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

01 May 2016

BobBlog 1 May 2016

WEATHERGRAM

YOTREPS

Issued 1 May 2016

Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: WIAMOPAC= Weather is a mix of pattern and chaos; these ideas are from the patterned world.

Monthly averaged winds:

 

C. M. Risen and D.B Chelton produced the SCOW (Scatterometer Climatology of Ocean winds) at numbat.coas.oregonstate.edu/scow/index.html. Christian Feldbauer of SY PITUFA (currently in Tahiti) has recently made this data available for easier web page viewing at www.pitufa.at/oceanwinds/. He has also (in 2010) made the data available as a kmz file for Goggle Earth viewing

at www.pitufa.at/wp-content/uploads/2010/12/prevailing_ocean_winds.kmz

Thanks Christian

We can compare the May data with what happened with last month’s wind from www.esrl.noaa.gov/psd/map/images/fnl/sfcwnd_30.fnl.gif

And the anomalies from www.esrl.noaa.gov/psd/map/images/fnl/sfcwnd_30a.fnl.html

These maps show that last month the main difference from normal in the Southern hemisphere has been a strange shift to the south and buildup of the “Andes” HIGH located west of South America. There was also a burst of near equatorial westerly winds between Tuvalu and Northern Cooks, possibly an artifact left over by AMOS.

 

The Tropics

Nothing much happening at present.

Rain maps for the past fortnight (from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif) show that the extra convergence zone that has been located between Galapagos and Marquesas is continuing to weaken. It also shows a weakening of intensity in the South Pacific convergence zone.

 

Panama to Galapagos:

It seems there are still a few yachts interested in this route, so I’ll mention prospects for a few more weeks.

This week the best looking date to go is local Tuesday 3 May/Wednesday 4 May (lighter winds for starters).

 

Travelling to Marquesas:

Now that the convergence zone that was in-between Galapagos and Marquesas is weakening away, the optimal route may be north of the direct route, making use of the strong near equatorial currents. Winds near Isla Isabela are expected to be Ok for departure on local Sunday and Monday and again on local Wednesday.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is expected to be weak and recovering this week, mostly around Tuvalu and Tokelau, but also a branch along 15S from 140 to 165W.

 

STR= Sub-tropical Ridge

The HIGH that crossed the North Island this weekend is expected to linger to NE of NZ and became a BIG FAT HIGH (BFH) until it fades on Friday. This is likely to also form a STRONG squash zone on the north side of the BFH and near southern Tonga especially on Tuesday and Wednesday Tongan dates. Avoid.

Another HIGH is expected to cross South Island on Friday and then build to east of South Island from Saturday 7 May.

 

Between NZ and the tropics

It is not an ideal weather pattern for travelling north from NZ this week, but a reasonable voyage to Tonga can be achieved by going east at first in the northerly flow on the rear end of the BFH. Since the BFH is expected to fade by Friday, that’s when a turn to the north can be taken that will go to Tonga in easterly winds.

At present the outlook for next week is for passing troughs, so not very promising.

>>>>>> 

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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2 comments:

St. Farnando said...

Hi there
A scatterometer or diffusionmeter is a scientific instrument to measure the return of a beam of light or radar waves scattered by diffusion in a medium such as air.Take a look at-scatterometry

Thanks

Luis Velez said...
This comment has been removed by a blog administrator.

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