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

01 November 2015

BOB Blog 1 Nov 2015

WEATHERGRAM

YOTREPS

Issued 1 November 2015

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 genesis and occurrence: A weekly treasure:

The Meteo France weather Office in Noumea have started a page on their web site which translates the latest phase of the MJO (Madden Julian Oscillation= a quasi-cycle that travels from the Indian Ocean across Northern Australia to western pacific around once every 3 to 6 weeks, encouraging extra convection) into maps showing the probability of occurrence or genesis of tropical cyclones. These can be found at http://www.meteo.nc/cyclone/coin-des-experts (then click on the example graphics to get the latest).

These maps show that the MJO is active in the Indian Ocean at present—and this implies that it may get to the western South Pacific late this month or early December.

I suppose this means that there is no immediate hurry for departing the tropical South Pacific. However If your marine insurance becomes void in the cyclone season (and many Insurance Companies define that as from 1 November for South Pacific) then your financial risk has risen overnight.

 

TROPICAL TOPICS

In tune with the MJO, there is just one active tropical cyclone at present and it’s near the horn of Africa. CHAPALA, heading for Yemen. See http://www.tropicaltidbits.com/storminfo/

 

The Weekly rain maps, as seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif,

show steady convection over western part of Indian Ocean, and a weakening over the whole Pacific Ocean.

 

WEATHER ZONES

 

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to have a reasonably quiet week mainly near Solomons to Tuvalu and Tokelau, with scattered convection over Southern cooks/French Polynesia. There may also be some shower activity for Wallis and Futuna.

 

STR= Sub-tropical Ridge

The axis of the STR is strong along 30S from north of NZ to south of Pitcairn Island. Strong enough to provide a zone of light winds for yachts heading to NZ from the tropics. Nothing much can be done about this except for motoring in light winds. The pattern seems to be in place until at least mid-month.

The HIGH that is in the Australian Bight tonight should cross south of Tasmania on Tuesday and then travel NE across the Tasman Sea and stall over northern NZ from Sat to Tues 10th and then be replaced with another High keeping a ridge over or to north of northern NZ from Wed 11 to Sat 14 Nov.

 

Over NZ/Tasman:

The front moving NE over southern NZ on Monday is expected to receive a developing low from Australia on Tuesday and deepen this over central NZ on Wednesday so that the low hovers to east of the North Island from Wed to Friday (an olde man southerly), and the lingers off to NE of North Island from Sat to Mon 9 Nov (cut off upper low).

There are likely to be SW winds partly on the way between NZ and Tonga from Thursday to Sat 9 Nov.

 

Travelling Tahiti to Marquesas.

Easterly winds and minor convergence zones. May be NE winds locally over Tahiti on local Sunday/Monday.

 

Travelling Tahiti to Tonga:

The SPCZ should stay north over most of this route and is weak over Tahiti.

No squash zones this week. A trough is expected to travel from Tonga to Niue this weekend, Sat/Sun 7/8 Nov UTC, bringing light variable winds, maybe some SW winds and a few showers.

 

The Island Cruising Association is holding the All Points rally to Opua and the Downunder rally from Noumea to Newcastle.

Between Tropics and NZ: for the All Points Rally, ending in Opua:

A weak trough is expected to form over the Minerva area on local Thursday and travel to Tongatapu by Friday night, with variable light winds, and followed by a period of SW/S winds--- This isn't a major problem but does take the edge off the comfort of any departures from Tonga on Thursday and Friday.

Departures from Tonga (and sometimes Fiji) to NZ this week have some S/SW winds to divert around, especially from Thursday to Saturday—and this can be done by going far enough WEST before the southerlies and encountered, but does slow and lengthen the voyage.

Departures from Fiji and New Caledonia have that subtropical ridge axis to cross—a zone of no wind near 28 to 30S.

AT this stage, looking 5 days plus ahead, it seems that there are no dates to avoid for arrival in NZ, but onshore easterly wind are expected over NE NZ on Tuesday 10 November so maybe avoid that day.

 

Between Tropics and Australia

For the Downunder Rally (Noumea to Newcastle) Hmmm. A Low from the heat of the interior of Australia is expected to travel east along 35S across New South Wales and into the Tasman Sea on Thursday bringing a SW change into Newcastle on Friday 6 Nov. This may not be a gale—but the rain (mainly on Wednesday) should be squally.

The associated trough should weaken quickly but linger along 30S.

Departures from Noumea this week before Thursday are likely to just encounter some of that left-over trough near 30S. On Monday 9 Nov there may be STRONG northerly winds and squally rain near 30S – avoid.

>>>>>>

 

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. Tell anyone you like that to subscribe they should email me.

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