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

23 December 2018

Bob Blog 23 Dec

WEATHERGRAM

YOTREPS

Compiled Sun 23 Dec 2018

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.

 

Today’ weathergram includes a link to a recent video from Mainsail that looks at marine meteorologists around the world—from dingy sailing to America’s Cup/Volvo/Vendee Glob races to forecasting for solo around the world sailors.  This video requires a good Internet connection, but should give you some “holiday” viewing that may share some of what motivates us meteorologists.

See

edition.cnn.com/2018/10/15/sport/mainsail-october-weather-americas-cup-spt-intl/index.html

 

At Christmas time we start thinking of the prospects for the Sydney Hobart Race starting on Boxing Day:

 

See sailing.org/news/88257.php

In an early forecast prediction, the Bureau of Meteorology's Simon Louis told a selection of navigators at a Rolex Sydney Hobart Yacht Race press conference at the Cruising Yacht Club of Australia today to expect a little of everything in the early stages of the 628 nautical mile race.

Louis said, "The long-range weather models show relatively light winds as the yachts leave Sydney Harbour, but with a 15-20 knot (and gusts to 35 knots) north to north-easterly winds which should continue during Boxing Day night and into the next day, with the breeze expected to go around to the west later." This scenario will leave some dead spots in between.  The model is also showing a weak trough over the far NSW coast throughout this period, with lighter and more variable winds off the far south coast and into Bass Strait.

 

 

THE TROPICS

Latest cyclone activity and TCFP tropical Cyclone Formation Potential as seen at www.ssd.noaa.gov/PS/TROP/TCFP/index.html or tropic.ssec.wisc.edu

 

CILIDA is travelling off to the southeast in the South Indian Ocean.  NE of this is a tropical depression named  KENUNGA  (from last week) near 18S 77E travelling southwest.

There is a near 20% probability of development in the next few days around Micronesia and up to 6% probability of a tropical cyclone forming around the northern part of Australia or in the Coral Sea.   This probability increases with time into the New Year, so if interested in sailing in that area, “you’d better watch out”.

This footprint of increased probability is consistent with an MJO oscillation of increased convection travelling eastwards from the Indian Ocean to the Pacific Ocean over the next few weeks.  When an MJO does this in December we usually have a period of near-equatorial westerly wind appear—and sure enough one of these is forming now around Papua New Guinea and likely to extend to almost 180 longitude  by the end of this week (as may be seen at windy.com).

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active between Papua New Guinea/central and northern Vanuatu/ Samoa at first this week and is expected to drift south so that it may reach New Caledonia /Fiji/Tonga by the end of the week.  A tropical Low is likely to develop in the Coral Sea by early next week.

 

Subtropical ridge (STR)

 HIGH forming over Chatham Islands on Monday is expected to travel eastwards along 40S this week.

HIGH forming in western Tasman Sea on Monday is expected to travel eastwards and widen so that it spreads onto NZ on Sat/Sun 29/30 Dec, after affecting the Sydney-Hobart race. 

There is likely to be a squash zone of enhanced SE winds on the north side of these travelling Highs.

 

Troughs around Tasman/New Zealand

LOW is deepening to NW of NZ on Monday and expected to travel southeastwards across North Island on Tuesday/ Christmas Day, and then clear off to the southeast across Chatham islands on Wednesday/Boxing day, followed by a cool southerly flow for a few days over NZ, – with peak southerly swells along East Coast on Thursday/Friday.

  

Between Tropics and Australia.

With a high in the Tasman Sea and low pressures in the Coral Sea, expect strong easterly winds between New Caledonia and Queensland.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

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