Ocean Watch
By Susan Scott
Hurricane’s birth
is death of a tripMy friend from New Mexico e-mailed recently with exciting news. She and her husband had received a rare invitation from the Nature Conservancy to visit Palmyra, a remote tropical island renowned for its marine life.
The couple was to meet biologists and several other nature lovers in Honolulu, and then take a private flight to the atoll, located about 1,000 miles south of Hawaii.
Everything seemed to be going fine, but just as people were about to board the charter plane, two fearsome bandits appeared out of nowhere and held them up. These bad guys were so scary, and so unpredictable, that the long-planned, highly anticipated Palmyra trip ground to a screeching halt.
These two outlaws' names were Lowell and Huko, Lowell being a tropical depression, Huko a tropical storm. Both besieged the ocean between Hawaii and Palmyra last week, threatening to become hurricanes.
The first stage of hurricane development is a tropical depression, like Lowell. Tropical depressions begin over tropical waters and must have several other natural ingredients to form. One is a surface temperature of 80 degrees or warmer. This high temperature allows a large amount of water to evaporate, adding moisture to the air. It is this heat and humidity that supply much of the energy for a storm's development.
Tropical depressions also need swirling winds at low levels and light winds at upper levels.
When all these conditions are met, and the wind moves in a circle at least 23 knots (one knot equals 1.15 miles per hour), we have a tropical depression.
As the warm, wet air of a tropical depression continues to rise upward in a column, the air pressure inside drops and wind speeds increase. A depression gets upgraded to a tropical storm, like Huko, when winds range from 23 to 73 knots.
If strong surface winds blow into an area hosting a tropical storm, and the swirling air reaches 74 knots or more, a hurricane is born.
Not everyone calls these storms hurricanes. The word hurricane comes from Huracan, a god of evil to ancient people in Central America. We use the term today for storms in the Atlantic and Eastern Pacific Oceans. Australians, however, call hurricanes willy-willies, and in the Philippines, people speak of baguios when discussing these big storms.
In the western Pacific and China Sea, people refer to hurricanes as typhoons, a word that comes from the Cantonese tai-fung, meaning great wind. In Bangladesh, Pakistan, India and Australia, hurricanes are known as cyclones.
Tropical depressions, storms and hurricanes aren't particularly rare around Hawaii, but they don't often ambush us this late in the fall. By November we Hawaii residents are usually breathing a sigh of relief that we made it unscathed through another hurricane season.
But we shouldn't relax yet. Hawaii's hurricane season runs from June through November, because that's when our water temperatures are warmest.
Most tropical depressions and tropical storms peter out, but tropical storm Huko became Hurricane Huko, and the Palmyra trip was canceled.
Everyone was sorely disappointed but that's life in the tropics. We are host to -- and sometimes held hostage by -- the greatest storms on Earth.
Marine science writer Susan Scott can be reached at http://www.susanscott.net.
