Bob’s Blog 24 Oct 2021

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 Sunday 24 October 2021


We had a LA NINA episode last summer, and it now looks likely we are heading for another LA NINA episode this coming summer.

See for more details.

During a LA NINA the trade winds are stronger than normal, feeding sun-drenched warm water westwards. This also increases the upwelling around the eastern equatorial pacific (EEP), so that sea surface temperatures are cooler than normal there.

This modifies the rainfall, as shown in this forecast rain map for January to March 2022:


(brown for drier-than-normal and green for wetter-than-normal). The South Pacific Convergence zone SPCZ is likely to shift to south and west of normal, from Coral Sea to northern Tonga to southern Cooks.

Having two LA NINA episodes in a row — a “double-dip” LA NINA is unusual.


Southern Oscillation Index as seen at Bureau of Meteorology website

(based on the normalised pressure difference in hPa between Tahiti and Darwin).


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


RICK is intensifying and expected to make landfall over west coast of Mexico on local Monday.


Weather Zones Mid-week GFS model showing isobars, winds, waves(magenta), Rain (Blue),

STR (Subtropical Ridge), SPCZ (South Pacific Convergence Zone) and CAPE (in pink)


CAPE mid-week as seen by ECMWF and GFS from


SPCZ=South Pacific Convergence zone.

The SPCZ stretches from PNG to Tuvalu to Samoa and drifting from Society Island sto Southern Cooks.

Good trade winds over South Pacific this week.


Rain Accumulation next five days from


Trough over northern NZ tonight should fade away on Monday.

High H1 has been lingering over Chathams area for a few days and should travel slowly northeast this week.

Low L1 east of Tasmania is expected to travel east reaching central NZ by Thursday then northeast across the North Island on Friday, following H1.

High H2 is expected to travel NE to east of South Island late in the week, following L1.

High H3 is expected to travel east across the northern Tasman Sea from Tuesday to Saturday.

Low L2 is expected to travel southeast over Tasmania on Friday.

Avoid arriving at Opua on Monday 1 Nov due passing trough followed by southerlies, or on Wed 3/Thursday 4 Nov due possible strong easterly winds.


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