An example of the new storm surge hazard map being developed by the National Hurricane Center shows potential flooding in Florida. (NHC Storm Surge Unit)
Along the coast… storm surge is often the greatest threat to life and property from a hurricane. In the past… large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall.
However... many people do not understand this term or the threat it represents. So what exactly is a storm surge? It is the abnormal rise of water generated by a tropicalstorm or hurricane… over and above the predicted astronomical tides.
Storm surge should not be confused with storm tide… which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide… resulting in storm tides reaching up to 20 feet or more in some cases.
Storm surge is produced by water being pushed toward the shore by the force of the winds moving cyclonically around the storm. The impact on surge of the low pressure associated with intense storms is minimal in comparison to the water being forced toward the shore by the wind.
So… here is the deal. NOAA is rolling out a new tool at the National Hurricane Center this year.
The tool… beginning with this hurricane season… is a potential storm surge flooding map for those areas along the Gulf and Atlantic coasts of the United States at risk of storm surge from a tropical cyclone.
The map will be issued for coastal areas when a hurricane or tropical storm watch is first issued… or approximately 48 hours before the anticipated onset of tropical storm force winds.
Developed over the course of several years in consultation with emergency managers… broadcast meteorologists and others… this new map will show:
• Geographical areas where inundation from storm surge could occur.
• How high above ground the water could reach in those areas.
The Potential Storm Surge Flooding Map is an experimental National Weather Service product that provides valuable new information on the storm surge hazard associated with tropical cyclones.
Here are some things to know about this map:
• The first map will usually be issued at the same time as the initial hurricane watch… or… in some cases, with a tropical storm watch. The map is based on the latest forecast track and intensity for the tropical cyclone… and takes into account likely forecast errors.
• The map shows inundation levels that have a 10 percent chance of being exceeded… and can therefore be thought of as representing a reasonable worst-case scenario for any given location.
• The map is subject to change every six hours in association with every new NHC full advisory package. Due to the processing time required to produce the map… it will not be available until about 45 to 60 minutes following the advisory release.
The map will be part of an interactive display made available on the NHC website (www.hurricanes.gov) in situations where hurricane watches and warnings are in effect for portions of the continental U.S.
A great resource for you to save on your favorites is the WSAV Tropical Page... where we detail all your local tropical weather. Check it out if you haven't already!