8. Can surges be predicted?

Yes. Weather forecasts particularly through mathematical modelling are now sufficiently good to predict surges and they are constantly being improved. The main problem with forecasts of such hazards is the system’s ability to adequately disseminate this information. A number of models are used e.g. the WES Implicit Flooding Model and the SLOSH model used by the US National Weather Service for real time forecasting. The main data inputs require minimum central pressure, radius, storm track and speed. Other models also exist, e.g. Hubbart and McInnes, (1997) which treats the land-water boundary as a moving interface, inland grid cells flooding as the water level rises.

Emmanuel et al, (2008) via model estimates achieved from simulations of 2000 storm tracks indicate that storm/surge frequency will decrease in the Southern Hemisphere and north Indian Ocean, whilst increasing in the western North Pacific. Simulations show that changes in tropical cyclone activity is highly influenced by an increasing difference as climate warms between the moist entropy of the boundary layer and that of the middle troposphere. The model uses ‘a specialized, coupled ocean–atmosphere hurricane model phrased in angular momentum coordinates, which provide a high resolution of the core at low cost’.

Kerry Emanuel, Ragoth Sundararajan, and John Williams, 2008. Hurricanes, and Global Warming: Results from Downscaling IPCC AR4 Simulations, Bulletin of the American Meteorological Society, 89(3) 47–367

The Sea, Lake, and Overland Surge from Hurricanes (SLOSH) model

  • Provides real time forecasting and hurricane storm surge inundation maps for the U.S. Atlantic coast, Oahu, the Bahama Islands, Puerto Rico, and the Virgin Islands. (source: http://www.wunderground.com/hurricane/surge_images.asp).
  • Accuracy of the SLOSH model is advertised as +/- 20%. It provides 2 sets of images:
  • Maximum Water Depth“ – water depth at each grid cell of the SLOSH domain. Thus if inland at elevation of 10ft > MSL, and combined storm surge and tide ( “storm tide”) is 15ft at your location, then the water depth image will show 5ft of inundation.
  • Maximum Storm Tide“ – how high above mean sea level the sum of the storm surge plus the tide reaches.
  • Over the ocean, the storm tide and water depth images will show the same values.
  • Images are generated for high tide, thus showing worst-case inundation scenarios for mid-strength hurricanes of each Saffir-Simpson Category (1- 5).

However, the US National Hurricane Center no longer includes storm surges and flooding for hurricane categories stating that people are not acting upon warnings. In part, this may be a result of past discrepancies that have occured between forecasted and actual. For example, Hurricane Ike, a Category 2 on the Saffir-Simpson scale, had winds of 96-110 mph, and a storm surge of 3.5 – 6.8m. The forecasted storm surge was of a Category 5 storm i.e. winds greater than 155 mph. A Category 2 hurricane, on the Saffir-Simpson scale, has a storm surge of 6 to 8 feet. (1.8 to 2.8m)