Bob Blog

WEATHERGRAM
YOTREPS
Issued 22 March 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: PAM and BAVI (and maybe NATHAN as well) were
triggered by a period of strong equatorial westerly winds (strong enough to
affect Kiribati and Tuvalu early in March).
This reversal of the trade winds is likely to result in the warmer than
normal sea surface that has recently been in the western equatorial Pacific
to shift east during the next few months, and this may show as a tendency to
El Nino. The atmosphere seems to be going hat way already, as seen by the
behaviour of the SOI diving negative in past two weeks, but that may just be
because of lower-than-normal pressures recently over French Polynesia.
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 switched briefly blue and positive at the start of March but has now gone
negative again.

TROPICAL TOPICS
NATHAN has weakened a lot since last week and travelled west. It is still
travelling west, towards Darwin, and should fade away by
Wednesday.
We jumped the letter Q after PAM and the next cyclone is a tropical low that
has formed over the Lau group of Fiji. Named REUBEN it is category 1 and
expected to wobble SE then S and weaken over the over sea: Latest on REUBEN
can be seen at http://www.met.gov.fj/aifs_prods/65648.html
Another cyclone is expected to form over the Northern Cooks by Tuesday UTC
and deepen to a very intensive system by Fri/Sat 27/28UTC near Niue
(Thursday/Friday local). Brace for possible major damage.

The rain map for the last two weeks show a shift eastwards of the strongest
convective activity in the South Pacific has shifted eastwards to the
Northern Cooks.

WEATHER ZONES
Panama to Galapagos
OK N/NE winds for starting this week from Panama. Head for west end of Isla
Mapelo and then go direct. The ITCZ is occasionally bringing tropical
downpours on this route between 5 and 4N. There is a strong west-going
current forecast near 1N from 84 to 87W.

SPCZ=South Pacific Convergence zone.
REUBEN is already out of the SPCZ and taking a piece of its energy out of
the tropics.
SPCZ is very intense this week over Samoa to Northern Cooks and this is
expected to help a cyclone form over Northern cooks by Tuesday UTC (Monday
local).

STR= Sub-tropical Ridge
The main STR is returning to its normal latitude at 40S around NZ.
A HIGH is expected to build east of NZ on Monday and Tuesday and then move
off to the east on Wednesday and Thursday allowing the remains of REUBEN to
travel south along 170W behind it.
The next high is then expected to travel in a thin line across the south
Tasman Sea on Saturday (while a Low lingers in the Tasman Sea) and then
blossom east of the South Island on Sunday and move off to the east on
Monday 30 March.

Over NZ
The low currently spinning in the Tasman has no traction and is likely to
fade away there by Wednesday, but may bring bothersome showers to the
cricket (semi-final) at Eden Park on Tuesday.
Another low is expected to cross the Tasman Sea on Tuesday and Wednesday and
fade over North Island on Thursday/Friday.
Another low is expected to cross the central Tasman Sea on
Thursday/Friday/Saturday/Sunday and then NZ on Monday and Tuesday
30/31 March.

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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