Storm Surge vs. Storm Tide

• Storm Surge: Water that is pushed toward the shore by the force of winds swirling around a storm.
• Storm Tide: The combination of the normal tide and the storm surge to create the total increase in water level due to the storm. The tide level when a hurricane makes landfall can have a major impact on the total water surface elevation.

How the SLOSH Model Works

Given a specific geographic region (a SLOSH Basin), the model takes a hypothetical or historical hurricane track and calculates the resulting storm surge.

Model Inputs:

• Hurricane Pressure.
• Forward Speed.
• Direction and Location.
• Radius of Maximum Winds.
• Basin Topography and Bathymetry (water depth relative to mean sea level).

Model Accuracy and Limitations:

• Accuracy is generally within +/- 20% of the peak storm surge for a known hurricane track, intensity, and size.
• The model accounts for astronomical tides by either (a) specifying the initial tide level, or (b) using a spatial and time varying tidal calculation based on ADCIRC’s EC2015 tidal harmonics.
• The model does not include rainfall amounts, river flow, or wind-driven waves.

Storm Surge Generalizations

When observing storm surge animations, several meteorological generalizations apply:

1. More intense storms cause higher surges.
2. The highest surges usually occur to the right of the storm track.
3. Fast-moving storms cause high surges along the open coast and lower surges in sheltered bays and estuaries.
4. Slow-moving storms usually result in greater flooding inside bays and estuaries, with smaller values along the open coast.
5. Larger storms (greater radius of maximum wind) affect longer stretches of the coastline.
6. A shallow coastal slope will allow a greater storm surge with small waves, while areas with steep coastal slopes experience less surge but large breaking waves.

Interpreting Rexfiles and Wind Data

A Rexfile contains SLOSH-generated water level heights at each grid cell and hurricane wind parameters for specific time intervals. When animating a Rexfile in the SDP, wind speeds and directions are displayed using standard meteorological conventions:

Wind Barb Symbology:

• Short Barb: 5 knots.
• Full Barb: 10 knots.
• Triangular Flag: 50 knots.
• Example: A wind flag showing a triangle, two full barbs, and one half barb indicates a wind speed of 75 knots. Direction is indicated by the direction of the wind barb itself.

Wind Scale Colors:

• Green: Tropical storm force to hurricane force winds.
• Red: Hurricane force up to 100 knots (Category 3).
• Black: Categories 3, 4, and 5.