Bobgram 1 Sep 2024

Bob Blog 1 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 1 September 2024
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/h0FhIw4kZzs

The main pattern for August was a migratory HIGH travelling east along
around 25 to 35S followed by a trough or two, sometime three with
disturbed westerly wind south of 40S.

The tropics in the South Pacific were quiet.

The Kuroshio current has spread out into the north Pacific. The
equatorial Atlantic remains warmer than normal. The cool seas of a LA
NINA are spreading westwards from Galapagos to the dateline along the
equator.

During August the Monsoon spread east across Asia.
and the subtropical ridge in northern hemisphere weakened.
An equatorial trough developed in the mid Pacific.
The anomaly pressure pattern for August shows ridging over North
America,
Higher than expected pressures accompanying the Asian Monsoon,
and lower pressures than normal in the southern roaring 40s but for
high pressures around South America.

The roaring 40s have travelled northwards onto the South Island.
The 1015 line has shifted from near Campbell Island to near
Christchurch.

TROPICS
Powerful Typhoon Shanshan lashed Japan's southernmost islands with up
to Category-4 force before the weakened storm later caused damage and
severe flooding to Kyushu Island. . Hawaii's Big Island received flash
flooding and some wind damage from Hurricane Hone, which passed just
to the south. ASNA is near Yemen.

WEATHER ZONES
The South Pacific Convergence zone is sitting over Solomon Islands and
extends to Rotuma and Samoa and then to the southeast across Southern
Cooks. A trough and low L1 to south of Southern Cooks are moving a
windy rain band southward, followed by a lull in the trade winds.
Mostly OK this week for sailing to the west.

HIGHS and LOWS

HIGH H1 has been blocking movement south of Tahiti.

Low L2 is a secondary travelling quickly eastwards along around 45 to
50 S. Associated trough is expected to bring a cold southerly change
to NZ on Tuesday/Wednesday. It's primary Low is in the Southern Ocean.
Following that trough there is expected to be a burst of southwest
swell to over 5 significant metre sin the Tasman Sea. This should
travel north with 3+ m swells reaching Fiji on Thursday. Avoid. Low
L1.

For New Caledonia: The trough associated with L2 is expected to bring
a southerly change late Tuesday. The HIGH H2 moving along 30S into the
Tasman Sea after L2 is expected to develop a squash zone of strong SE
winds near New Caledonia and in the Coral Sea from Wednesday to
Saturday. Avoid.

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