Bob log 4 Oct

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.

Compiled Sun 24 Oct 2020


Sea Surface temperature anomalies can be seen at

Early October (below)


La NINA kicked in mildly during September. Eastern equatorial Pacific continues a trend to COOL and the west of the South Pacific continues to be warmer than normal This means the coming cyclone season is likely to be less than normal for Coos Island s and French Polynesia, but it may be more active near 180 longitude (places such as Fiji).Also the South Pacific ridge line is likely to shift south.

The North Pacific and Atlantic have warmed between 30 and 50N but this may be seasonal.

To see how the annual weather cycle and the seasons are working out, we can check the average isobar maps for past 30 days and their anomaly from

Average isobars for past few weeks


Pressure anomolies for past few weeks


The monsoon is on schedule. The southern hemisphere sub-tropical ridges has strengthened, an d the northern hemisphere subtropical ridge has widened.

Zooming into the NZ area, and comparing monthly anomalies from last month with now, shows that the sub-tropical ridge has shifted north over NZ (as per a normal July), but strangely has intensified over Australia.

Last month Below



Last few weeks (above)

The ridge near NZ has strengthened to over 1020hPa and expanded south to 40S. The Antarctic high has weakened. .


The Tropics

The latest cyclone activity report is at and Tropical Cyclone Potential is from

Two active tropical depressions today. GAMMA has made landfall in Mexico and MARIE is travelling NW in the North Pacific.

Also some high potential near Philippines, and medium potential around central America and mid-Atlantic.



Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta), Rain (Blue), CAPE (pink), STR, and SPCZ.


Predict wind CAPE mid-week gives two possibilities for SPCZ


SPCZ=South Pacific Convergence zone.

SPCZ is moderate and from Solomon Islands to Fiji to Samoa.

Passing trough over Fiji area on Mon /Tues, travelling off to SE on Thursday /Friday.

Squash zone on Mon/Tues between NZ and New Caledonia due to strong pressure gradient between a High (to south ) and low (to north) with main wind and swell at 30S from 180 to 170E.

Accumulated rainfall for next week from


Subtropical ridge (STR)

HIGH 1032hPa over northern Z on Mon travelling east along 30S on Tues/wed.

New High moving off Tasmania on wed and traveling E to central NZ on Friday, followed by a NW to W trough.

Tasman troughs

Front with strong westerlies over South Island on Mon. Another Front on Tues followed by SW winds Tuesday, and southerly on Wednesday/Thursday as that low from Fiji travels to SE of eastern NZ.


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