Hurricane Preparedness Blog

As a hurricane approaches, high winds can bring massive destruction, but it is a hurricane’s flooding that can cause the most damage…  A hurricane’s category (Category 1, Category 2, etc.)  tells the wind speed of a storm, but not other important factors, like how quickly the storm itself is moving, or the amount of rainfall a cyclone can produce.   But often, the aspect that can make a hurricane so destructive is how much rain it dumps on an area. The heavy rain that is common of tropical cyclones can produce heavy flooding, which is where both human life and property damage are greatly impacted. Several studies highlight this point:  since 1970, freshwater flooding was responsible for fifty-nine percent of all deaths caused by tropical cyclones in the United States, more than wind, surf, offshore flooding, and tornadoes combined.  Also, a U.S. Geological Survey conducted in 2000 found that during the 20th century in the U.S., floods were the number one natural disaster in terms of lives lost and property damage. There are several factors of a tropical cyclone that can contribute to inland flooding:

1.  Forward speed- Slowly moving tropical cylcones allow heavy rain to persist over a location.   We’ve just recently seen this happen with Hurricane Dolly.   Although her wind speed is relatively low compared to other hurricanes, she still is packing  a pretty heavy punch because she is so slow moving.   The slower she moves, the more rain is concentrated in one region.   As a result, many areas of southern Texas are being affected by flooding.
2. Orography-  As a tropical cyclone’s warm, moist, tropical air is forced up hills and mountains, rain is intensified.
3. Intersections with other weather features- When a tropical cyclone encounters another storm,  major rainfall is likely, and therefore major flooding is possible.
4. Antecedent conditions- If soil is already saturated, and water levels are already high in lakes, ponds, rivers, streams, and reservoirs, the chances of flooding are increased.

If you suspect flooding in your region, hydrological forecasts can be found at www.weather.gov.    For extensive information concerning floods, visit  OneStorm’s Flood Center. Sources Used:“Tropical Cyclone Flooding: A Deadly Inland Danger.”  NOAA.  March 2005.  23 July 2008.