Bobgram 4 Jan 2026

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 4 Jan 2026
A review of last month's weather
Here is a link to a YouTube clip giving an animated loop of the isobars and
streamlines
For the month of December youtu.be/GoVdw1VqSZk

Australia had several heatwaves during December 2025. In New Zealand a cold
pool entered the Tasman Sea a few days before Christmas and then fed intense
thunderstorms over the country until a few days after New yea . Intense
winds on 30 Dec produced widespread damage around my place but none in my
village

The 500hPa heights and anomalies shows that prolonged upper low over Tasman
sea late in the month
From http://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_sh_anim.shtml

Sea Surface temperature anomalies from psl.noaa.gov/map/clim/sst.shtml show
that the La Nina cool waters are relaxing. The intense warm pool that was
from Coral sea to New Zealand has shifted east and weakened a little.

Average isobars for past month (below)
From http://www.psl.noaa.gov/map/images/fnl/slp_30b.fnl.html show that the
subtropical ridge in the Southern hemisphere has weakened and turned trough
over New Zealand. The low pressure band over the Aleutian Islands has
weakened.


Pressure anomalies for past month (below)
From https://www.psl.noaa.gov/map/images/fnl/slp_30b.fnl.html show that the
anomaly pressure pattern for December shows the large low breeding area
over New Zealand. The 1010 line has shifted north from Dunedin to
Auckland.


TROPICS
The latest cyclone activity report is at zoom.earth and tropic.ssec.wisc.edu
and Tropical Cyclone Potential is from
http://www.ospo.noaa.gov/products/ocean/tropical/tcfp/
Tropical Cyclone GRANT spent last week crossing the South Indian Ocean.
There is increasing potential for a cyclone to forma around the north coast
of Australia.

WEATHER ZONES

Rain accumulation this week from Windy.com above shows well defined
monsoonal trough over north end of Australia and a track of rain southeast
from Fiji due to a couple of lows. Wet over the Southern Alps due to passing
fronts and mainly dry in the High over north Tasman Sea and North island.
Wind accumulation from windy.com above shows windy areas associated with
low pressures over northern Australia with monsoonal NW winds getting as far
as Solomon Islands and SE winds over the Coral Sea.

Highs and LOWS
Low L1 left New Zealand today and is expected to travel off to the east.
Low L2 is tropical feature that was over Fiji today and is expected to go
southeast. It may deepen between 30 and 40S late in the week.
High H1 now over Chathams is expected to travel off to the east /northeast
at a steady rate.
High H2 now in the Tasman Sea is expected to take its time travelling east
across North Island this week.
A wet and windy monsoonal trough is sitting over north end of Australia and
expected to brew tropical lows L3 over Gulf of Carpentaria and L4 over NW
Australia late this week. Avoid.
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