Bobgram

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 12 October 2025

The coming cyclone season

NIWA of NZ have issued their annual outlook for the coming cyclone season.

The main tropical climate driver at work is a "weak La Nina" pattern. Thia is likely to be augmented by the recent Stratospheric warming which may bring more wind to the Tasman Sea area until December, perhaps leading to stronger shearing forces in the tropics, which tend to prevent tropical cyclones from "winding up".

Here is NIWA's Cyclone forecast-- fewer cyclones than normal.
Greatest risk is in the Vanuatu /New Caledonian area with 3-4 cyclones likely.

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See www.euronews.com/green/2025/10/08/

TROPICS


One named storm is active tonight

In the past week….

•Hurricane Priscilla lashed western Mexico with pounding surf and strong winds before its remnants drenched northwestern Mexico and the southwestern United States.

• The northern Philippines and far southern China were lashed by Typhoon Matmo.

• Category-4 Halong passed just off eastern Japan.

• The Leeward Islands were brushed by strengthening Hurricane Jerry.

• Category-1 Cyclone Shakhti churned the northern Arabian Sea.

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 below shows well defined SPCZ between Solomon Islands and Samoa and another convergence zone between Loyalty Islands and Fiji.

Wind accumulation from windy.com below shows some squash zones in the tropics one between New Caledonia and south of Fiji.

LOWS and HIGHS

HIGH H1 at 35S south of French Polynesia is moving off to the east allowing a procession of weather systems to flow eastwards this week.

Front associated with LOW L1 in this procession is crossing North Island on Tuesday and then travelling off to the southeast.

Another Low is expected to travel from Southern Ocean to the NE in wake of L1, reaching Chathams area by Friday, and maybe bring a brief southerly change to Northland next Sunday night.

HIGH H2 should cross northern NZ on Thursday to Saturday bringing a lull along 30S S

Next front across Northern NZ is expected on Tuesday or Wednesday 21 or 22 October.

One model is starting to have the idea of forming a tropical trough in the Coral Sea late this week and taking this to northern NZ mid next week. So far this is only an idea, but it might grow to be a threat so is a risk.

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If you would like more details about your voyage, check metbob.com
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com
(subscribe/unsubscribe at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or text 64277762212.
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Bobgram

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 05 October  2025

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 youtu.be/l4EARdhOSlo
Lows crossed NZ on12 and 24-25, with several stormy fronts in-between
The Low on 12 September t was especially squally and thundery:
The 500hPa heights and anomalies shows these Lows.
at http://www.cpc.ncep.noaa.gov/products/intraseasonal/z500_sh_anim.shtml

Sea Surface temperature anomalies  from psl.noaa.gov/map/clim/sst.shtml
The North Pacific "blob" is no longer as intense as it was in August.  North
Atlantic has warmed.  The warm area between Java and West Australia is a
NEGATIVE IOD (Indian Ocean Dipole)  
This evening's satellite and radar imagery shows this negative IOD at work

There was a sudden stratospheric warning over that part of Antarctica south
of Australia during past few weeks and this is likely to trigger outbreaks
of cold air due to a weak polar vortex. The parameter I use to watch this is
not being updated by NOAA at present due to "US Government shutdown".

TROPICS

Tonight there are 5 named storms.

In the past few weeks…
• Typhoon Bualoi left 20 people dead in the Philippines before unleashing
days of heavy rain in Vietnam, killing an additional 29.
 • Remnants of Hurricane Gabrielle brought high winds to Portugal, then
triggered flash flooding in eastern and southern Spain.
 • Hurricane Imelda sent pounding surf into the U.S. East Coast, while
Tropical Storm Octavia formed briefly off western Mexico.
• An unnamed tropical storm drenched India's central Bay of Bengal coast.

WEATHER ZONES
 Rain accumulation this week from Windy.com below shows well defined SPCZ
between Solomon Islands and Samoa  and almost drifting south onto Fiji. 
Also a passing trough for Minerva .

Wind accumulation from windy.com below shows some squash zones in the
tropics one to north of Fiji and one in the Coral Sea.  The strong winds
southeast of French Polynesia are associated with a passing trough.  Ther
strong wind trails near Philippines and west of Mexico are associated with
tropical cyclones.

LOWS and HIGHS

Front associated with LOW L1 is crossing New Zealand on Monday and then
travelling off to the southeast.
 HIGH H1 is travelling east along around 30S and crossing northern NZ on
Tuesday/Wednesday.
A warm front is expected across Northern NZ on Sunday 12 Oct  followed by a
cold front around Wed 15 Oct.

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If you would like more details about your voyage, check metbob.com
Or Facebook at /www.facebook.com/metbobnz/
Weathergram with graphics is at metbob.wordpress.com
(subscribe/unsubscribe at bottom).
Weathergram archive (with translator) is at weathergram.blogspot.co.nz.
Contact is bob@metbob.com or text 64277762212.
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