A Thunderstorm on the horizon.
Photo: Joe Boreland
December 4, 2001
A Captain's Report - Weather Update
This is Rodrigo Olson, captain of the Odyssey.
With the proximity of the summer season in the Southern Hemisphere,
the weather in this part of the world has started to change. As the Inter
Tropical Conversion Zone moves south, the weather becomes more unsettled,
hotter and very humid. The first rain showers of the season mark the
definite end of the dry months. Most notorious besides the oppressive heat,
are the isolated thunderstorms occurring at the end of the day or early
evening bringing torrential rain, high gusty winds and powerful electrical
Besides the isolated thunderstorms, the arriving of the summer season
brings the occurrence of Tropical Cyclones. These storms are characteristic
of all tropical areas of the world, and in the Southern Hemisphere, the
cyclone season starts the beginning of November and finishes the end of
April. Tropical Cyclones are intense low-pressure systems, which in the
Southern Hemisphere have well defined clockwise circulation, with mean
surface winds exceeding 63 knots. They derive their energy from warm
tropical oceans and do not form unless the sea surface is above 26.5 Celsius.
Depending on their strength; they are classified from category 1 to 5, being
category 5 the most severe and destructive (with winds over 155 knots).
The North West coast of Western Australia experiences more severe cyclones
than any other part of the Australian coastline. Several cyclones form each
year, but in average only 2 cross the coast. Most activity is observed from
January to March. While we were still in Darwin, I took the opportunity to
visit the Bureau of Meteorology to gather more information on cyclones and
weather patterns off Western Australia. I was told that this season it is
expected at least 1 tropical cyclone will form off the Northern Territory,
and 60% chance of 2 or 3 cyclone formation. For North Western Australia it
is expected an average season, with around 4 cyclones from which at least 2
might have coastal impact.
It is also known through records that cyclones in Western Australia form in
latitudes between 7' S to 15' S and move off in a WSW to SSW direction,
recurving to the SE between 15'S to 20'S.They move at about 5 to 10 knots in
latitudes above 20'S, 10 to 15 knots north of Shark Bay, and 25 to 45 knots
south of Shark Bay. But one must remember that cyclones are also notoriously
unpredictable and at times they even make loops or backtrack in direction.
On the 27 of November we heard of the first tropical cyclone during our
trip. Tropical Cyclone "Betsy" formed northwest from Cocos Island in the
Indian Ocean, but fortunately too far to pose any threat to us. Most sailors
take cyclones very seriously and would never willingly risk the encounter of
these powerful storms at sea. Several years ago when I was sailing across
the Pacific, we were affected by two hurricanes in French Polynesia. The
first one caught us in Bora- Bora, with winds over 60 knots. The second one,
much stronger and powerful, battered the island of Tahiti and us with winds
exceeding 90 knots. When you experience such a natural phenomenon face to
face and for several hours, you realize how small we are and how powerful
Nature forces can be.
Rodrigo Olson, Captain of the R/V Odyssey.
Photo: Chris Johnson
The weather since we left has been very variable and different each day.
Light winds from all directions, at times calms or overcast, and some
evenings with peculiar thunderstorms. The sea, having been gentle, has
allowed us to make good progress in the right direction. We have been more
or less following the coast, enough offshore to avoid the numerous reefs and
islands that lie off the coast. The waters in this part of the coast are not
very deep as the continental shelf extends well offshore.
Along the way we
have seen numerous sea snakes, some sea birds, few dolphins but no whales.
North and East of Northwest cape and before Shark Bay, we hope to be
picking up the Leewin current, which is a warm ocean current that flows
strongly southward along the Western Australian coast. It is because of this
current that the continental shelf of this part of the coast has the
presence of true corals and tropical marine species. The current is stronger
in autumn, winter and early spring, and slower in the summer months, with
speeds between 1 to 3 knots. It runs along the 100-fathom line, and reaches
past Cape Leewin where it turns east into the Great Australian Bight. Once
we reach Northwest cape, the most prominent landmark of the west coast, the
shore turns more due south, and after Shark Bay, even south southeast as
far as Cape Leewin, where the coast turns to the east. There are about 1,200
sea miles to be covered between Darwin and Shark Bay, our first destination,
which depending on weather conditions, can take us 10 to 14 days. Southwest
of Shark Bay there is an area reported by our Townsend charts in which the
old whalers used to hunt sperm whales. We hope to be exploring this area, as
well as exploring the ruins of several dilapidated whaling stations along
We look forward to arriving in Shark Bay and to get to see more of this
amazing and little populated coastline, as well as to meeting up with our
legendary friends, the magnificent sperm whales.
Log by Rodrigo Olson