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LatestPhoto
A Thunderstorm on the horizon.
Photo: Joe Boreland

December 4, 2001
A Captain's Report - Weather Update
  Real Audio
  28k


Log Transcript

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 storms.

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.

LatestPhoto
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 the coast.

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

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