Bob Blog 22Sep

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 22 September 2024

The Ozone layer

Spring is also the Antarctic ozone hole season,

During the southern winter the Southern Polar Vortex was highly
disrupted and consequently the 2024 ozone hole development began
relatively late.. The evolution of the 2024 ozone hole so far is
similar to that observed in 2022, as shown in the chart above.

There was a larger than normal Ozone hole in 2023.. it also lasted
longer than normal. This is thought to be a consequence of the extra
water vapour in the stratosphere from the explosive volcanic=c
eruption in Tonga in January 2022 with a plume of 53km up into the
atmosphere.

The Ozone hole is formed when direct sunlight shines into the polar
atmosphere. During the dark of winter chemical pollutants such as CFC
build in intensity , and when the sunlight returns the UV reacts with
these pollutants o deplete ozone and build the ozone hole.

However, when the polar vortex is weak, a sit was at times last
winter, with higher temperatures and slower winds than usual in the
stratosphere, the ozone depletion process is weaker, leading to ozone
columns above 220 dobson units (DU), the threshold value used to
define the Antarctic ozone hole.

According to an analysis by NASA's Earth Observatory, Antarctica
experienced two rare sudden stratospheric warming events in July and
August 2024 when temperatures in the stratosphere jumped 15ºC and 17ºC
respectively.

As a result, the southern hemisphere polar vortex was elongated and
with weakened winds, as opposed to the circular, cold and fast winds
conditions that favour ozone depletion, seen for example in 2023.

Instead of the typical behaviour, the ozone hole this year didn't
develop until the end of August.

More can be found at www.facebook.com/watch?v=1056948995791531

TROPICS
There are no named storms tonight. Remnants of Typhoon Yagi took
another 226 lives in Myanmar. • Typhoon Bebinca lashed Shanghai with
the highest winds and heaviest rains since Typhoon Gloria struck in
1949. Weaker Tropical Storm Pulasan took a more southerly course days
later. • Tropical Storm Lleana drenched southern Baja California,
while Tropical Storm Gordon churned the central Atlantic Ocean.

WEATHER ZONES
The South Pacific Convergence zone is sitting over Solomon Islands and
extends to Tuvalu and Tokelau then southeast to Southern Cooks.
Another convergence zone or trough is sitting over southern parts of
French Polynesia.

The wind accumulation map shows the trade winds may get strong at
times thru the Fiji passages around the Niua Islands in northern Tonga
and about southern parts of French Polynesia (avoid), and Coral Sea
may be OK enough for sailing westwards.
This map shows the average position of the light winds of the
subtropical ridge near 25S and the extent of the disturbed westerlies.
A small trough is expected to form off Sydney around Thursday/Friday
(avoid) and deepen as it crosses the Tasman and reaches NZ around 3 /4
October.

HIGHS and LOWS

HIGH H1 remains slow moving well south of Tahiti.

Over New Zealand a trough is crossing on Monday/Tuesday deepening into
L1 travelling off to the SE.
A brief ridge with H2 is expected on Wednesday,
then another broad trough on Thursday and Friday followed by the
ridge of H3 over the weekend.

It looks OK to depart from the tropics and get to NZ, so long as you
avoid the rough stuff near NZ on 26/27 September, and maybe 3 and 4
October.

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If you would like more details about your voyage, then check
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Weathergram archive (with translator) is at
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Contact is bob@metbob.com or text 64277762212.
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