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

05 March 2017

Bob Blog 5 March 2017

WEATHERGRAM
YOTREPS
Compiled Sun 05 march 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.

in 1971 Roland Madden and Paul Julian of NCAR co-authoured a paper showing a quasi-cyclic pulse of convection that travels mostly eastwards around the tropics. This is called the Madden-Julian Oscillation or MJO. It travelled across the South Pacific during early to mid-February triggering 7 tropical depressions and one (brief) Tropical Cyclone.

The South Pacific Convergence Zone has settled somewhat in the past week-no tropical depressions---but it still has the capacity to produce heavy rain. Rakiraki in western Fiji was flooded by downpours today as seen at www.facebook.com/search/top/?q=ndraki%20weather

We are all interested in when the next MJO may reach the South Pacific.
Its phase is measured at www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/forca.shtml
This Phase diagram shows that the next timing for the MJO into Region 6 (South Pacific) is possibly after 11 March. Of course, we may still have tropical disturbances even when MJO is not in our region.

The February MJO may have also triggered the "Pineapple express" on 15 and 20 Feb, whereby moisture is taken by a jetstream from the tropics to west coast of North America producing flooding rain. There have been plenty of these since last October, as seen at
www.mercurynews.com/2017/02/23/why-is-it-raining-so-much-in-california/
An animation demo of this is at phys.org/news/2017-02-nasa-eyes-pineapple-california.html

The tropics
TC BLANCHE formed today off Darwin and is going SW and may make landfall as a Cat 2, as seen at www.bom.gov.au/products/IDD65011.shtml
And in the Indian Ocean TC ENAWO is about to make landfall on to Madagascar.
See www.tropicaltidbits.com/storminfo/

Rain from last week, as at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, compared with previous week, shows heavy rain over Guam area and from TC ENAWO near Madagascar in the Indian ocean. It also shows a gradual decrease in activity over the South pacific, and yet there are still downpours, as at Rakiraki today. The Intertropical Cyclone convergence zone is weak and broken into branches. And there is a convergence zone along 5S from 100 to 125W -remember that the sun directly overhead 5S this week.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to remain much the same this week. The convective energy that triggered the Rakiraki downpour today should be over Southern Tonga on Monday, and may produce a brief Tropical low. The "5 deg convergence zone" is due to the seasons/our solar orbit and triggered when the overhead sun is at 5 deg S. Of course, the overhead sun will be over the equator later this month for the equinox. I bet ya the "5deg conv zone" remains until early April.

Subtropical ridge (STR)
One high is moving off to east of NZ. The next High is expected to travel across or south of Tasmania on Monday and around southern NZ on Tuesday/Wednesday, building east of South island and travelling NE from Thursday to Saturday.

Tasman Sea troughs.
Tasman sea is expected to be dominated by that Low which is deepening off Sydney tonight. It seems to have a closing upper trough above it (main Jetstream too far south to kick it) and the models are at present uncertain about its future. The frontal zone associated with that low may linger over Northland and that's a good recipe for a good soaking (yes please).
If you wish to cross the Tasman Sea this week then stay well to the north.

Panama to Galapagos
Looks good for departure until 13 March with northerly winds for starters.
After that winds are lighter and may be southerly.
Prepare for light head winds south of 5N, and main convection between 5N and 2N,

Galapagos to Marquesas
To avoid the "5 degree convergence zone" go first to around 10s 100W and then direct.
Expect light winds to 5S, then OK SE 10 knots or more. Anticipate light SE winds west of 130W
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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 or txt 6427 7762212
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