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

03 April 2016

bob blog 3 april

WEATHERGRAM

YOTREPS

Issued 3 April 2016

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.

 

Congratulations to Donna Lange, who has successfully made it to Panama (29 March local) after her Yacht, Inspired Insanity, suffered two knockdowns and damage mid-February when about a week away from Cape Horn. Donna had to do the leg to Panama without any communications on board. You can read about her adventures at www.sailblogs.com/member/sailtwicearound/ (click on a recent blog and then keep clicking older at top right of blog window to get to the blogs on arrival).

 

That ‘extra convergence zone’ which has been between Galapagos and Marquesas since the equinox is STILL expected to affect travellers along this route for the next week.  Best seen on windyty.com using the rain accumulation of next ten days setting:

This extra convergence zone marks the north end of the SE trade winds, and there are only light winds between it and the Intertropical convergence zone—- these may be from the west, so are worth. Thus the best path at present from Galapagos to Marquesas is to get south of the extra convergence zone.

 

MARCH REVIEW

The averaged isobars of March show a strong subtropical ridge over the oceans in both hemispheres, with anomalously high pressure centres over North sea and Korea in northern hemisphere and dotted along the Southern hemisphere subtropical ridge and over South America.  This can be seen at www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The map shows how New Zealand was often afflicted with “eggbeater NE winds” caught in-between the rotating wind around a large High to the east and a low over the Tasman Sea.

 

TROPICS

AT present there are no cyclones around. But there are two tropical depressions on the South Pacific Convergence zone between Vanuatu and Fiji:

This duet of tropical lows are currently deepening and have a moderate chance of becoming tropical cyclone with gales (at least) near their centres by Wednesday mid-week. TD 14F is also known as 96P to Guam and they have produced an ensemble of possible future tracks . This can be seen at www.tropical tidbits.com

These systems are moving quite quickly so are not expected to affect any particular spot for long, but are likely to being squally weather to Fiji especially on Tuesday and Wednesday local.

 

The rain maps for the past week or two show that the extra convergence zone is starting to weaken from its western side. And Australia had a dry week last week.

Rain for the past fortnight may be seen at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

Panama to Galapagos:

After a period of light winds, the forecast is for good NE winds from local Monday to local Saturday this week. Convection is mainly around 4 to 6N and mostly west of 85W so not much of a problem. No real advantage this week in going via Isla Del Malpelo, so may as well follow the current to 4deg N 83W then go direct. This waypoint may vary, so email me if you’d like a tailored waypoint.

 

Travelling to Marquesas:

Light winds around Galapagos. The west-going current near the equator is becoming random in strength and position—and the winds in-between the ITCZ and the extra convergence zone are light and variable, sometimes westerly, so those factors rule out that route. Going direct means encountering squalls in the extra convergence zone, not a good idea. SO the way to go is to get south of the convergence zone and skirt its southern edge.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is expected to spend this week very active from Solomons to northern Vanuatu to Fiji /Tonga area, with north edge near Samoa. Keep watch for there may be two tropical cyclones by mid-week, travelling SE across southern Fiji/Tonga.

 

STR= Sub-tropical Ridge

New HIGH is expected to travel east across Tasman Sea on Monday/Tuesday, and central NZ on Wednesday then split into two centres, one fading over northern NZ by weekend and t’other travelling east along 45S.

 

For NZ and Tasman Sea

A trough is forecast to travel across the Tasman Sea and deepen as it crosses the South Island on Thursday, then weaken as it crosses the North Island on Friday, followed by decreasing southerly winds.

 

>>>>>> 

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.

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Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

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