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

06 October 2013

BOBGRAM issued 6 Oct 2013

Issued 06 October 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.

When to head out of the tropics?
Well the chances of encountering some nasty weather in the tropics is rather low at present and gradually increasing to be not worth the risk from around mid-December. Many Insurance companies do not cover weather damage in the South Pacific tropics from 1 November so that many cruising sailors leave by then—however if you wish to hang around for a few more weeks (because there are still a few cold outbreaks reaching NZ and South Australia) then, on average, there isn't much change in the risk during that time.

If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see

Those who are seeking access to a weather map with isobars and fronts and convergence zones that can be down loaded via Internet can request one in FLEET code by sending an e-mail to, no subject needed, with the message "SEND nadi-fleetcode". To be able to view this map, save the number-table in it to a *.txt file and then open this with PhysPlot- You will need to FIRSTLY download and install PhysPlot from

I shall supply more information regarding web sites for checking the weather models next week.


In East Asia TC FITOW is taking a track across northern Taiwan and into China. Following it is TC DANAS but this cyclone is expected to re-curve to the northeast and move onto Japan. In the Gulf of Mexico tropical Depression KAREN is expected to move onto southern states of USA, full of rain but wind is easing.


South Pacific Convergence Zone SPCZ
The SPCZ is active from Solomons to just NW of Fiji. During Fiji's Independence day holiday on Thursday 10 Oct the zone is expected to cross Fiji, and then on Friday a low is expected to deepen rapidly about and to south of Tonga, moving off to the SE. Avoid.
There is another convergence zone which is active mainly along 10S from Tuvalu to Northern Cooks. This zone is a mirror of the ITCZ that tends to form for a few weeks around the equinox and is expected to remain active this week, staying north of 11S.

Sub-tropical Ridge STR
The STR is expected to be north of its normal position this week, and that means a week of weak trade winds.
The high that is over eastern Australia on Wednesday 9 Oct is expected to move east across the Tasman Sea along around 30S and fade away just to south of New Caledonia by Fri 11 October. This is expected to be followed by another High along 30S from Sat 12 Oct and that High is likely to spread out, making mainly light winds in the tropics.

NZ/Tasman Sea

This area continues to have a period of unsettled weather with passing troughs. A Low is expected to form in the Tasman Sea on Monday and cross the North Island during Tuesday/Wednesday, deepening as it tracks to the southeast.
Another Low is expected to form on a cold front as it crosses the South Island on Friday 12 Oct. This Low should cross northern North Island on Saturday 12 Oct.

Route Briefings

Tahiti to Tonga:
Trough is expected to affect Niue on or around Tues 8 Oct and another over Tonga and Niue around Friday 11 Oct followed by a rare period of W/SW winds there on Sat 12 Oct UTC. Otherwise expect light winds this week.

Between tropics and NZ
The southerly flow in the NZ/Tasman area following the low on Tuesday makes for a period of headwinds for anyone trying to sail from New Caledonia/Vanuatu/Fiji mid to late this week. Not Good.
Those trying to get from Tonga to NZ may have a passable voyage with a departure on Wed 9 October, skirting around weather systems.

See my yotpak at for terms used.
Weathergram with graphics is
Weathergram text only and translator is
Feedback to

No comments:

Blog Archive