Bobgram 11 Dec

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 11 Jan 2026
Last year's New Zealand weather.
Illustrated version has a time-latitude plot of the air temperature measured
over a north-south slice of Aotearoa/ NZ as it travelled through 2025.

The land silhouette is provided to help relate the latitude axis to your
place. It clearly shows temperature is cooler further south and during
winter. This time section makes a "bar-code" graph which reveals the annual
trend and the daily variation. It gives a rough indication of the extremes
and provides a visual image for quick comparison with any another year to
see seasonal variations.
Here below is what we had in 2024.
Compared with 2024, 2025 was cooler with some blue getting to the far north
in winter.

Looking at a similar diagram for the barometric air pressure provides a
graph that combines all the daily weather maps into one image. This produces
a more random looking barcode. The yellow and red lines correspond to
passing HIGHS on the weather map, and the blues show the LOWS or
depressions/storms. The scale is in Pascals, divide this by 100 to get
hectoPascals/millibar.

This has more red in it than last year, with the months from April to August
being mostly marked with passing Highs on the weather map.
The rain image below is probably the most interesting as it highlights the
dry periods in Northland last February to April, wetness from May to October
and dry from October to mid-December, then a wet Christmas/New year.

Bob McDavitt
TROPICS

Tropical Cyclone GRANT, after crossing almost the entire Southern Indian
Ocean , faded on approach to Madagascar.
Iggy and Jenna formed south of Java and faded quickly. Dudzai is currently
in South Indian Ocea,
Also KOJI formed yesterday and is now fading after making landfall in
Queensland,

WEATHER ZONES
Weather Zones Mid-week GFS model showing isobars, winds, waves (purple),
rain (red), MT (Monsoonal trough), STR (Subtropical Ridge), SPCZ (South
Pacific Convergence Zone) CZ (Convergence Zone)

Rain accumulation this week from Windy.com above shows well defined
monsoonal trough where the South Pacific convergence zone usually sits.
There are NW winds on the northern side of this trough and northerly winds
across the equator as far east as 180. If these winds get further east then
they may disrupt the cooler than normal surface water that marks the current
weak La Nina.


Wind accumulation from windy.com shows bursts of wind associated with the
three tropical lows and another well to east-southeast of New Zealand..

Highs and LOWS
A trough is crossing New Zealand tonight/early Monday, followed by High H1
with a few days of dry weather. Then High H1 travels steadily off to the
east along around 40S.
Three tropical lows are expected to form along the SPCZ/Monsoonal trough
this week. L1 affecting Tonga, L2 affecting Vanuatu and New Caledonia
(maybe travelling south next week), and L3 the remains of TC KOJI settling
in as a heat trough over central Oz..

A heat wave is expected to continue over Australia, with the peak heat
travelling to NW to north parts of WA between Broome and Karratha by end of
the week.
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Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or text 64277762212.
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