Tip Sheet: Hurricanes

BOULDER -- This year may bring a bumper crop of Atlantic hurricanes, thanks to the influence of La Nina and other factors. Below is a range of Web sites, answers to frequently asked questions, and a set of hurricane experts from the National Center for Atmospheric Research (NCAR) and from member institutions of the University Corporation for Atmospheric Research (UCAR). NCAR's primary sponsor is the National Science Foundation. NCAR is managed by UCAR, a consortium of more than 60 universities offering Ph.D.s in atmospheric and related sciences.

Hurricane experts

Roger Pielke, Jr., 303-497-8111, rogerp@ucar.edu
NCAR Environmental and Societal Impacts Group

Specialty: Hurricane impacts and related societal factors. A political scientist, Pielke has completed in-depth studies of the societal vulnerability to hurricanes of the U.S. Gulf and Atlantic coasts. In the October 1999 issue of the Bulletin of the American Meteorological Society, Pielke and colleague Christopher Landsea (see listing below) will outline the relationship of El Niño and La Niña to U.S. hurricane damage. They note that most La Niña years (17 out of 22)--but only a few El Niño years (7 out of 22)--produce a U.S. landfall causing at least $1 billion in damage. Catastrophic storms of $10 billion or more are so rare that their relationships to El Niño or La Niña are difficult to assess. The study is on line. Pielke and Landsea have also examined trends in population and wealth to calculate the costs of historic U.S. hurricanes in 1997 dollars. Pielke is the co-author of Hurricanes: Their Nature and Impacts on Society (Wiley, 1997) and creator of the Extreme Weather Sourcebook (see Web sites below).

Robert Gall, 303-497-8160, gall@ucar.edu
NCAR Mesoscale and Microscale Meteorology Division/U.S. Weather Research Program

Specialty: Analysis of tropical systems. Through radar analysis, Gall has uncovered fine-scale bands that spiral around the centers of hurricanes. These bands could be related to small- scale wind peaks that cause some of a hurricane's worst damage. Gall and fellow NCAR scientist John Tuttle have also developed a technique that uses radar data to estimate surface winds at points that lie beyond the typical range of Doppler radar. Gall is now serving a two-year term as lead scientist of the U.S. Weather Research Program, a multiagency project to examine high-impact phenomena, including hurricane landfall.

Terry Hock, 303-497-8767, hock@ucar.edu
NCAR Atmospheric Technology Division

Specialty: Measurement of winds through Global Positioning System (GPS) dropsondes. Hock led NCAR's development of the revolutionary GPS device. The dropsondes have been deployed over the past three years from hurricane-hunting aircraft. They report winds between flight level and the sea surface at 16-foot (5-meter) intervals, a precision about 100 times greater than before. The new dropsondes have gathered the first-ever wind data at high resolution from the eyewall that swirls around the calm eye of a hurricane.

Christopher Landsea, 305-361-4357, landsea@aoml.noaa.gov
NOAA Hurricane Research Division

Specialty: Seasonal hurricane forecasting and hurricane climatology. Landsea is a collaborator with hurricane forecaster William Gray (Colorado State University). He has studied patterns of hurricane occurrence and damage along the Gulf and Atlantic coasts over the past century and is the author of a frequently- asked-questions document on the World Wide Web (see below).

Jay Baker, 850-893-8993, jbaker@coss.fsu.edu
Florida State University, Department of Geography

Specialty: Human response to hurricanes, including evacuations. Through on-site visits and interviews after hurricanes, Baker has examined how people respond to warnings and evacuation orders. He also has studied how emergency managers use forecasts and other information to implement evacuation plans.

Related sites on the World Wide Web

NOAA Tropical Prediction Center (TPC)

This site includes official outlooks, climatology, and statistics on hurricanes, tropical storms, and tropical depressions. TPC includes the National Hurricane Center, which issues hurricane watches and warnings and calculates official projections of storm tracks.

NCAR/ESIG Extreme Weather Sourcebook

This site offers yearly totals and state-by-state comparisons for hurricane damages between 1925 and 1995. The figures are normalized to account for trends in population and wealth. Florida, Texas, and Louisiana are the leaders for hurricane damage, with Florida averaging over $2 billion per year.

CSU Tropical Meteorology Project

This site, from Colorado State University, includes
• the latest long-range hurricane outlooks from CSU professor William Gray

• a comprehensive set of answers to frequently asked questions about hurricanes and other tropical cyclones, compiled by Chris Landsea.

This site includes a wealth of links to Web-based hurricane information. Because popular Web sites often become busy and difficult to access when a major hurricane approaches, the author includes several alternate addresses for frequently sought items, such as the latest storm intensities and projected tracks.

