New Tool to Keep You Ahead of the Storm

Weather Talk
Friday, May 27, 2011 - 2:21pm

When it comes to hurricanes, most people believe that the strong winds that come along with it will produce the most damage. However, it is usually the storm surge, the wall of water produce by a hurricane, which does the most harm. In recent years, most hurricane forecasters used satellite imagery and dropsondes (the collector of current storm data) to predict the storm’s path and intensity. Now forecasters have a new tool in the belt, they have high resolution modeling. Modeling has become a very integral part in providing better accuracy of strength, intensity, and landfall of hurricanes. Improvements have also been made on the predictability of the incoming hurricane and its storm surge. Researchers at Louisiana State University and the National Weather Service have teamed up to create a computerized numerical model that estimates the storm surge heights by using historical, hypothetical, or predicted hurricanes. It takes in account a melting pot of atmospheric variables from hurricane pressure, size, forward speed, winds, and track data. The genius model also takes into account the unique features of the coastline that make one place different from another. In other words, the model is able to differentiate between the marsh-like shoreline of Louisiana versus the sandy shoreline of the Florida Panhandle by being feed the parameters that are specific location. The model understands and recognizes jagged bay and river basins, water depths, bridges, roads, levees, and other physical features. This state of the art model is fittingly called SLOSH. SLOSH is an acronym for Sea, Lake, and Overland Surges from Hurricanes. The SLOSH model has been used in recent years and proved to be a valuable asset in the proper evaluation for a hurricane evacuation.
Ahead of a hurricane, decision making in a timely manner is very invaluable. Since every second counts, it is important that emergency and government officials make the decision quickly. To make better evaluations, quick and accurate information is needed. However, at the time the decision is made, the error in the hurricane's track and intensity may be large. So to aid emergency managers in planning for hurricanes, the potential surge for an area is computed. This is done by running SLOSH with hypothetical hurricanes with various landfall directions and locations, Saffir-Simpson categories, forward speeds, sizes, and tide levels. Each individual run generates an example of a possible hurricane storm surge. Therefore, when planning an evacuation, government officials, first responders, and emergency management know how to plan accordingly. They can use current hurricane information and compare it with past storms to find the best answer. The best answer may save millions of people from packing up their belongings and leaving town. It also saves millions of dollars in evacuation costs.
As of recent, the SLOSH model has been applied to and encompasses the entire U.S. coastline from northern Maine to southern Texas. In addition, the coverage extends to Hawaii, Guam, Puerto Rico, and the U.S. Virgin Islands. By covering the entire coastline, it becomes much easier to prepare for any storm track and its intensity.
The best part about the computerized model is its proficiency. The Storm Surge Unit, a department of the National Weather Service, says “The SLOSH model is computationally efficient; resulting in fast computer runs which makes it an ideal operational system. It is able to resolve flow through barriers, gaps, and passes and models deep passes between bodies of water. It also resolves inland inundation and the overtopping of barrier systems, levees, and roads.” The SLOSH model is also accurate to within +/- 20 percent which is extremely rare in long range modeling. To put that accuracy into perspective, the model calculates a peak 10 foot storm surge for the event; you can expect the observed peak to range from 8 to 12 feet. When understanding the power of a storm surge, a few feet of water can make a huge difference. A foot of water can sweep away a car, while a few feet of water can sweep away a house.
However, the model does have a few limitations. The Storm Surge Unit notes “The SLOSH model does not explicitly model the impacts of waves on top of the surge, it does not account for normal river flow or rain flooding, nor does it explicitly model the astronomical tide.” In addition, the point of a hurricane's landfall is crucial to determining which areas will be inundated by the storm surge. When the hurricane forecast track is inaccurate, the SLOSH model results will be inaccurate. The SLOSH model, therefore, is best used for defining the potential maximum surge for a location. Good news, future advancements for the SLOSH model already in progress will patch up some of these limitations.
As we all know, preparation is the best policy. You can never be over prepared. The SLOSH model helps to slim error estimates and gives a high resolution snap shot of possible flooding dangers. It has become a great tool in the fight for hurricane safety.

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