|Published Tuesday, May 23, 2000, in the San Jose Mercury
BY JAN NULL
Special to the Mercury News
With the Atlantic hurricane season beginning June 1, it's a good time to look at this
awesome and destructive natural force.
Q. What's the difference between hurricanes, typhoons and cyclones?
A. Just as in real estate, the difference is location, location, location. They are
exactly the same meteorological phenomenon -- a tropical cyclone, or spiraling storm, with
sustained wind speeds of at least 74 mph.
These storms are called hurricanes when they occur in the Atlantic, Caribbean or eastern
Pacific ocean. The term comes from a Caribbean Indian storm god, Huracan.
In the Western Pacific, tropical cyclones are called typhoons from the Cantonese term tai
fung, or great wind, and from Typhon, a gigantic monster in Greek mythology whose name
These same storms are called cyclones in the Indian Ocean. The word derives from the Greek
term kyklos, or circle.
There are many local names for these monster storms as well. One of my favorites is
along the west coast of Mexico, where these storms sometimes are called cordonazo de San
Francisco, or ``lash of St. Francis.'' This name originates from the strong southerly
winds that can lash out with death and destruction along the coast near the time of the
Oct. 4 Feast of St. Francis.
Q. What are tropical cyclones?
A. They are intense areas of low pressure in the tropics. Just as water flows
downhill, warm, moist air is drawn rapidly inward from areas of higher pressure to the
centers of these lows. Due to the Coriolis Force, they spiral counterclockwise in the
Northern Hemisphere and clockwise in the Southern Hemisphere. This creates the strong
winds that are the cyclone's trademark. The warm air, which derives much of its energy
from the warm tropical ocean waters, rises high into the atmosphere and develops into huge
bands of thunderstorms.
When a tropical cyclone's winds blow at less than 39 mph it is called a tropical
depression. Winds of 39 to 73 mph qualify it as a tropical storm, and at 74 mph or greater
it becomes a hurricane. Hurricanes are rated for damage potential using the Saffir-Simpson
scale, which is based on wind speed. On this scale, Category 1 hurricanes have winds of 74
to 95 mph, Category 2 are 96 to 100 mph, Category 3 are 111 to 130 mph, Category 4 are 131
to 155 mph and Category 5 hurricanes have winds of more than 155 mph.
Category 4 and 5 storms are far more deadly and devastating than lesser categories, but
they also are relatively rare. Since 1900 only 13 Category 4 storms and three Category 5s
have made landfall in the United States.
Q. What makes hurricanes so dangerous?
A. It's the flooding more than the winds. About four times more people are killed by
hurricane-induced flooding than by the wind. Six to 12 inches of rain commonly fall as a
hurricane moves inland. Coastal areas also are susceptible to flooding from storm
surges -- a combination of water piled up by the hurricane's winds and a rise in sea level
because of the extremely low barometric pressure associated with tropical storms. The
surge inundates coastal areas that are often densely populated and difficult to evacuate.
It can range from five feet deep in a Category 1 storm to more than 18 feet with a
Hurricanes also spawn tornadoes, spiraling storms that are much smaller but more intense
as they move inland.
Q. When are these storms most likely to occur?
A. Like the names, this, too, depends on location. In the Atlantic and Caribbean,
the official hurricane season begins June 1 and lasts until Nov. 30. Occasionally, a storm
will occur out of season. Notably, Hurricane Arlene showed up early, intensifying to
hurricane strength May 6, 1981, and Lili hung around almost until Christmas with
hurricane-force winds as late as Dec. 22, 1994. The Atlantic season peaks in early
The season in the Northeastern Pacific runs from around May 15 until Nov. 30, with an
early September peak in activity like the one in the Atlantic. In the northwest Pacific,
the typhoon season is year-round with the highest probability of storms around Sept. 1 and
the lowest about March 1. And the north Indian Ocean cyclone season is almost as long,
extending from April through December with peaks in May and again in November.
In the Southern Hemisphere, the cyclone season in the southern Indian and southwest
Pacific runs from late October through May with a peak about Feb. 1.
Q. How are hurricanes named?
A. Tropical storms in the Atlantic are named by the World Meteorological
Organization. There are six lists used in rotation. Consequently, the list used this year
will next be used in 2006. The lists are changed only if a storm is so infamous because of
loss of life or property that its name is retired and replaced.
Q. What will this year's hurricanes be named?
A. In the Atlantic the first named storm will be Alberto. It will be followed by Beryl,
Chris, Debby, Ernesto, Florence, Gordon,
Helene, Isaac, Joyce, Keith, Leslie, Michael, Nadine, Oscar, Patty, Rafael, Sandy, Tony,
Valerie and William.
In the Eastern Pacific the 2000 list is Aletta, Bud, Carlotta, Daniel, Emilia, Fabio,
Gilma, Hector, Ileana, John, Kristy, Lane, Miriam, Norman, Olivia, Paul, Rosa, Sergio,
Tara, Vicente, Willa, Xavier, Yolanda and Zeke.
You'll notice that none of the names starts with Q or U; there just aren't enough names
beginning with those letters to go around. And for some reason, names starting with X, Y
or Z are OK in the Pacific but not in the Atlantic.
Hurricanes were originally identified by their latitude and longitude. In 1953 the World
Meteorological Organization began giving them women's names, and in 1979 the system was
broadened to include men's names and to reflect Spanish and French influences.
Jan Null, founder of Golden Gate Weather Services and director of meteorology for
Planetweather.com, is a retired lead forecaster with the National Weather Service. Send
questions to Weather Corner, San Jose Mercury News, 750 Ridder Park Drive, San Jose,
Calif. 95190; phone (510) 657-2246, e-mail firstname.lastname@example.org or fax them to