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

16 September 2018

Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 16 Sep 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.

 

Equinox is next Sunday:

Next Sunday, 23 Oct at 01:54 UTC marks the vernal equinox. At this point in time the overhead sun is directly over the equator, shifting from the northern hemisphere to the southern hemisphere.

 

If you check sunrise /sunset times for your place for Sun 23 Sep, you will find that these compute to something like 12hr 7mins of sunlight. This is because sunrise and sunset are defined with respect to the top limb of the sun, rather than the centre of the sun, and that adds a few minutes of sunlight to the day. You’ll find (if you look) that the day that has closest to exactly 12 hours of daylight, called the equilux, is around three days earlier than the September equinox.

 

Somehow, I was thinking that New Zealand switched to Daylight time on the fourth Sunday of September--- but no, the change occurs on the last Sunday of September, and so that’s 30 September

 

The change to daylight saving occurs on different dates for the nations around the South Pacific so I think it’s a good idea for you to have a summary for reference

 

Date Place Daylight saving time zone

30 Sep New Zealand UTC+13 (NZDT)

30 Sep Chatham Islands UTC+13h45mins (CHADT)

7 Oct Lord Howe Is. UTC+11 (AEDT)

7 Oct New South Wales, Tasmania UTC+11 (AEDT)

4 Nov Fiji UTC+13 (Fiji Summer Time FJST)

No changes in Tonga or Norfolk Island or Queensland or New Caledonia.

 

As yachts start their end-of-spring migration, with the approaching South Pacific Cyclone Season, it is also useful to have a summary of the various national holidays, as these limit available departure dates.

French Polynesia 1 Nov All Saints Day, 11 Nov Armistice day (100th year).

Cook Islands: 26 Oct Gospel day

Niue: Oct 19 to 22 Constitution day celebrations, Oct 22 is also Gospel day.

Tonga Sep 17 HRH Crown Prince Birthday, Nov 5 Constitution Day

Fiji Oct 10 Fiji Day, Nov 7 Diwali, Nov 20 Muhammad Birthday

New Caledonia Sep 24 National Day, 1 Nov All Saints Day, 11 Nov Armistice Day (100th year).

New Zealand Oct 22 Labour day.

Australia: OCT 1 Labour Day (ACT, NSW &SA), Queen’s Birthday (QLD)

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TROPICS

MANGKHUT travelled over the northern parts of the Philippines, with a death toll of at least 24 so far. It is now skirting around Hong Kong. FLORENCE weakened as it made landfall over Northern Carolina and has a death toll of 13 so far.

It is purely a coincidence that the Atlantic systems all have female names at present: The males: Gordon and Isaac have faded away

Also the Southern Hemisphere cyclone season is showing signs of a possible early start with the formation of Tropical depression ONE in the South Indian Ocean.

Map of current storms is seen at tropic.ssec.wisc.edu/

Looks like HELENE may end up over the UK this week.

Looking at the weekly rain maps we can see the tracks of last weeks’ cyclones.

There has been an intense area of rain last week over New Britain to northeast of Papua New Guinea.

See trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay in the region from PNG to just south of the Solomons Islands to north of Fiji this week.

Trough over Vanuatu on Monday UTC travelling to south of Fiji on Tuesday UTC and fading over south-of-Tonga on Wednesday UTC.

Convergence zone over Tahiti on Tues UTC and Tuamotu Islands to Gambier Islands on Wednesday UTC. Then a Low may form south of Tahiti by end of the week travelling off to the SE and deepening, stealing the wind for Tahiti

 

Subtropical ridge (STR)

HIGH over 1030hPa to eats of NZ travelling east along 40S. Squash zone of enhanced winds on its northern side between 20 and 25S reaching peak on Tuesday UTC.

Next HIGH should move from Australian mainland into Tasman Sea on Mon/Tuesday UTC, and then fade over central NZ.

 

Around Tasman Sea, NZ.

Low1 crossing the South Island on Monday UTC Low2 is expected to be crossing the area between Fiji and NZ on Monday/Tuesday 17/18 Sep, followed by Low3 on Fri/sat 21/22 Sep. Southerly winds follow these lows.

For those sailing towards New Zealand from Fiji/Tonga/Noumea, there may be a narrow gap between these lows, so that the best-looking voyage this week maybe with a TUESDAY departure, but this does involve zig-zagging around some southerly headwinds.

Traffic going from New Caledonia to Australia have useful south to southeast winds for starters but may encounter a front and southerly winds near Australia from Thursday UTC.

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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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