Operational Implementation of a Coupled Version of SLOSH and Coastal Wave Modeling at the National Hurricane Center: Current Applications and Future Plans

The National Hurricane Program (NHP) is a Federal Partnership Program between the Federal Emergency Management Agency (FEMA), the U.S. Army Corps of Engineers (USACE), and the National Oceanic and Atmospheric Administration (NOAA). The NHP is mandated by Federal Law to conduct Hurricane Evacuation Studies (HES) for the US Gulf of Mexico and Atlantic coastlines as well as Puerto Rico, the Virgin Islands, Guam, and portions of Hawaii in the Pacific Ocean. A HES consists of several related analyses (Hazards, Vulnerability, Shelter, Behavioral, and Transportation) that develop technical data concerning hurricane hazards, vulnerability of the population, public response to evacuation advisories, timing of evacuations, and sheltering needs for various hurricane threat situations. Their purpose is to provide emergency management officials with information that assists them in hurricane evacuation planning and decision making. One of the initial inputs required to conduct a HES is identification of the storm surge risk, namely identification of the areas most vulnerable to storm surge, within the HES area. NOAA, specifically the National Weather Service's (NWS) National Hurricane Center (NHC), utilizes the SLOSH hydrodynamic model to simulate storm surge, both its height and inland extent, under varying scenarios. This information is then provided to the NHP for application in the HES, planning and mitigation activities, shelter and transportation analysis, and overall risk analyses. Additionally, NOAA’s National Weather Service also utilizes the SLOSH modeling system for real-time predictions and warnings of coastal flooding. Historically, both HES and real-time predictions have been absent within areas where coastal wave breaking contributes significantly to the total water rise due to absence of wave radiation stresses in the SLOSH modeling system. While coupled hydrodynamic and wave models exists, the extreme computational cost and prohibitively long runtimes have thus far prevented the adoption of these systems within NOAA’s operational environment. More recently, NOAA has developed an efficient wave modeling system for coupling with SLOSH which overcomes these limitations and allows, for the first-time ever, the adoption of a coupled wave and surge modeling system for tropical cyclones. This paper will focus on the operational implementation of an advanced version of SLOSH, with waves, for the purposes of developing HES and real-time predictions within areas dominated by wave physics.