AND MOVE IT SOUTHEASTWARDS WITH SLIGHT
INTENSIFICATION.
POTENTIAL FOR TD05F TO DEVELOP INTO A TROPICAL CYCLONE IN THE NEXT 24 TO 48
HOURS IS LOW.
NO OTHER SIGNIFICANT TROPICAL DISTURBANCE ANALYSED OR FORECAST IN THE AREA.
Fiji Met Service tropical disturbance discussion above is as at
http://www.met.gov.fj/aifs_prods/20036.txt
If you are in this area then please remain vigilant and keep up to date with
these latest TC bulletins.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is strong east of the dateline with strong NW winds on its northern
side, strong SE winds on its southern side and gale force squalls in-
between. A new branch is expected to form over Coral Sea from mid-week.

STR= Sub-tropical Ridge
A new High cell is crossing the South Island tonight and is expected to
merge with the quasi-stationary high near 40S 170W by mid-week, making a
larger High centered near 45S. This High should then travel east for the
remainder of the week along 45S.
The next High is expected to enter the central Tasman Sea on Wed/Thu and
fade on Friday. Another High is expected to cross Tasmania on Thursday and
then move east crossing central NZ over Sat 3/Sun 4 Jan. Good by then for
holiday weekenders.

Over NZ
Trough between Highs is expected to reach central Tasman by Tuesday and
cross NZ on Wednesday in time for local New Year s Eve. This should be
followed by a period of disturbed SW/S winds and fronts on Thursday and
Friday.

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