WEATHER CORNER

BY JAN NULL
Special to the Mercury News

All About Hurricanes

THIS week's Weather Corner focuses on hurricanes. These powerful
storms from the tropics are among nature's most deadly and damaging
phenomena.

Q What is a hurricane?

A The term ``hurricane'' refers to a strong tropical cyclone -- the generic term for a low-pressure system over tropical or sub-tropical waters with organized thunderstorm activity. Additionally, tropical storms have definite cyclonic (counterclockwise in the Northern Hemisphere and
clockwise in the Southern Hemisphere) surface winds around the center of the storms. 

These tropical storm systems are defined as a hurricane when their sustained wind speeds reach 74 mph. When the wind speeds are between 39 mph and 73 mph they are tropical storms. If the winds are less than 39 mph they are referred to as tropical disturbances.

The term hurricane is specific to the Atlantic and the central and eastern Pacific. The same type of weather systems in the western Pacific are called typhoons and in the Indian Ocean they are cyclones.

Hurricane is derived from the Mayan hurican, the Carib god of evil, who blew his breath across the chaotic water and brought forth dry land.

Q How are hurricanes ranked?

A A scale called Saffir-Simpson categorizes hurricane-force winds. This gives ratings from 1 to 5 based on the storm's wind speed. 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 in excess of 155 mph. 

Category 4 and 5 storms are far more deadly and devastating than lesser category storms, but they also are relatively rare. Since 1900 only 13 Category 4 storms and three Category 5 storms have made landfall in the United States.

Q What are the hazards associated with hurricanes? 

A Even though hurricanes are thought of as huge wind storms, most of their death and destruction is the result of flooding. This comes from the copious rainfall contained in the humid tropical air that feeds these storms, rainfall that can reach a foot or more daily.

Coastal areas also are susceptible to the ``storm surge,'' which can range from five feet in a Category 1 storm to greater than 18 feet with a Category 5. The storm surge is the piling up of water by the hurricane's winds as well as the rise in sea level due to the extremely low barometric
pressure associated with tropical storms. The surge causes the inundation of coastal areas that are often densely populated and difficult to evacuate.

Tornadoes are also a serious byproduct of hurricanes and tropical storms as they move inland. 

Q When is hurricane season?

A The hurricane season in the Atlantic, Caribbean and Gulf of Mexico, and the central Pacific, runs from June 1 to Nov. 30. In the eastern Pacific, hurricane season runs from May 15 to Nov. 30. 

Q How and why are hurricanes given names? 

A Hurricanes were originally identified by their latitude and longitude. This was cumbersome, especially when more than one storm was active at the same time. During World War II, tropical storms over the Pacific were informally given women's names by Army and Navy meteorologists.
In 1950 this practice was extended into the Atlantic with the military phonetic alphabet (i.e., Able-Baker-Charlie-etc.). In 1953 the U.S. Weather Bureau switched to women's names for the Atlantic and eastern Pacific storms. In 1979, the World Meteorological Organization and the
U.S. National Weather Service developed a list of alternating men's and women's names that reflected the influence of English, Spanish and French. The lists are recycled every six years, although the names of particularly disastrous storms, like Andrew or Hugo, are removed.

The names for the 1999 season in the Atlantic: Arlene, Bret, Cindy, Dennis, Emily, Floyd, Gert, Harvey, Irene, Jose, Katrina, Lenny, Maria, Nate, Ophelia, Philippe, Rita, Stan, Tammy, Vince, Wilma. 

The names for the 1999 season in the eastern Pacific: Adrian, Beatriz, Calvin, Dora, Eugene, Fernanda, Greg, Hillary, Irwin, Jova, Kenneth, Lidia, Max, Norma, Otis, Pilar, Ramon, Selma, Todd, Veronica, Wiley, Xina, York, Zelda.

Q Has California ever had a hurricane? 

A Fortunately, the waters along the California coast are too cold. Hurricanes derive much of their energy from the warm tropical waters they pass over, and it takes water temperatures of at least 80 degrees to sustain them. Readings along the Southern California coast are usually in
the 68- to 72 degree range.

While California has never felt the winds of a hurricane, it has often felt their indirect impact. As hurricanes in the eastern Pacific dissipate, their moisture may spread northward into California and result in thunderstorms, heavy rain and flooding. Hurricane Kathleen in September 1976 caused $65 million in damage to California's agriculture.

Q Will humans ever be able to control hurricanes?

A Some efforts were made in the 1970s to ``cloud seed'' hurricanes when they were still over the ocean in the hopes of dissipating some of their energy. The results were inconclusive at best, and no further experiments have been done.

A suggestion is sometimes made to explode a hydrogen bomb within a hurricane to blow it apart. Besides the fact it would result in radioactive rain, the force of such a bomb is insignificant in relation to a hurricane. A hurricane is made up of hundreds of thunderstorms, each of which
releases the energy of many atomic bombs.

Q Where can I find out more about hurricanes and tropical storms?

A Three of my favorite Web sites are the National Hurricane Center, http://www.nhc.noaa.gov, USA Today at http://www.usatoday.com/weather/whur0.htm and UIUC has an excellent
tutorial at http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/home.rxml

Jan Null, founder of Golden Gate Weather Services, 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. You also can telephone and fax them at (510) 657-2246 or e-mail them weathercorner@ggweather.com.