Bobgram 26 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 26 October 2025

The storm of 23 Oct
A trajectory analysis of air arriving in New Zealand on Thursday 23 October,
as seen at www.ready.noaa.gov
shows the collision between cold air from the south with warm air form the
north.
Squashed isotherms produce squashed isobars.

Indeed the isobars clustered together around a 958hPa low and over Kiwiland.


The pressure difference between Auckland (1012hPa) and Invercargill (970
hPa) known as Z1 or New Zealand's primary zonal parameter was 42 hPa .
The resulting wind damage was widespread and devasting:

www.nzherald.co.nz/nz/north-canterbury-farmers-begin-major-cleanup-after-des
tructive-storm/2VZAV2OPGRE65BGJNY7FPXOCGA/

www.odt.co.nz/southland/25000-without-power-south

The thermal clash has recently been abnormal, and this can be traced back to
the Sudden stratospheric warming in September.
Tonight, there is a polar jet stretching due north off Antarctica as far
north as Tasmania. It is squeezing the isobars closer together around a Low
in the Tasman sea.



TROPICS
In the past week..
. Tropical Storm Fengshen killed seven in the central Philippines from
flooding and then drenched China's Hainan Island and central Vietnam.
. Tropical Storm Melissa formed over the central Caribbean
.Cheng churned in the Indian Ocean

WEATHER ZONES
Rain accumulation this week from Windy.com below shows well defined SPCZ
zone in the tropics mainly along 12S .
Wind accumulation from windy.com below shows the trade winds to the north
and the roaring 40s to the south with subtropical ridge in-between.
LOWS and HIGHS
Low L1 in Tasman Sea is being energized by that Polar yet from Antarctica.
The thermal clash should bring more west to NW gales to NZ on Monday, (a
public holiday).
After that on Wednesday and Thursday the High H1 is expected to travel
quickly across Tasman Sea and northern NZ, as Low L2 deepens east of
Brisbane.

Low L2 is expected to travel quickly along around 30S past NZ on Thursday.

The High H2 is expected to cross the Tasman Sea NZ area in a more sedate
fashion from Sat 1 Nov to Tue 4 Nov and maybe with a lingering influence
until Thursday 6 Nov..but the models differ about that after 3 Nov.
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