BobBlog

WEATHERGRAM
YOTREPS
Issued 19-20 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
relaxed to zero in early March and then went negative, to be -10 units for a
few weeks in late March/early April, but is now relaxing again.
SOI are shown at
http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekl
y

The Ocean
The amount of heat that is being stored in the sea in the Eastern Equatorial
pacific has been above normal since late 2014, as measured by the
NINO3.4index, and is currently increasing.
NINO3.4 as shown at
http://www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi,
confirming a trend towards El Nino.

El Nino s impact: During an El Nino episode, weather patterns tend to be
drawn closer to the equator. The subtropical ridge in the southern
hemisphere tends to be north of its normal position and this weakens the
trade winds. The South Pacific Convergence zone tends to be tugged north and
east of its normal position.

TROPICAL TOPICS
The tropics are quiet at present.
The rain map for the last two weeks show the paths of two cyclone sin the
Indian Ocean, and a weakening of activity in the past two weeks in the South
Pacific. Notice how mirror tropical Convergence zone near 4 to 5S from
near 100W to 130W has weakened in the past week. Weekly rain signatures for
past two weeks, are seen at
http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES

Panama to Galapagos
There are some OK NE wind for departure on local Monday this week and on
local fri/sat/sun 24/25/26 next weekend but otherwise the outlook is no
good: either light wind or contrary wind.
There is a good west going current forecast near 1N and to the Galapagos.

Galapagos to Marquesas:
Good winds for departing mainly local Tues/wed/Thu, but a departure on local
Monday will work ok.
This week a convergence zone is still likely near 4 S from 100W to 130W,
avoid this by heading for 5S between 95and 100W. There is a good west going
current along 5S from 100W to 120W.
By local Tuesday 28 April; Winds around Galapagos, as seen at www.
windyty.com, showing bands of counter-wind: west and SW winds near the
equator kicking in:
This is an El Nino sign. Note how the trade winds are staying undecided
to south of 5S.

SPCZ=South Pacific Convergence zone.
SPCZ is reasonable north of NZ this week, A High cell is expected to form
East of the South Island by Tuesday 21 April and then travel east along
45S, so that it bananas a low on its northern side, east of NZ; no good
for cruising.

STR= Sub-tropical Ridge
SPCZ is reasonable north of NZ this week, Next significant HIGH is expected
to ridge into central Tasman Sea AROUND
2-4 May, not before.

Departing from Northern NZ for the tropics.
Good to go on Monday and OK to go on Tuesday but a departure on Wednesday is
likely to encounter fresh head winds for a while from a passing trough on
Sun 26 April.

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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