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

18 October 2015

Bob Blog 18 0ct 2015

WEATHERGRAM

YOTREPS

Issued 18 October 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.

 

Bureau of Meteorology Australia have now issued their 1015-16 Tropical cyclone season outlook and they are going for a less active season.

See http://www.bom.gov.au/climate/ahead/tc.shtml

This ties in with the NIWA, MetService NZ and Fiji Met Service outlooks given here last week going for a more active season in our part of the South Pacific (east of 160E). Basically the activity is shifted eastwards by the El Nino episode we are having.

Now, since a lot of tropical Cyclone and Depression activity starts along the South Pacific Convergence Zone, it’s expected average position should show where most of this season’s tropical Cyclones are likely to form.

NIWA have published an  image showing this earlier this month as part of their Island Climate Update at

http://www.niwa.co.nz/island-climate-update-181-october-2015

and it shows the expected average position (green line) from now until December for the SPCZ from an ensemble of global climate models. The red line is the climate average for this time of year, showing how far north (and east) is this seasonal shift. In the image, brighter shades of purple show the expected wetter areas—showing that western Solomon Islands to Tonga are NOT expected to have much of a wet season this year.

Since many insurance companies define the South Pacific Cyclone Season as being from 1 November to 30 April (and remove their cover accordingly), a lot of yachts are likely to leave the warmth of Tonga /Fiji/New Caledonia and head for Australia/ New Zealand. (Small note: Minerva reef at 24S is technically OUT of the tropics, so even if your insurance cover may be void from 1 Nov in Tonga, it remains valid in Minerva forever!).

The Island Cruising Association is especially geared up to help those wishing to spend the cyclone season in NZ, and organise an ALL POINTS RALLY for this. It’s free (thanks to the sponsors) and helps yachts with weather info, resources and planning tools to try and make the passage as easy as possible. In Opua participants are offered a week of fun, entertainment and seminars, starting 16 Nov. It’s a bit late now, but if you want to sign up go to http://www.islandcruising.co.nz/?page_id=717

Australians do not want to be outdone and this year have started their own Noumea to Newcastle DOWNUNDER Cruisers Rally – an evolution of their Port2Port P2P Rally –and also an ICA event. Some have left already. Their Noumea Departure party is this Friday 23 Oct, and their week of fun and culture starts 15 Nov. If you want to know more about this then go to http://www.downunderrally.com/ and an entry form is at http://www.

islandcruising.co.nz/?page_id=3097.  I recommend the passage planning page by Rod Waterhouse at

http://www.downunderrally.com/#!passage-planning--weather-/c92m

To help these rallies I'll concentrate my Weathergram between now and mid- November on these events.

 

TROPICAL TOPICS

KOOPU has brought damaging wind and rain to Philippines and is now slowly working its way northwards along its west coast, and CHAMPI has also turned northwards already so may stay out at sea. While OLAF is this week’s cyclone for the mid North pacific.

During the past week we had an interesting tropical depression form north of Fiji, it went west then south and on Friday was on the verge of being named a tropical cyclone but didn't quite make the grade. It needs gale winds near its centre for at least half a circle.

It has made an interesting jump to the west on Sunday morning local time, as seen at the web site from Fiji Met Service at http://www.met.gov.fj/aifs_prods/65661.

html.

The Weekly rain maps at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif show strong rainfall near the Philippines from KOOPU and further east in CHAMPI, and also around Tuvalu.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ has lost some convective energy now that it has been take away by that tropical depression near Fiji. What is left is expected to have a reasonably quiet week neat Tuvalu and Samoa, with scattered convection over Southern cooks/French Polynesia,

 

STR= Sub-tropical Ridge

The STR is STRONG along around 30 to 35S, and has been creating squash zones of enhanced SE winds and/or southerly swell following fronts and on the northern side of the High cells as they migrate east.

High over Tasmania tonight is expected to travel NE across Tasman Sea and cross northern NZ on Tuesday and then migrate eastwards with a squash zone – mainly of 3m swells- on its north side particularly affecting the Tahiti to Niue route from Thursday to Saturday.

Another HIGH over Tasmania on Thursday is expected to reach northern NZ by Sunday 25 Oct, and then travel east and bring another squash zone to the Tahiti to Niue route next week.

 

Travelling Tahiti to Tonga:

A zone of 3m+ swells from the Southern Ocean affects southern part of this route on Tuesday and Wednesday UTC. Another zone of 3m+ swell, along with some strong SE winds, from a squash zone affects this route from Thursday to Saturday.

 

Between Tropics and NZ:

 

For the All Points Rally:

Early this week there are light winds near Fiji and rough seas off the south of New Caledonia—that may delay some starters.

If you are heading for NZ from New Caledonia/Fiji or Tonga, then the main deciding pointers are the fronts crossing northern NZ. There’s one this week on Thu/Fri 22/23 Oct, and its followed by a period of southerly quarter winds on Friday/Saturday—you should be able to cope with those by going W in southerly winds, SW in SE winds and SE in SW winds.

 

Between Tropics and Australia

For the Downunder Rally (Noumea to Newcastle) Some rough seas just south of New Caledonia and start of Tuesday so departure after that is more comfortable.

A southerly buster is forecast to reach Newcastle around midnight Wednesday and these southerlies may reach as far north as 25S on Wed/Thu maybe Friday, but should be able to be handled with appropriate waypoint diversions.

Strengthening northerly winds are likely offshore Newcastle on Monday and Tuesday 25-27 Oct and then a heat trough is expected to cross Newcastle on Wed 28 Oct possibly with thunderstorms.

AT this stage a Wednesday departure seems to be the most comfortable of the week.

>>>>>> 

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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