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Hurricane Irene sends reminder to prepare for possible tornadoes

By Staff | Aug 22, 2011

All eyes are on Hurricane Irene, and concerns about where that storm makes landfall may divert attention from other winds that blow as hurricanes approach. Hurricanes spawn tornadoes, and data seems to show that the tendency toward tornadoes has increased. According to the Insurance Information Institute (I.I.I.), tornadoes could form thousands of miles away from where a tropical storm hits.

Hurricanes and tropical storms produce tornadoes because thunderstorms are embedded in rain bands that are far from the center of the hurricane, although tornadoes can also occur near the eyewall. Usually, tornadoes produced by a hurricane are relatively weak and short-lived, but they can still pose a threat. Almost all tropical cyclones making landfall in the U.S. spawn at least one tornado, according to the National Weather Service, and some spawn dozens of them.

The largest known outbreak of tropical cyclone tornadoes was caused by Hurricane Ivan in 2004, with 127 tornadoes forming over a three-day period, according to data collected by The Tornado Project of the Universities Space Research Association. Eighteen of those tornadoes impacted Florida, and Ivan-caused tornadoes struck areas as far north as Virginia, Maryland and Pennsylvania.

A storm does not have to reach hurricane strength to raise the tornado threat. Tropical Storm Fay in 2008 was responsible for at least 49 tornadoes as it traversed Florida and other Southern states, three of which were rated with winds as powerful as a Category 3 hurricane.

While a tropical storm often weakens when it makes landfall as winds near the surface slow down, winds near the top maintain their momentum. This is what leads to tornadoes. Because Gulf coast states are more fully exposed to the right-front quadrant of a tropical cyclone when it hits land, they are more likely to experience tornadoes than the Atlantic coast. “Winds from tornadoes can far exceed the strength of hurricane-force winds, but hurricanes cause more damage due to their size and duration,” said Lynne McChristian, Florida representative for the I.I.I. “Tornadoes last for minutes and are small in diameter, while hurricanes can last for hours and stretch across many miles, bringing rain that leads to flooding.”

Source: Insurance Information Institute