 Ocean
Watch
Friday, November 1, 2002
Hurricane’s birth
is death of a trip
My 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. |
