Bob Blog 30 Sep



Compiled Sun 30 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.

Note that there will be NO Weathergram next weekend (7 October).

I shall instead be on holiday in Fiji , so next weathergram is 14 October.


Sea Surface temperature anomalies as at end of September may be seen


The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is now on a steady warming trend. Warmer than normal seas between Mexico and Hawaii have been forming a procession of tropical cyclones. There is a zone of warmer seas from Solomona Islands to Tonga. Temperatures around Australia and the Tasman sea remail below average, a possible indicator of drier than normal conditions in the next month or so. Also this should cool the southwest winds that reach New Zealand.

The Gulf Stream off the east coast of North America and the Kuroshio current off Japan still stand out as warmer than normal.

To see how the annual weather cycle and the seasons are working out, check the average isobar maps from

Average isobars for past 30 days and their anomaly:



The isobar maps show an intense High over that part of  Antarctica which is  south of Australia. The subtropical ridge in the southern hemisphere has intensified during September.

Zooming into the NZ area, the 1010hP (between dark and light blue) isobar has shifted to south of New Zealand. And the 1020 has blossomed from the Aussie Bight to western Tasman Sea. .

AUGUST           image


The last 30 days of rainfall, and its anomoly are seen at



The rain map shows extra convergence around Papua New Guinea and Solomon Islands.

The blue stripes in the North Pacific and Atlantic show the rain tracks of last months cyclones.


The number of tropical features has increased during the past week.

Map of current storms is from


And we had an out-of-season cyclone LUIA in the Solomon Islands:


Image from Bureau of Meteorology.

It has since faded away. Last time we had a cyclone in South Pacific in September was in 1950, Last time we had an out-of-season cyclone was RAQUEL in July 2015

Looking at the weekly rain maps, last week’s shows the rain track of TRAMI across Japan, and LIUA across the Solomon Islands. There is also a resurgence of activity along the ITCZ in the eastern North Pacific.






Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta),currents, STR, and SPCZ. Pink area = lightning likely (high CAPE)

SPCZ=South Pacific Convergence zone.

The SPCZ faded today after a burst of activity last week culminating in the brief formation of TC LIUA. There is still some activity near 13S mainly between 180 and 160E. This activity is shifting southwards and expected to visit Fiji on Wednesday as a passing trough, followed by a Southerly flow between Fiji and NZ on Thursday.

A passing trough over Tahiti is expected to travel east across Tuamotu islands by local Wednesday. Followed by increasing winds from the south-southeast.


Accumulated rainfall for next week from CZ= convergence zone.

Subtropical ridge (STR)

HIGH often over 1030hPa to travel east from 180 to 140W along 30 to 35S. with a squash zone of enhanced SE winds on its northern side. This squash zone is expected to be mainly north of 20S and is worth avoiding.

Between Tropics and Tasman/NZ/Aus.

That trough travelling south over Fiji on Wednesday is expected to morph into a Low lingering near northern NZ on Thursday and Friday, slowly travelling southeastwards. Avoid.

From around Thursday, that trough should have cleared from Fiji, so that a voyage from Fiji to NZ may be OK, but will need to go SW at first in southerly winds.

From Tonga may have to wait until Friday for OK weather for a voyage to NZ.

From New Caledonia to Australia. looks ok to go, but Mon/Tue/wed departures may encounter south to southwest winds for starters.

From Tahiti to Tonga

Avoid the squash zone by staying south of 20S. Anticipate a passing trough along the way early next week.


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

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