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UPDATED: 9:00 am EDT, April 20, 2009
INLAND FLOODING A MAJOR ISSUE WITH TROPICAL CYCLONES
Most people think of wind and rain when visualizing what it must be like to experience a tropical storm or hurricane. What they don't often realize is how much rain actually falls and the potential that exists for extensive flooding problems. Tropical cyclones are by their very nature wet. The release of rain is actually part of the process that drives these storms. Condensation is a warming process and the excessive amounts of water that is stored in the tropical atmosphere is released in torrents of rain. For some areas that are in dire need of water, this heavy rain can be a welcome sight. However, too much of it can have very dangerous and often deadly consequences. It is all a matter of where and how long.
Typically, a slow moving tropical depression, tropical storm or hurricane will dump the most rainfall. This makes good sense for obvious reasons. However, even more swift moving systems can produce flooding rains if they encounter other forces in the atmosphere such as a cold front. In areas with mountains, such as the Greater Antilles and portions of Central America, the lifting effect, or orographic lift, can enhance rains from tropical cyclones causing massive mudslides and flash floods. This is especially true in Haiti and Honduras/Nicaragua where great losses of life have taken place over the last 20 years alone. For the United States, the problem is complex as a lot depends on where a tropical cyclone makes landfall, how fast it is moving and where it tracks after landfall.
Take TS Allison in 2001 as an example. The fairly disorganized storm made landfall near Galveston, TX in early June of that year. The slow moving storm dumped so much rain on the region that Houston was brought to a stand still for several days. The remnants of Allison continued to plague the northern Gulf Coast states for several days as it drifted around the region- slowly moving towards the Southeast and Mid-Atlantic states. Allison caused over 5 billion dollars in damage and killed nearly two dozen people. All of this from a mere tropical storm.
In 1969, category five hurricane Camille made history by wiping out a large portion of the Mississippi coast with an enormous storm surge. Camille had extremely high winds as well but it left its mark in the Appalachains of Virginia with flooding rains that people still talk about even today. Fast forward to 2004, hurricane Frances moved inland over Florida and then turned north in to the Southeast U.S. bringing flooding rains to the mountains of North Carolina. Before that event, the remnants of hurricane Gaston, just a few days prior, brought extreme flooding to portions of Richmond, Virginia. The list goes on and on and if we look just to last season, the big story with TS Fay was its rain. Melbourne, FL and surrounding areas set records from the amount of rain that came down. The slow moving storm dumped over 20 inches of rain in Brevard county and flooded some 15,000 homes across the state.
The biggest issue with inland flooding from tropical cyclones is deaths by drowning in vehicles. Too often, people try to cross rain-swollen road ways because they "know" the area or are in a hurry. It is said that only six inches of water can move a vehicle. This is especially true if the water is moving. Often times we see where swift moving water undermines the roadway, causing unseen holes, large enough to swallow cars and SUVs. Then, someone comes along and drives across dark, murky water only to be swept downstream, unable to escape. This is such a preventable tragedy and one that common sense can help to mitigate or even eliminate completely.
The best bet for preparing for the threat of excessive rain fall is to keep informed. You won't know that too much rain may fall in your area until the storm or hurricane is practically right on top of you. From there, it is a matter of where the rain falls and how much. Again, the use of common sense is the best plan of action. Don't let children play around flooded ditches or culverts. It may look fun but the water is full of toxins, animals and insects and can be swift-moving. Stay home, don't drive through flooded areas- no matter how well you know them or what vehicle you have. Moving water is your worst enemy- if it can carve out the Grand Canyon, it can sweep your huge SUV away with little warning. I have posted a link to the Southeast River Forecast Center as a resource this coming hurricane season- and any time of the year. Check out the site- it offers excellent data and information concerning the threat from freshwater flooding. We'll talk more about inland flooding from tropical cyclones on Wednesday night's edition of HurricaneTrack News/Talk.
Below is our Atlantic Basin tropical cyclone tracking map. When an active tropical cyclone exists, the map will be activated so that you may click on it and/or mouse over the symbols for more information. During periods of no activity, the map will serve to point out areas of interest that may develop. This information is based primarily on National Hurricane Center data but may reflect additional information based on computer model output. We do not make our own forecasts but will point out areas of potential development. All of the information will be compiled using either official information from the NHC or computer model data suggesting development beyond the 48 hour time period of the NHC Tropical Weather Outlook.
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