Bob Blog 3 Sep

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 3 Sep 2023

A review of last month's weather
Here is a link to a YouTube clip giving an animated loop of the isobars and
streamlines in the South Pacific for the last month at youtu.be/XOKGeaFSW3k

August shows several bursts from the Southern Ocean onto New Zealand,
showing that El Nino-type weather patterns are now occurring. Sometimes lows
lingered over northern NZ due to blocking Highs south of Tahiti. This is a
continuation of the dominate pattern in July. Here is an example of the
August pattern (8 August


Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml

Sea temperature anomalies are much the same as they were last month. Even
the El Nino warm patch is much the same. After the warmest July on the
global record, August is still record- breaking but not quite as intense.


Average isobars for past month (below)
Subtropical ridges have relaxed. The Asian monsoon is travelling east as per
normal. The trough area around New Zealand has faded.

Pressure anomalies for past month (below)
Higher than normal over Australia and NZ, and lower than normal over SE
Pacific and South America. Not much change in the Northern Hemisphere but
lower than normal pressure in the monsoon over easter Asia.

Zooming into the NZ area
Relaxing of the trough around NZ. A subtle southward shift in the
subtropical ridge. South-westerly isobars now cover NZ.

TROPICS
The South Pacific Convergence zone is expected to stay north from Solomons
to northern Vanuatu to Samoa. There is also a trough /convergence zone
mainly lingering over Austral Islands.

Tahiti to Tonga? Good winds for this voyage this week, but maybe some 3m
swells around Tahiti.

HIGHS and LOWS

HIGH H1 near Chatham Islands east of NZ is a blocking High and expected to
travel slowly NE/

Low L1 is a blocked Low and is being directed off to the south and
weakening. By end of the week, it is expected to be replaced by a trough
from Tasmania forming a new Low that is expected to cross the South Island
late in the week, then another over all of NZ early next week.

Tropics to NZ: look Ok this week, but avoid arrival on Mon/Tue 11/12
September

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