5.2 Quantifying Dynamic Storm Surge Forecasts for Emergency Management Decision Makers during Hurricane Irma

Tuesday, 9 January 2018: 10:45 AM
Ballroom D (ACC) (Austin, Texas)
Katherine Ertell, FEMA, Atlanta, GA; and B. Bolinski and R. Moulton

Quantifying Dynamic Storm Surge Forecasts for Emergency Management Decision Makers during Hurricane Irma

Emergency managers at all levels face the task of preparing for a multitude of hazards their respective communities may experience with a land-falling hurricane. There are many “tried and true" methods to plan for the eventuality of a Hurricane making landfall in the United States. One of the first steps of preparation is understanding and planning for the four main hazards (Storm Surge, Wind, Flooding, Tornadoes) specifically for the localized infrastructure, vulnerability, and risk in their community. The most variable, and potentially deadly, of these is Storm Surge. It is well known, and observed, that vulnerability to this hazard is extremely high in some communities. Unfortunately, Storm Surge also has the potential for the greatest loss of life and property. For these reasons, Storm Surge is one of the major planning factors for many emergency managers.

One of the better known methods for understanding the vulnerability of a community to storm surge is NOAA’s SLOSH model. Through this model thousands of community specific hurricane scenarios, a Maximum of Maximums (MOM), have been set for all hurricane intensities (TS-Cat 5). This is used as the basis or starting point for assessing a community’s vulnerability and exposure to storm surge from hurricanes. Once there is a hurricane, and a forecast track is issued with more confidence, we can leverage the uncertainty in possible tracks to further break down this “maximum” into similar landfall directions, forward speeds and tidal levels to create a catalog of Maximum Envelope of Water (MEOW). These MEOWs can help narrow down the extent of flooding based more on a specific threat—but every storm is inherently different.

When a hurricane threat is imminent and confidence increases in the forecast, the National Hurricane Center (NHC) issues products for storms surge based on the specific storm characteristics. The corresponding product is an exceedance potential (10%) that is based on a probabilistic scheme. This product is issued with every new forecast cycle for areas in a Storm Surge Watch/Warning, so as the forecast changes and as the storm gets closer (higher confidence) the surge exceedance changes.

Given these powerful storm surge products, Emergency Managers now have great data at their disposal to do an analysis of their community’s vulnerability. Using Geospatial Information Science (GIS), FEMA Region IV was able to not only assess a community’s risk to storm surge, but also provide leadership with the critical numbers they needed to make decisions about important pre landfall declarations to aid the State’s at risk with their response efforts. They key is when to use the right data, at the right time, for the correct decision making. This process ensures that the analysis is actually providing Emergency Managers with a clearer picture of what their community faces and is a crucial component to decisions when a hurricane is threatening.

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