The SLOSH Storm Surge data is compiled by the National Weather Service to assist emergency management officials determine the risk of hurricane related storm surge flooding in their area.  It is analyzed and created by "slosh basin" and takes into consideration the coastal bathometry as well as the effects of water being funneled into certain areas of the coastline.  

The SLOSH analysis has been done for the most of the US Coastline, Puerto Rico and the US Virgin Islands.  There are 2 types of analysis related to SLOSH.

MEOW - (Maximum Envelope of Water) and MOM (Maximum of Maximum).

The SLOSH Storm Surge, MEOWS and MOM's are calculated by the NWS as follows...

For each slosh basin:

1. Select hypothetical storms appropriate to those found from historical record: storm directions, forward speeds, (Saffir-Simpson) intensities, sizes (radius of maximum winds, or RMW), and landfall sites sufficiently close together (typically 15 miles or less) to adequately map the surge flood plain.

2. Generate the set of hypothetical storms. Typically there will be about 10 directions, 4 forward speeds, 5 intensities and 10 to 20 landfall points*, resulting in 2000 to 4000 individual storms.

*Because the average error of forecast position of eye landfall is about +/- 100 miles in 24 hours, no single storm is sufficient to map the potential for storm surge flooding in a basin in advance of storm landfall, as the likelihood of having chosen exactly the correct track is dangerously too small.. Instead, the SLOSH model is run with a family of storms. In the family, all storms share the same intensity, size, speed and direction. For example, the storm surge flood plain of a basin by Cat 3 hurricanes, heading northwest at 15 mph will be calculated by running SLOSH with a succession of NW15C3 storms that have landfall sites separated by 5 or 10 or 15 miles from those flanking it. Then, after all the storms in a family have been run, the maximum surge value at each grid square in the basin, from any storm in that family, is retained. The result is a Maximum Envelope Of Water, (or MEOW), for the NW15mph Category 3 storms, in the above example.

3. Create MEOW maps of SLOSH modeled storm surge, for each combination of storm direction, speed, Saffir-Simpson intensity and initial datums (in the case of the Lake Okeechobee and Cape Canaveral basins). In the example #2 above, (10 directions, 4 speeds and 5 Saffir-Simpson Categories), there would be 200 MEOWs.

4. Consolidate MEOW results, (if requested to do so by emergency officials), into maps of MEOWS Of MEOWS or MOMs. Typically, MOM 's depict surge flooding for each intensity ONLY, regardless of storm direction or speed. However, in other instances, the MEOWS of the two faster speeds** were consolidated to create five "FAST MOM's", while MEOWS of the two slower speeds were consolidated to create five "SLOW MOM's".

** Faster storms create higher surge on coastlines than do slower storms.  Slower storms create higher surge values further inland (because there is more time available to pump water) up rivers or into heads of bays, than do faster storms.

Simply put, the MEOW analysis represents the highest water* due to a "family" of parallel tracks with the same direction, speed and intensity.  The analysis is done for varying storm direction, speed of movement and category.  For example a MEOW exist for a Cat 4 storm moving from the east at 12 mph into the Miami SLOSH basin.  The MOM data is the "Maximum of Maximum or "Meows Of Meows" or the highest water* due to a composite of MEOWs.

This system includes the MOM data for all of the analyzed basins.  

IMPORTANT NOTE:  All of the SLOSH surge heights are referenced to NGVD - National Geodetic Vertical Datum (the mean sea level as determined in 1929.) This is the same reference the USGS uses for its quadrangle maps. So, when you see a 10 surge for a given area, you expect flooding up to the 10 foot contour on the quadrangle map at that location. Imagine that there's a 10 foot surge in an area.  One house has a base elevation of 11 feet, so it is "high and dry." But a neighboring house which is at 9 feet will get one foot of flooding in it's home.

Example of a Cat 4 MOM for Tampa Bay

For information on the SLOSH INUNDATION capabilities, see SLOSH Inundation Analysis.