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

21 February 2016

Bob Blog



Issued 21 February 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.

Tropical cyclone WINSTON

During Saturday (local) the eye of Cat 5 TC WINSTON made a direct hit over Vanua Balavu and Koro,

and last night it skirted across the north coast of Viti Levu.

Death toll is at present 7, and contact is still to be restored with several Islands.

It has today been travelling west, still Cat 5 and is expected to turn south on Monday local.

Computer models come up with different possibilities for WINSTON later this week

– most likely it will weaken as it encounters cooler seas and turn west around the south of New Caledonia.

On my illustrated site i show the lots of barometer and winds from Nadi last night from

from (only aviators know about Density Altitude).

These show Gusts to 70 knots = 130 kph

Fiji Met service Radar shows that the southern half of WINSTON was weakened as the system encounter the mountains of Viti Levu:

See for the animation

And WINSTON delivered over 800mm of rain in a day to several parts of Fiji.

Estimated gust intensities in TC WINSTON from JTWC of 160 knots makes WINSTON the most intense Southern hemi TC.

So says the media, but this will need to wait until the post-storm data verification analysis before becoming official

– RSMC already is coming in with lower numbers (mind you, WINSTON seems to be intensifying again tonight).


TC URIAH in the Indian Ocean is weakening at 26S as it leaves the tropics.

At present there are no other cyclone around, but the South Pacific Convergence Zone SPCZ has a long stretch of near equatorial westerly/northwesterly winds along its northern side. There are some interesting tropical depressions along the South Pacific Convergence Zone, one in the Coral Sea and another near Tahiti. Also a third tropical depression may form near American Samoa during their local Monday—they are near the middle of the confluence between the near equatorial westerly winds to the north and the SE trade winds to the south.

Rainfall in the tropics (seen at

over the past week shows the weakening over convection to NW of Australia and the activating of convective rain

along the South Pacific Convergence zone.

Panama to Galapagos:

As for departing this week--- Not as good as last week. Some convective showers are likely near 5N on local Wednesday and Thursday

followed by a burst of strong NE winds from Panama to Isla del Malpelo from local Friday to local Sunday.

Either get south of 5N by end of Wednesday r wait for a better pattern.



SPCZ=South Pacific Convergence zone.

The SPCZ is now very active, and indeed may be reaching its seasonal maximum in intensity this week.

It is capable of producing another one, may be two tropical cyclones before it weakens.

There may be one of the e cyclones forming near American Samoa by mid-week. Hard to tell for sure,

so plan for the worst and hope for the best.


STR= Sub-tropical Ridge

HIGH travelling east across NZ this week is very strong and supported well aloft.

It should easily be able to deflect WINSTON to the west. There is a chance that WINSTON’s moisture

may be captured and entrained into the next trough that follows this HIGH.


For NZ and Tasman Sea

Trough is expected to visit Tasmania and south Tasman Sea on Wednesday local and cross South Island

and central Tasman by Friday and maybe stall over North Island on Sat/Sun 27/28 Feb.

Its rain depends on how much it entrains from the tropics.



See my yotpak at for terms used.

See my website for information on tailor-made voyage forecasts

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