Background information on hurricanes

What is a hurricane? Each year a number of tropical disturbances--centers of low pressure--move westward across the Atlantic, Pacific, and Indian Oceans. Some of these become depressions--more organized disturbances with sustained surface winds of up to 38 miles per hour (61 kilometers per hour). Should the winds become stronger, the system becomes a tropical storm and is given a name. If the winds reach 74 mph (119 km/hr), the storm is reclassified as a hurricane (other names, such as typhoon, are used outside of the Atlantic). Eventually, most of these systems either strike land and quickly weaken or recurve over the ocean, moving north and east as they become caught up in the midlatitude westerly winds and lose their tropical characteristics.

What's the difference between a hurricane and a tornado? Tornadoes are spawned by thunderstorms, while hurricanes are made up of many showers and thunderstorms (which can themselves spawn tornadoes upon landfall). Hurricanes gather energy from the warmth of the ocean. A hurricane's eye is typically 10 to 15 miles (16 to 24 km) wide, and winds around it are as strong as 150 to 200 mph (240 to 320 km/hr). The hurricane circulation can be hundreds of miles across. Even the largest tornadoes are only about a mile across, although their winds can reach 300 mph (480 km/hr). Tropical storms can survive for weeks, while most tornadoes exist for much less than an hour.

How many tropical systems occur on average each year? Globally, an average of around 85 tropical storms and 45 hurricanes/typhoons form per year. The tropical Atlantic and Gulf of Mexico--the sources of U.S. hurricanes--produce an average of nine named storms per year, with around six of those becoming hurricanes and two of those becoming intense hurricanes (ones with sustained surface winds exceeding 110 mph, or 177 km/hr). The period since 1995 has been unusually active. Even though 1997 saw few Atlantic storms, the 1995-1998 total was the largest on record for a four-year span in the Atlantic, with 53 named storms, including 32 hurricanes.

How are hurricanes predicted? Some climate factors are known to affect hurricane frequency for a given ocean or a given year. For instance, El Niño enhances upper-level winds that tend to suppress Atlantic hurricanes, while La Niña has the opposite effect. Each year, out of dozens of disturbances that cross the tropical Atlantic, only a handful encounter the right combination of light wind shear and warm ocean temperatures that allows for hurricane development. The behavior of tropical storms and hurricanes is predicted by high-resolution computer models at the NOAA Tropical Prediction Center, the federal agency that issues hurricane watches and warnings (see Web site above). Hurricane motion can be projected with some skill out to five days. Changes in storm intensity are still difficult to predict, even within a day or two, but some progress has been made with better computer models. New observing tools, such as GPS dropsondes (see Terry Hock, above) and satellite-based radars that can sense unusually deep layers of warm water, are also helping to improve forecasts by providing a better picture of current conditions.

What are the storm names for this year and upcoming years? Since 1953, Atlantic tropical storms have been named from lists originated by the National Hurricane Center and now maintained and updated by Region 4 of the World Meteorological Organization. The lists featured only women's names until 1979. Six lists are used in rotation. The names of the most severe hurricanes, such as 1998's Mitch, are retired permanently. Below are the lists for 1999-2004.

Atlantic basin hurricane names

1999	2000	2001	2002	2003	2004
Arlene	Alberto	Allison	Arthur	Ana	Alex
Bret	Beryl	Barry	Bertha	Bill	Bonnie
Cindy	Chris	Chantal	Cesar	Claudette	Charley
Dennis	Debby	Dean	Dolly	Danny	Danielle
Emily	Ernesto	Erin	Edouard	Erika	Earl
Floyd	Florence	Felix	Fran	Fabian	Frances
Gert	Gordon	Gabrielle	Gustav	Grace	Gaston
Harvey	Helene	Humberto	Hortense	Henri	Hermine
Irene	Isaac	Iris	Isidore	Isabel	Ivan
Jose	Joyce	Jerry	Josephine	Juan	Jeanne
Katrina	Keith	Karen	Kyle	Kate	Karl
Lenny	Leslie	Lorenzo	Lili	Larry	Lisa
Maria	Michael	Michelle	Marco	Mindy	Matthew
Nate	Nadine	Noel	Nana	Nicholas	Nicole
Ophelia	Oscar	Olga	Omar	Odette	Otto
Philippe	Patty	Pablo	Paloma	Peter	Paula
Rita	Rafael	Rebekah	Rene	Rose	Richard
Stan	Sandy	Sebastien	Sally	Sam	Shary
Tammy	Tony	Tanya	Teddy	Teresa	Tomas
Vince	Valerie	Van	Vicky	Victor	Virginie
Wilma	William	Wendy	Wilfred	Wanda	Walter