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Forecasting for devastation

A satellite image of Hurricane Katrina taken at 11:45 a.m. EDT, August 28, 2005, one day before it made landfall in Louisiana. On August 28, Katrina became a Category 5 storm, the most severe, but no one could guess the damage it would eventually cause. (Image: NOAA)

The recent Hurricane Isaac, as well as Hurricane Katrina in 2005, taught us that the amount of damage a hurricane inflicts doesn't necessarily coincide with the forecast intensity of the storm.  

Unlike tornadoes, whose very development is unpredictable and whose path even more so, hurricanes give many days' warning of their landfall, and many hours' warning as to their path of destruction. And yet that is still not enough to save lives and spare serious damage from occurring.

Hurricanes have been part of U.S. history since the beginning. Christopher Columbus encountered one in 1495 near Hispaniola. In the 1500s, hurricanes were responsible for sinking a French fleet off the coast of Florida as well as a Spanish expedition, save the one ship that made it through to found a colony near Pensacola.

The island of Bermuda was settled in 1609 when a ship carrying 150 men, women, and children who were bound for Jamestown took refuge from a hurricane on the island and stayed there. Even Benjamin Franklin observed a hurricane as it worked its way up the Atlantic coast in 1743.

In 1819, a Harvard professor first described a hurricane as a "moving vortex." As scientists began to have a better understanding of hurricanes, they were able to issue warnings before they reached landfall. Not surprisingly, however, they weren't very accurate. The first hurricane warning was issued in 1873 by the U.S. Army Signal Corps for a hurricane approaching New England. The hurricane never made landfall.

In the early 1900s, scientists began understanding the importance of storm surge and the resultant flooding. But even though scientists were beginning to forecast hurricanes, the deadliest hurricane in U.S. history hit with little warning at Galveston in 1900. The Category 4 storm killed between 6,000 and 12,000 people with most being killed in the storm surge, which ranged from 8 to 15 feet.

In 1943, an Air Force pilot was the first to fly a plane into the eye of a Category 1 hurricane. Future such missions would provide valuable forecasting information.

The first hurricane forecast models began to be developed in the 1950s, using dynamical and statistical models. Dynamical models measure atmospheric conditions such as temperature, barometric pressure, wind speed and direction, and moisture in the atmosphere at given locations and at different times. Using this data, predictions are made as to how wind speed and direction around the hurricane may change over time.

Statistical models look at information about a specific hurricane, such as location and time of year, and compare it to data of the behavior of past hurricanes in similar situations. They are used in conjunction with dynamical models.

In the 1960s, satellites were used to provide data for forecasting, aiding in its reliability, and extending advance warning to three days.  

In 1975, the Saffir-Simpson scale for measuring hurricane strength was created by meteorologists Herbert Saffir and Robert Simpson. It was a way to categorize the intensity of a hurricane on a scale of one to five based on the predicted amount of wind damage.

With improvements in forecasting, hurricanes continued to wreak devastation, but with less loss of life. In 1992, Hurricane Andrew caused over $26 billion in damage as it hit South Florida and then Louisiana, but it only resulted in 23 U.S. deaths.

However, when Hurricane Katrina hit Louisiana in 2005, the unexpected massive flooding caused when the levees failed led to over 1,800 deaths and $81 billion in property damage, three times more than Andrew. Hurricane Katrina, which had reached Category 5 status, was a Category 3 when it made landfall. However, the storm surge did damage all along the Gulf coast from central Florida to Texas, and many New Orleans residents stayed, having not been warned that the levees could fail. The catastrophic event caused flooding of up to 28 feet over normal levels.

When forecasters looked at the models for Hurricane Isaac, it was believed that the new levees built in New Orleans since Hurricane Katrina would hold, and they did. However, there have been complaints that the new levees pushed the water into smaller outlying communities, flooding them to the extent that one resident called it "worse than Katrina."

Meteorologists know that hurricane deaths result primarily from the storm surge, so they are now working on better prediction of the surge. The National Weather Service (NWS) monitors coastal flooding conditions 24 hours a day, 7 days a week, and issues watches and warnings, including Hurricane Local Statements. These provide details on a storm's impact on a specific localized area, because surge depends on the topography of the land just off the coastline, which may vary. In this way, the NWS tries to help localities that will be in the hardest-hit zones to better prepare for the damage and get people out of harm's way.

Hurricanes can't be avoided. But as each hurricane wreaks its own particular brand of havoc, meteorologists are learning more about how to better forecast not only the trajectory and strength of the hurricane, but the damage potential as well.  

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Representative Image Caption
A satellite image of Hurricane Katrina taken at 11:45 a.m. EDT, August 28, 2005, one day before it made landfall in Louisiana. On August 28, Katrina became a Category 5 storm, the most severe, but no one could guess the damage it would eventually cause. (Image: NOAA)
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