UCAR Tip Sheet: Hurricanes

BOULDER -- This year is expected to bring another season of at- or above-average Atlantic hurricane activity, following the busiest six years on record. Here is a list of hurricane experts, hurricane- related Web sites, and answers to frequently asked questions. The experts are drawn from the National Center for Atmospheric Research (NCAR) and from member institutions of the University Corporation for Atmospheric Research (UCAR). NCAR, whose primary sponsor is the National Science Foundation, is managed by UCAR, a consortium of 66 universities offering Ph.D.s in atmospheric and related sciences.

Hurricane experts

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

Specialty: Analysis of tropical systems, including the wind structure in and near hurricane rainbands and the analysis of hurricane winds through radar-based techniques. Gall is also lead scientist of the U.S. Weather Research Program, a multiagency project to examine high-impact weather phenomena and improve forecasting. A USWRP-sponsored symposium on hurricane landfall was held this spring, and a major field program, CAMEX-4 (see Web page below), will take place in August and September.

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 this revolutionary device. The GPS dropsondes have been deployed over the past five years from hurricane-hunting aircraft. They report winds between flight level and the sea surface at 16-foot intervals, a precision about 100 times greater than before. The dropsondes have gathered the first-ever wind data at high resolution from the eyewall that swirls around the calm eye of a hurricane.

Chris Davis, 303-497-8990, cdavis@ucar.edu
NCAR Mesocale and Microscale Meteorology Division

Specialty: Evolution of hurricanes and other intense cyclones. Davis and colleagues have used the NCAR/Penn State Mesoscale Model, version 5 (MM5) to reproduce the fine-scale structure that drives the birth and strengthening of tropical cyclones. Davis has also studied the rapid intensification of nontropical coastal storms and the effects of mountains on midlatitude storm systems.

Roger Pielke, Jr., 303-735-3940, pielke@cires.colorado.edu
University of Colorado, Center for Science and Technology Policy Research

Specialty: Hurricane impacts and related societal factors. A political scientist, Pielke has written extensively on weather prediction and societal vulnerability, including the hurricane problem along the U.S. Gulf and Atlantic coasts. He and colleague Christopher Landsea (see below) have outlined the relationship of El Niño and La Niña to U.S. hurricane damage and examined trends in population and wealth to reevaluate the costs of historic U.S. hurricanes. Pielke is the co- author of Hurricanes: Their Nature and Impacts on Society (Wiley, 1997) and Prediction: Decision-Making and the Future of Nature (Island Press, 2000). He is also the creator of the Extreme Weather Sourcebook (see Web site below).

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

Specialty: Seasonal hurricane forecasting and hurricane climatology. Landsea, a collaborator with hurricane forecaster William Gray (Colorado State University), has studied patterns of hurricane occurrence and damage along the Gulf and Atlantic coasts over the past century. He is currently involved with the Atlantic Hurricane Reanalysis Project, a three-year effort to update and improve the National Hurricane Center's historical record of Atlantic tropical cyclones dating back to 1851.

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, including their use of information sources and perceptions of vulnerability to hurricane damage. He also has studied how emergency managers use forecasts and other information to implement evacuation plans.

Related sites on the World Wide Web

NCAR/ESIG Extreme Weather Sourcebook
This site offers yearly totals and state-by-state comparisons for hurricane damages between 1900 and 1999, normalized to account for trends in population and wealth. Florida, Texas, and North Carolina are the leaders for hurricane damage, with Florida averaging over $2 billion per year.

CAMEX-4
The Fourth Convection and Moisture EXperiment (CAMEX-4) will use NASA- funded aircraft and surface-based remote sensors to study the development, tracking, intensification, and landfalling impacts of tropical storms and hurricanes. The project will operate from August 16 to September 24 out of Jacksonville Naval Air Station, Florida.

CSU Tropical Meteorology Project
This site, from Colorado State University, includes seasonal hurricane outlooks from CSU professor William Gray and colleagues and a comprehensive set of answers to frequently asked questions about hurricanes and other tropical cyclones, compiled by Chris Landsea.

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.

NOAA Hurricane Research Division (HRD)
This site includes frequently asked questions about hurricanes and extensive background on the hurricane research conducted by HRD and collaborators, both national and international. A catalog of the hurricane-hunting flights conducted by HRD since 1994 is also included.

Hurricane FAQ

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. Should the winds become stronger, the system becomes a tropical storm and is given a name. If the winds reach 74 mph, 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 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 wide, and winds around it are as strong as 150 to 200 mph. 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. Tropical storms can survive for weeks, while most tornadoes exist for much less than an hour. There is no relationship between the size and intensity of a hurricane: some small hurricanes are very intense, such as Andrew in 1992, and some large ones can be relatively weak.

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 9 named storms per year, with around 6 of those becoming hurricanes and 2 of those becoming major hurricanes (ones with sustained surface winds exceeding 110 mph). The period since 1995 has been unusually active. Despite El Niño-linked reductions in hurricane activity during 1997, the years from 1995 to 2000 have been the most active six-year period on record. This includes the total number of named storms (79), hurricanes (49), and major hurricanes (23). However, only 3 of the 23 major hurricanes that developed in the Atlantic basin during this period reached the U.S. coastline (Opal, 1995; Fran, 1996; and Bret, 1999). Over the last century as a whole, a much higher fraction of major Atlantic hurricanes (73 out of 218) made landfall in the United States.

Which hurricanes have produced the worst U.S. damage in the last several years? Some of the greatest hurricane damage can occur from flooding after landfall, when the winds typically weaken but heavy rainfall may continue. In 1999, Hurricane Floyd's approach triggered the largest peacetime evacuation in U.S. history, but its worst impacts occurred well after landfall, particularly in North Carolina. Primarily through flooding, Floyd killed millions of animals and over 77 people, the largest human death toll related to a U.S. hurricane since 1972. In June 2001, the remnants of Hurricane Allison resulted in the most extensive flooding ever associated with a U.S. tropical storm. In the Houston metropolitan area, where more than 30 inches of rain were reported at several locations, damage estimates for Allison are near $2 billion, and at least 22 fatalities occurred.

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 (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. An upgraded atmosphere-ocean model introduced in 2001 by the NOAA Geophysical Fluid Dynamics Laboratory reduces the average error in hurricane intensity predictions by more than 25%. New observing tools, such as GPS dropsondes (see above) and satellite-based radars that can sense unusually deep layers of warm water, are helping to improve forecasts by better capturing current conditions.

What are the storm names for this year and beyond? Atlantic tropical cyclones are named from lists maintained by the World Meteorological Organization. The list of Atlantic names is available on the Web.