Bobgram 22 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 22 December 2024

Seasons Greetings

Sydney-Hobart 1998
A storm formed in Bass Strait during the Sydney-Hobart 1998.
Six sailors died, 70 were injured.
The weather maps as shown at
journals.ametsoc.org/view/journals/wefo/15/5/1520-0434_2000_015_0543_t
abdso_2_0_co_2.xm

The report of the court of Inquiry makes interesting reading
at
www.ussailing.org/wp-content/uploads/2018/01/Sydney-to-Hobart-Race-Cor
oners-Report-1998.pdf

With comments such as
"It's going to be a shit fight in Bass Strait" on page 68

This is a storm that changed the way marine forecasting is done.
From the Court of Inquiry report, recommendation Number 6 on page 21
(for Category One Yacht races) was as follows

6) THAT WEATHER FORECASTS WHICH ARE SPECIFICALLY PROVIDED FOR YACHT
RACING FLEETS CONTAIN:-(a) AS WELL AS THE AVERAGE WINDS EXPECTED, THE
MAXIMUM GUSTS OF WIND THAT ARE LIKELY TO OCCUR; AND (b) AS WELL AS THE
SIGNIFICANT WAVE HEIGHTS EXPECTED, THE MAXIMUM WAVE HEIGHTS THAT ARE
LIKELY TO BE ENCOUNTERED.

Ever since then all marine forecasts issued by the Bureau of
Meteorology in Australia carry a disclaimer:


As for this year's Sydney to Hobart starting on Thursday:
For starters there is expected to be an increasing Northeast wind
making for fast and furious conditions for the maxi Yachts. Then there
is potential for some nasty weather ahead for the majority of the over
100 vessel fleet. A change is being forecast on Friday which could
whip up testing conditions - including 35 plus knots of wind and 4m
seas in Bass Strait.

TROPICS
Hundreds were feared dead after the eye of Category-4 Cyclone Chida
made a direct hit on the impoverished French overseas territory of
Mayotte in the western Indian Ocean. Officials said 90% of the island
nation's buildings were destroyed. Chida went on to leave dozens dead
in Mozambique and neighbouring Malawi.

There is a convective complex in the Coral Sea which is forecast to
deepen on Monday and then weaken on Tuesday then swing off to the
southeast towards Raoul Island.

This system may briefly be named as a tropical cyclone.


WEATHER ZONES
The wind accumulation shows that mid-latitude Low L3 has more wind
than tropical Low L2. Subtropical Low L1 has strong NW winds on its
eastern side. The spot value off the Eden corner this week has a
maximum of 55kt for the Sydney-Hobart.

The South Pacific Convergence zone extends from PNG to South of Tahiti
and is very active this week thanks to an active MJO.

LOWS and HIGHS

Subtropical Low L1 is expected to form south of Niue on Monday out of
a thundery trough that crossed NZ this weekend.

Tropical Low L2 is expected to deepen in Coral Sea on Monday then
travel Se towards Raoul Island and weaken. It might briefly be named
as a tropical cyclone and is expected to bring strong winds and heavy
rain to Vanuatu mid-week.

Low L3 is expected to deepen off New South Wales on Monday and then
travel east along 40S, building a southerly swell over 6m in
mid-Tasman by mid-week. It should then cross central NZ on Boxing Day
and merge with L2 east of NZ continuing east along 40S into next week.
Avoid.

HIGH H1 should form off New South Wales mid -week and move into
central Tasman Sea following L3. It has strong NE winds on its western
side and is expected to be followed by a strong trough reaching Bass
strait early Friday, in time to affect the Sydney-Hobart fleet.

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