Translator

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

26 February 2017

Bob Blog 26 Feb 2017: 8 Depressions in 4 weeks

WEATHERGRAM
YOTREPS
Compiled Sun 26 February 2017

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.

FEBRUARY
During the middle of Feb 2017, we had an MJO episode cross the South Pacific
triggering EIGHT tropical depressions, of which only one reached (BART) Topical
cyclone - and then only for a day as it left the tropics. The season so far, is
seen at en.wikipedia.org/wiki/2016%E2%80%9317_South_Pacific_cyclone_season

BART was a late starter for the Cyclone Season. It was identified at around
00UTC on Tue 21 Feb 2017 - that's six hours later than TC OMA named at 1800UTC
on 20 Feb 2001--- however the actual start of the cyclone phase, with a little
hand-waving , can easily cover a plus or minus of six hours , so let's just say
we had a late start to our cyclone season this year. See my previous blog
metbob.wordpress.com/2017/02/22/tc-bart-marks-a-late-20162017-cyclone-season-sta
rt/


The MJO has gone now and its next episode in the South pacific may not be until
mid to late March. This should lessen (but NOT dismiss completely) the chance of
tropical depressions in our region over the next few weeks.

Subtropical ridge dominated the South Atlantic and South Indian Ocean, and moved
south onto central NZ but was weak over central South Pacific.

North Pacific still has that "face" with a nose/forehead and two eyes. And
North America is exceedingly troughy/stormy.

Average isobars for last 30 days and their anomaly covering last two months are
at
www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

February rain has mainly been along the South Pacific Convergence zone (those 8
depressions). Two points to note: the Intertropical convergence zone across
the Pacific is much drier than normal. And the "mirror convergence zone "that
occurs every year in early to mid-March between Galapagos and Marquesas (when
sun is directly overhead 5S), has appeared EARLY this year .
Last 30 days of rainfall, and its anomaly, are at
trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

The tropics
No cyclones or tropical depressions anywhere at this stage.

Now that the MJO has gone and the tropical depressions are moving out of the
tropics, things have settled across the South Pacific. The west/northwest winds
of the monsoon that were around earlier this month have been replaced by SE
trade winds bringing in cooler air from the south. It's now OK to do some
Island hopping for a week or two.

Rain from last week at
trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, compared with
previous week, shows a gradual decrease in activity over the South pacific. And
a gradual return to normal along the Intertropical Cyclone convergence zone.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is weakening and should remain weak over next fortnight.
See the Tropical accumulated rainfall for next week from windyty.com

Subtropical ridge (STR)
HIGH crossing the Tasman sea along 42S is expected to cross central NZ then
Northern NZ from Monday to Friday this week--- a good week to go motoring around
NZ.

Tasman Sea troughs.
Next front is expected to reach southern NZ on Fri 3 March and then travel NE
along east coast on the sat/sun 4/5 March weekend, followed by another HIGH.
A coastal trough off eastern seaboard of Australia is likely to bring rain and
fresh onshore winds, getting strong around Sydney by end of the week.

NEW: Panama to Galapagos
Looks good for departure by 5 March in northerly winds. Then not so good for
the following week or so in light winds or southerly winds. Prepare for light
head winds near Galapagos

NEW: Galapagos to Marquesas
Expect only light winds until the convergence zone near 5S, then squally showers
to around 10S then OK in ESE to E 10 knots to Marquesas.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Follow me on Facebook at www.facebook.com/metbobnz/
See my yotpak at boatbooks.co.nz/weather.html for terms used.
See my website www.metbob.com for information on tailor-made voyage forecasts-
Feedback to bob@metbob.com.
Tell anyone you like that to subscribe they should email me.
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.
To unsubscribe from WordPress: click the "unsubscribe" link on the bottom of the
email. Or, if email wasn't from WordPress then send a reply email saying LEAVE.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

No comments:

Blog Archive