Colorado State’s William Gray Launches Web Site that Features Hurricane Landfall Probabilities for 205 U.S. Coastal Counties

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A new Web tool is providing probabilities of tropical storm-force, hurricane-force and intense hurricane-force winds making landfall in specific locations along the U.S. East and Gulf Coasts within a variety of time periods, including this year and over the next 50 years. William Gray and Philip Klotzbach of the Colorado State University hurricane forecast team, with assistance from the GeoGraphics Laboratory at Bridgewater State College in Massachusetts, today officially launched the United States Landfall Probability Web site.

In addition to providing the odds of a direct hit, the site also gives the probabilities of tropical cyclones impacting an area, such as when citizens take precautionary actions in response to a hurricane watch or warning issued for a larger region.

Probabilities are available for 11 regions, 55 sub-regions and 205 individual counties along the U.S. coastline from Brownsville, Texas, to Eastport, Maine. The Web site, available to the public at, is the first accessible Internet tool that adjusts landfall probabilities for regions, sub-regions and counties based on the current climate and its projected effects on the upcoming hurricane season. The probabilities will adjust with changing ocean and atmospheric conditions.

"Although we have traditionally provided hurricane landfall probabilities for large coastal regions, most individuals who live along the coastline are unaware of the statistical chances of a hurricane striking their specific area. Based on years of feedback, it has been made clear that this is the information most people really want," said William Gray, professor of atmospheric science at Colorado State. "Therefore, we have created the Landfall Probability Web site to provide this information and arm individuals with data they can use to help them make important decisions regarding home building, hurricane insurance and other areas of their daily lives."

The probability of an intense hurricane making landfall in any one given year may seem low. However, the probability of a named storm making landfall grows considerably as the number of years increase. For example, the probability of hurricane-force winds in any one year in Miami-Dade County is 2.5 percent, but for 50 years the probability increases to 58 percent. Gray and Klotzbach feel it is these longer time period probabilities that will be most informative and helpful.

"Fifty-year probabilities of landfalling storms have been included in this study because most structures are built to last a minimum of 50 years, and construction decisions on the cost of building design and materials that protect against hurricanes should be based on the longer-range period," said Klotzbach. "If a county has a relatively large likelihood of a hurricane making landfall over a 50-year period, people would probably want to construct buildings to withstand at least minimal hurricane-force winds and/or purchase hurricane insurance. If, on the other hand, the 50-year probability is very low, individuals may choose not to spend the extra money for hurricane-force resistant buildings. Either way, this site will provide data to help coastal residents make informed decisions."

In addition to landfall probabilities, the site also includes estimated probabilities of being in the vicinity of tropical cyclone-force winds. Calculations have been made for the potential of tropical storm-force, hurricane-force and intense hurricane-force winds that influence all coastal counties from Texas to Maine. These values take into account the inherent uncertainty in tropical cyclone track and intensity forecasting.

For example, when a hurricane is located in the Gulf of Mexico, many residents along the entire Gulf begin to take preliminary action to protect life and property.

Also, hurricane watches often are issued for a much larger area than the area that will go under warning or will actually experience high winds of these velocities. The resulting estimated probability of being influenced by tropical storm-force or hurricane-force winds for any specific area is roughly 4 times to 9 times the yearly probability of being hit directly by a hurricane.

Probabilities are different than forecasts in that probabilities are mathematical calculations based on – in this case – 100 years of past tropical cyclone landfall information (1900-1999). Unlike forecasts, probabilities do not predict how many landfalling hurricanes will occur in a specific year, but rather provide the mathematical odds of a landfalling hurricane occurring in a year or other specified time period. Gray and Klotzbach continue to make their regular seasonal Atlantic basin hurricane forecasts.

Gray added that the Web site is in no way meant to decrease the public’s concern regarding the potential of landfalling hurricanes. In fact, he states that the site is meant, in part, to do the opposite – make people think about landfalling hurricanes in a way they can relate to, making the possibilities relevant to everyday lives. Gray maintains his longtime warning that the United States has been very lucky over the past few decades in witnessing very few major hurricanes making landfall in Florida and along the East Coast, but that climatology will eventually right itself and a great increase in landfalling hurricanes must be expected.

"We don’t know exactly when or where along the coast it will happen, but with the large coastal population growth in recent decades, it is inevitable that we will see hurricane-spawned destruction in coming years on a scale many, many times greater than what we have seen in the past," Gray said. "Coastal residents need to stay alert, and we hope this new Web site will aid in making decisions about hurricane preparations."

The landfall probability calculations were created based on the frequency of all U.S. landfalling tropical cyclones during the 20th century. Web users also can obtain landfall probability data for each large region, sub-region or county.

The 100-year data set also will be used to project potential cyclone damage values by region, sub-regions and counties within the coming months. Probabilities for daily to monthly tropical cyclone landfall also will be forthcoming within the year.

"This Web-based tool allows coastal residents to learn of the number and probabilities of tropical cyclone landfalls for their own local region," Klotzbach said. "This information should be valuable for coastal residents, emergency managers, local governments, insurance companies, business groups and others."