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

05 April 2015

Bob Blog

WEATHERGRAM
YOTREPS
Issued 5 April 2015
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 Atmosphere:
The Southern Oscillation Index SOI is based on the standardized difference
in the barometer readings between Tahiti and Darwin (30 day running mean)
and sums up the weather pattern over the South Pacific as one number. It. It
switched briefly blue and positive at the start of March but has now gone
very negative again, as Tahiti drops below normal atmospheric pressure and
Darwin returns to normal pressure after recent weather. If it stays this
negative for 3 more weeks then we can call this an El Nino event then again
it may just relax again as it did last November.
SOI is shown at
http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekl
y

TROPICAL TOPICS
We are now in a period of suppressed convection over the South Pacific and
this should last throughout the coming week. The next period of enhanced
convection is forecast to reach northern Australia around mid- April and
then move into the Coral Sea around 20 April.
There is a build-up of convection in the south Indian Ocean and some
tropical lows are forming in that basin.
In the Northwest Pacific TC MAYSAK is travelling westwards across the
northern Philippines, and expected to weaken in the China Sea. Another
cyclone has formed near Chuuk, TC HAISHEN , and it is expected to weaken and
go north.

The rain map for the last two weeks show a buildup in the activity in the
South Indian Ocean and a weakening in the activity in the South pacific.
Weekly rain signatures for past two weeks, may be seen at
http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES
Panama to Galapagos
There is a NE flow around Panama until about local Tuesday and then this
fades. Later in the week the head component of a S/SW wind is expected to
form along the route to Galapagos. So go by local Tuesday if you can.
Good west going current from 2N 85W to Galapagos.

Galapagos to Marquesas:
This week a convergence zone is likely to form along about 5S from 100W to
140W, avoid this by heading for 6S between 95and 100W. Trade winds south of
5S have been moderate to strong for the past week, but if the El Nino
continues to kick in then winds may ease a lot in the next week or so. There
is a good west going current along 5S from 111 to 125W and along 6S from
103W to110W.

SPCZ=South Pacific Convergence zone.
SPCZ is scattered and weak. However a Low is likely to form around Southern
Cooks/Australs from Wednesday, and increasing convection is likely over the
Coral Sea from around 12 April weakening away and mainly over Samoa to
Southern cooks at the beginning of the week. Another new branch may form
over central Coral Sea to Vanuatu by end of week.

STR= Sub-tropical Ridge
The STR extends from Australian Bight to north of NZ and then along 40 to
35S across the pacific.
Next HIGH to cross Tasmania into the Tasman Sea is expected to do so on Fri
10 April, and may take until Fri 17 April before it reaches NZ.

Over NZ
A period of lows. First one is already deepening in Tasman Sea and should
deepen a lot as it passes by southern NZ on Monday. Second is expected to
deepen off Sydney on Tuesday and weaken over central NZ on Thursday/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
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