Bob Blog

WEATHERGRAM
YOTREPS
Issued 7 June 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 sums up the weather pattern over the
South Pacific as one number and is based on the standardized difference in
the barometer readings between Tahiti and Darwin (30 day running mean). The
weekly update has been lower than -10 for four week now, so that means we
are now having a full blown El Nino affecting both Atmosphere and Ocean.
SOI is shown at
http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekl
y
In an El Nino the normal weather zone get pulled closer to the Equator, and
we can see this in the pressure anomaly map for the past month. The
subtropical ridge in the Pacific is over New Caledonia/Fiji/Tonga. There
are higher than normal pressures over Darwin and lower than normal over
Tahiti. As seen at
http://www.esrl.noaa.gov/psd/map/images/fnl/slp_30a.fnl.anim.html
This trend allows some Meteorological companies to extrapolate it a month
ahead and produce wind anomaly maps such as seen at
http://www.extendweather.com/seasonalforecast/GLOBAL/E3201505/windspeed-anom
aly

TROPICAL TOPICS
TC BLANCA is not following ANDRES (of last week) into the Pacific, instead
it is expected to make landfall over Baja California on our Monday (local
Sunday).
In the Arabian Sea, west of India, there is a tropical depression. However
there is no sign yet of anything forming in the Atlantic, nor in the NW
Pacific during the following week. Strange.
In an El Nino year the Indian monsoon is usually late, slow, and not-so-wet.
And indeed, this year's Indian Monsoon has struggled to keep to its normal
sequence and is now about 5 days BEHIND schedule. Its failure to bring
ocean-moistened air into the heart of India has led to extremely high
temperature to inland India:

Advance of Northern limit of Monsoon may be seen at
www.imd.gov.in/section/nhac/dynamic/Monsoon_frame.htm, extending the
pre-monsoonal heat wave over central India.

The rain map for the last two weeks shows ANDRES and BLANCA off the west
Mexican coast, and also a burst of intensity with the South Pacific
Convergence zo is seen at
http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES

Galapagos to Marquesas:
Best winds for departing are on Monday/Tuesday or Wednesday local.
There is still signs of a good west-going current along around 5 to 6S near
100W but it is now weakening.

SPCZ=South Pacific Convergence zone.
SPCZ has been strong over the Solomons and is expected to be moderate this
week between Solomons and Samoa with a stretch of activity across Northern
Cooks. A trough is expected to cross French Polynesia late in the week and
develop a low near 30S 140W by Thursday UTC (local Wednesday) that should
then move SE.

STR= Sub-tropical Ridge
STR remains north of normal-an El Nino trait. One HIGH is expected to move
east along 30/35S from North Tasman Sea to 150W during this week, with a
squash zone of enhanced trade winds along 25S on its northern side. There
is a large 1030 hPa high over SE Australia: It is expected to move along
35/40S from Australian Bight to Eastern Australia from Wednesday to Friday
and then to eastern Tasman Sea this weekend 13/14 June and hover over
northern NZ early next week.

Tasman Sea /NZ area:
Trough over southern Tasman Sea and southern NZ by Tuesday should cross
central NZ on Wednesday and North Island on Thursday.

Departing from Australia to the tropics this week:
Avoid the squash zone of strong SE winds in the Coral Sea and northern
Tasman Sea from Monday to Saturday- These are on the north side of the large
1030 HIGH over SE Australia.

Departing from Northern NZ going north.
OK to depart on Monday if you are quick enough, otherwise there are nosy
head winds ahead of that incoming trough on Wednesday and strong winds on
Thursday. May be Ok to depart for the north again on Friday or Saturday.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
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