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

10 November 2013

BOBGRAM issued 10 Nov 2013

WEATHERGRAM
YOTREPS
Issued 10 November 2013

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

XTRA are disabling my bobmcd@xtra.co.nz account every time I send a weathergram blog now. Very inconvenient so I think I'll change the sending address to bob@metbob.com slowly over the next few weeks. Those who have bobmcd@xtra.co.nz white listed on their sailmail or winlink accounts (on list of allowable emails):- please also white list bob@metbob.com , thanks- easiest way to do this is to send an email from your account to bob@metbob.com .

SST: The Sea Surface temperature anomaly is a good indicator as to where the weather may behave 'normally' or 'abnormally'. The latest anomaly map over the South Pacific shows an inter-lace of cool and warm areas along the equator between the dateline and Peru. This is the zone that triggers an El Nino or a La Nina but it isn't quite doing either at present.

There is a zone of 'warmer than normal' covering the region from Solomons across Fiji to Tonga. This might help tropical cyclones to form or offer them a track to follow. Too early to tell, but keep this in mind.

TROPICAL TOPICS
TC HAIYAN was heralded as the world's strongest typhoon of the year before it made landfall in the Philippines, and now the death toll from this storm is estimated to be over 10,000 with over 4 million people being affected by this one day event. It is now losing intensity and turning north and should fade over south China in the next few days.

(Add a couple of 'r's, and then 'Terror' is a meteorologist's middle name.)

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is slowly getting more active and stretches from Solomons to Wallis/Futuna/Samoa to southern French Polynesia, with a few side branch convergence zones CZ. A Low is expected to form in the CZ crossing Southern Cooks this weekend producing a squash zone of reinforced easterly winds near 30S from 140 to 160W early next week.

Sub-tropical Ridge STR
After last week's steady progression of highs and Lows in the mid-latitudes, the STR spent last week travelling south, and is now in its southern setting. This is a pattern sometimes called 'low index' and is expected to continue this week as well, with plenty of room for lows to form between the SPCZ and the STR.

Tasman Sea/NZ.
A Low is now expected to form within the heat trough over Australia and move across 30S on Sunday 17th and deepen near Lord Howe Island early next week. A front associated with its trough is expected to reach New Caledonia by Monday 18 Nov and maybe Northland by Wednesday 20th November, preceded by strong NE winds. Avoid.

Route Briefings
Between tropics and NZ
Try and time your voyage from the tropics so the arrival tine in New Zealand does NOT coincide with a front or strong winds.
The current pattern looks promising- High pressure over NZ from now until Monday 18th Nov are expected to maintain much the same pattern with a flow that is SE/E flow over New Caledonia /Fiji/Tonga and a weaker NE to Opua. Good for departures on Monday and Tuesday.

However it is not expected to last this way for long.
A LOW is expected to move from central Australia to the Lord Howe area on or by Sunday 17 Nov, and may become slow-moving there next week. An associated FRONT is likely to reach New Caledonia by Monday 18 Nov and Northland by Wednesday 20 November. The NE winds ahead of this front may aid your voyage, but not if they get strong. Still too far away to tell exactly.

Since the sailing time for a boat capable of going up to 6 knots in the likely winds for this voyage from tropics to NZ is around 7 days to Opua, a departure on Tuesday 12th or early on 13th may get you to Opua before the front on the 20th, but a later departure may have an encounter with strong winds from that front. This is all still rather hazy, so ask for an update.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
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