Using SDP
The SLOSH Display Program (SDP) is only one of several tools used by emergency management agencies to determine who is at risk and should evacuate. The exact location and timing of a hurricane’s landfall is crucial in determining which areas will be inundated by the storm surge. Small changes in track, intensity, size, forward speed, and landfall location can have huge impacts on storm surge. The forecast track and intensity of a tropical cyclone are subject to large errors, thus a single simulation (deterministic run) of the SLOSH model does not always provide an accurate depiction of the true storm surge vulnerability. NHC, therefore, employs an ensemble approach by using thousands of SLOSH simulations for each geographic area. These ensemble simulations accurately account for the full spectrum of storm characteristics by including different:
- Directions of motion
- Landfall locations
- Intensities
- Storm sizes
- Forward speeds
The results of these simulations are composited (grouped) into storm surge atlases or maps. Available SLOSH ensemble products include the MEOW, MOM, and probabilistic storm surge products:
- The MEOW (Maximum Envelope of Water) provides an estimate of the potential inundation from a hurricane of a given category moving in a given direction at a given forward speed. MEOWs are pre-computed products available anytime. The MEOW plans for the worst case scenario. (Note: MEOW also refers to Maximum Envelope of Winds, which is a different hurricane product produced by the Inland Wind Model.)
Example MEOW graphic for all hypothetical Category 2 storms that move in a northwest direction through the New Orleans Basin at a forward speed of 15 mph. This MEOW is closest to the characteristics of Hurricane Gustav (2008), which made it a useful decision-making tool prior to that storm making landfall.
- MOM (Maximum of Maximums or Maximum of MEOW) displays a composite of the maximum storm surge height for all hurricanes of a given strength/intensity (i.e. Category, 1, 2, 3, 4, and 5 on the Saffir–Simpson Hurricane Wind Scale). There are only 5 MOMs per geographical region, one per Saffir–Simpson Hurricane Wind Scale category. MOMs are pre-computed products available anytime.
Example MOM graphic showing the maximum storm surge height for all hypothetical Category 2 storms for this region. Unlike the MEOW, it includes all forward speeds and directions.
- Probabilistic Storm Surge product (P-Surge) is produced whenever a hurricane watch or warning is in effect for any portion of the United States coastline. It is the result of multiple SLOSH simulations based on perturbations (alternate scenarios) of the operational NHC track, intensity, and size forecast. The perturbations used are based on the performance (accuracy) of previous year’s forecasts. P-Surge is available with other routine products on the NHC website.
Example of P-Surge graphic for Hurricane Gustav (2008), 24 hours before landfall