Bobgram 19 Oct 2025

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 19 October 2025

The migration

 The nominal start to the cyclone season in 1 November, so this is the time
of the year that yachts set sail from Fiji/Tonga to NZ /Australia

This evening's snap from Marine Traffic shows the migration in mid- flight

This is also a good time to consider the MJO. the madden Julian Oscillation
is the name given to a pulse of extra convection that ripples around the
world from west to east, from the Indian Ocen to the Pacific Ocean. This
takes around 4 to 6 weeks and then repeats.  A good way to measure this
oscillation is via satellite measurements of outgoing radiation.  Cloudy
skies block the OLR giving low measurements (blue), clear skies give high
measurements (yellow).  The way I remember it is: blue is bubbly and yellow
is mellow.

The diagram to use is found at
www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/forca.shtml

The measurement done on 17 Oct shows the next MJO starting off as a blue
area in the Indian ocean.   In the last panel we have the forecast for days
11 to 15 out from 17thOct at end of this month.  By then this MJO is over
the Philippines.   SO early in November it will be in the Pacific, but this
particular MJO episode is looking to be too far north to have much impact on
the South Pacific. So there seems to be little chance of it triggering a
tropical cyclone in the South Pacific.

NOAA has announced that a weak LA NINA has started, triggered by cooler than
normal seas around the eastern equatorial Pacific.  In the South Pacific,
this climate driver allows the subtropical ridge to shift closer to New
Zealand.   This LA NINA has a good chance of fading away by early 2026 and
may have a slight reducing impact of the cyclone risk in the next few
months.  

TROPICS

Two named storms is active tonight

In the past week….

• Japan's Hachijōjima Island was raked in quick succession by typhoons
Halong and Nakri.

• Tropical storm Lorenzo threatened only shipping lanes in the Atlantic

. • Karen became the most northern named storm on record to form in the
Atlantic.

 • Tropical Storm Raymond skirted Mexico.

 WEATHER ZONES

 Rain accumulation this week from Windy.com below shows well defined SPCZ
between Solomon Islands and Samoa thundery showers around an upper low west
of New Caledonia.

Wind accumulation from windy.com below shows a squash zone in the tropics
between New Caledonia and Fiji

LOWS and HIGHS

An upper trough has moved from Australia onto the Coral Sea /New Caledonia
area.  This cooler air is dropping to the surface easing the trade winds
into a lull.  It is also congealing the thundery showers of the SPCZ into a
rampart around this zone that spends the first half of this week mainly over
Vanuatu to east and south of New Caledonia. If in this zone may as well stay
put until it weakens late this week.

HIGH H1 at around 35S and to NE of New Zealand is
quasi-stationary/slow-moving.

FRONTS associated with the disturbed westerlies are expected to visit
 Sydney on Wed 22 and Sun 26 Oct and reach Opua on Friday 24 and Wed 29
October.

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