Hurricane Dorian

This satellite image taken Wednesday, Aug. 28, 2019, and provided by the National Oceanic and Atmospheric Administration shows Dorian, a Category 1 hurricane, crossing over the U.S. and British Virgin Islands.

Q: What are the leading threats from hurricanes?

A: In a hurricane, objects in the path of strong winds bear what is known as a wind load. This wind load is the product of the area of the object times the wind pressure (equal to 0.00256 x windspeed2) times a laboratory-determined drag coefficient. For a wall the drag has a value of 2 while for a telephone pole it is only 0.8.

A 10-foot by 20-foot wall subjected to 150 mph winds like those delivered by Atlantic Ocean hurricanes Irma and Maria in 2017 would feel a wind load of 8.7 tons.

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The most effective protection against structural damage to a house in the face of such winds is to shutter the windows. The primary reason to do so is to keep the strong winds outside of the dwelling. If a window breaks and the wind can come rushing in, a lot more damage can be done to the structure.

The storm surge associated with hurricanes results from the piling up of water ahead of the storm by its strong winds. It turns out that the depth of the storm surge is best predicted by the strength of the storm about 18 hours before it makes landfall. This is because any changes in the intensity of the winds in those last 18 hours have too little time to affect the mountain of water that has already been produced.

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"Weather Guys" Steve Ackerman and Jonathan Martin are professors in the University of Wisconsin-Madison department of atmospheric and oceanic sciences.


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