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

02 September 2018

Bob Blog 2 Aep 2018



Compiled Sun 02 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.


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

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is now on a steady warming trend. Temperatures around Australia to New Zealand are becoming below normal, a possible indicator of drier than normal conditions in the next month or so.

The Gulf Stream off the east coast of North America and the Kuroshio current off Japan still stand out as warmer than normal.  These may help steer tropical features away to the northeast.

Warm anomalies continue off west side of Mexico to Hawaii indicating a busy cyclone season for next few months.


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 that subtropical ridge in the southern hemisphere is looking robust, as are the North Atlantic and Northeast Pacific HIGHS. The August lows in the Southern Ocean have been favouring three positions: Tasman Sea, SW of South America, and SE of South America.

Lower than normal pressures between Europe and Philippines show a more active monsoon. 

Zooming into the NZ area, the 1010hP (between dark and light blue) isobar has shifted from Christchurch to Gisborne.  And the 1015 has retreated off Tonga.  This explains the increase in westerly winds onto western NZ, and can be taken as an early start to SPRING weather patterns. Not much change around Australia .


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

The rain map shows extra convergence in the ITCZ from Bangladesh to Philippines , and across  the North Pacific Ocean, but it has been drier than normal over the Caribbean..

In the Southern Hemisphere a large dry region stretches from Australia to Vanuatu/Fiji.. It seems that the SPCZ has shifted northwards and estwards (an El Nino trait).

In summary, it seems that, although the atmospheric and oceanic parameters are “neutral” at present, as seen in my last week’s blog, there are also some signs of an El NINO weather pattern.



We have reached the time of the year when cyclones cluster, as is happening this week in the northeast Pacific Ocean. 

 For Map of current storms see

There is MIRIAM, NORMAN , and OLIVIA in NE Pacific, FLORENCE in north Atlantic, and JEBI in NW Pacific.

NORMAN is expected to sideswipe Hawaii later this week.

And JEBI is expected to visit Japan this week


Looking at the weekly rain maps we can see that the Asian monsoon is active over south China and the Philippines/Indonesia area, and the ITCZ is active across the northeast  Pacific and around Panama. South Pacific Convergence zone is weak and further east than normal.




SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from PNG to the Tuvalu/Tokelau area this week.

Passing trough over southern Vanuatu on Monday and Tuesday is expected to extend SE on Wednesday into a trough southwest of Fiji, the on Thursday turn into a low south of Fiji that then should go SSE to east of NZ.

Trough is expected to form over Tahiti area by local Tuesday, the convergence zone associated with this feature is expected to visit Tuamotu Archipelago to Gambier group around local Wednesday. 


Subtropical ridge (STR)

Large High 1035+ at 35S to south of Tahiti should fade and travel east by end of the week.  The squash zone of enhanced easterly winds between it and the Low over Tahiti should peak around mid-week with strong wind and large swells affecting Southern Cooks.  Avoid.

HIGH travelling east across Tasmania on Monday should skirt around south end of NZ on Tuesday and then travel east along 45S to east of NZ on Wednesday.  Squash zone between this high and Lows to east of the North Island should bring a classic “olde man southerly” to central NZ from Monday night until Thursday.


Around Tasman Sea, NZ.

High pressures in central Tasman sea this week should ensure good voyages from New Caledonia to Queensland. Traffic going from Australia to NZ may need to get to at least 37S to find a way eastward.

Low is expected to be crossing North island don Monday followed by three days of strong SE winds.  Conditions should be OK again around Friday or Saturday for departing Northland, As for sailing to NZ from tropics, nope, too much southerly this week.


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

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