Bob Blog 26 Feb 2017

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.

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The season so far, as shown 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-start/

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.

JANUARY

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FEBRUARY

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Average isobars for 30 days and their anomaly covering last two months from  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 .

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Last 30 days of rainfall, and its anomaly, as seen at TRMM 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, 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.

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Rain for the past fortnight from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES

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Weather Zones (see text) as expected mid-week on Wednesday (GFS model) showing wind, isobars, current, swell black arrows / Sig wave height purple lines, SPCZ and STR.

SPCZ=South Pacific Convergence zone.

SPCZ is weakening and should remain weak over next fortnight.

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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.

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