Bob McDavitt's ideas for sailing weather around the South pacific

03 December 2023

Bob Blog 3 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 Sunday 3 December 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

During November the South Pacific weather pattern was something like the
game called FROGGER (available at
With Large trucks being the HIGHS migrating from west to east , from south
of Australia across the Tasman Sea and then stalling east of New Zealand.
The more nimble low systems are like the frogs trying to get from north to
south or south to north sometimes succeeding by sidestepping between the
and sometimes being squashed. This rhythm is the typical spring pattern a
mix of pattern and chaos.

However El Nino is kicking in, along with a positive Indian Ocean Dipole.
The combined impact is to make a breeding ground for tropical lows near 5 to
10S and 170 E to 170W.

During November this only activated once around mid-month
And a similar pattern is happening this weekend.
The warmer than normal area that has been around NZ for much of this year is
getting smaller.

Average isobars for past month : The Siberian HIGH has developed quickly in
November. In the Southern Hemisphere, the subtropical ridge has shifted into
the Australian Bight and a heat trough has developed over mainland

Pressure anomalies for past month : Falling pressures over Russia and rising
pressures over the roaring 40s in the Southern Hemisphere. Note the tendril
of low pressure from Fiji towards New Zealand,.

Zooming into the NZ area: The 1015 isobar has shifted south across

RAMON appeared briefly in the NE Pacific and MICHAUNG is now fading off
Depression92P is building slowly near the Solomon Islands.
It has a twin just north of the equator, defying the rule that rotating
winds are impossible at the equator:
The MJO, a burst of extra energy in the tropics, is expected to enter the
western Pacific over next few weeks.

The South Pacific Convergence zone is building especially with Tropical
depression 92P near Solomons.
This may become a cyclone and travel SW into Coral Sea, and maybe Tasman Sea
next week. AVOID.
HIGH H1 well to east of NZ and south of Tahiti is acting as a block.
It should be replaced by HIGH H2 by end of the week.
LOW L1 crossed North Island on Sunday and is expected to linger to NE of NZ
until mid-week and then travel off to the southeast.
Associated trough is expected to cross Tonga around local Friday.
High H3 should form in Tasman Sea by mid-week and cross central NZ this
A trough from Southern Ocean is expected to enter South Tasman Sea by Friday
and cross the South Island on Saturday followed by a trough and southerly
change early next week.
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