Example of storm surge

Other factors which can impact storm surge are the width and slope of the continental shelf. A shallow slope will potentially produce a greater storm surge than a steep shelf. For example, a Category 4 storm hitting the Louisiana coastline, which has a very wide and shallow continental shelf, may produce a 20-foot storm surge, while the same hurricane in a place like Miami Beach, Florida, where the continental shelf drops off very quickly, might see an 8 or 9-foot surge.

Surge animation with shallow continental shelf

Surge animation with steep continental shelf

Adding to the destructive power of surge, battering waves may increase damage to buildings directly along the coast. Water weighs approximately 1,700 pounds per cubic yard; extended pounding by frequent waves can demolish any structure not specifically designed to withstand such forces. The two elements work together to increase the impact on land because the surge makes it possible for waves to extend inland.

Although elevated, this house in North Carolina could not withstand the 15 ft. (4.5 m) of storm surge that came with Hurricane Floyd (1999)

Additionally, currents created by tides combine with the waves to severely erode beaches and coastal highways. Buildings that survive hurricane winds can be damaged if their foundations are undermined and weakened by erosion.

In confined harbors, the combination of storm tides, waves, and currents can also severely damage marinas and boats. In estuaries and bayous, salt water intrusion endangers the public health, kills vegetation, and can send animals, such as snakes and alligators, fleeing from flooded areas.

Surge Vulnerability Facts

• From 1990-2008, population density increased by 32% in Gulf coastal counties, 17% in Atlantic coastal counties, and 16% in Hawaii (U.S. Census Bureau 2010)

• Much of the United States' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level

• Over half of the Nation's economic productivity is located within coastal zones

• 72% of ports, 27% of major roads, and 9% of rail lines within the Gulf Coast region are at or below 4 ft elevation (CCSP, SAP 4-7)

• A storm surge of 23 ft has the ability to inundate 67% of interstates, 57% of arterials, almost half of rail miles, 29 airports, and virtually all ports in the Gulf Coast area (CCSP SAP 4-7)

Notable Surge Events

Ike 2008 (SLOSH Historical Run)
Hurricane Ike made landfall near the north end of Galveston Island as a Category 2 hurricane. Storm surges of 15-20 feet above normal tide levels occurred along the Bolivar Peninsula of Texas and in much of the Galveston Bay area. Property damage from Ike is estimated at $24.9 billion. More...

Katrina 2005 (SLOSH Historical Run)
Katrina was one of the most devastating hurricanes in the history of the United States. It produced catastrophic damage - estimated at $75 billion in the New Orleans area and along the Mississippi coast - and is the costliest U. S. hurricane on record. Storm surge flooding of 25 to 28 feet above normal tide levels was associated with Katrina. More...

Dennis 2005 (SLOSH Historical Run)
Dennis affected much of Florida, and its effects extended well inland over portions of the southeastern United States with the maximum amount rainfall of 12.80 inches occuring near Camden, Alabama. Storm surge flooding of 7-9 ft produced considerable storm surge-related damage near St. Marks, Florida, well to the east of the landfall location. The damage associated with Dennis in the United States is estimated at $2.23 billion. More...

Isabel 2003 (SLOSH Historical Run)
Isabel was the worst hurricane to affect the Chesapeake Bay region since 1933. Storm surge values of more than 8 feet flooded rivers that flowed into the bay across Virginia, Maryland, Delaware, and Washington, D.C. Isabel was the most intense hurricane of the 2003 season and directly resulted in 17 deaths and more than $3 billion in damages. More...

Opal 1995 (SLOSH Historical Run)
Hurricane Opal made landfall near Pensacola Beach, Florida as a Category 3 hurricane. The storm caused extensive storm surge damage from Pensacola Beach to Mexico Beach (a span of 120 miles) with a maximum storm tide of 24 feet, recorded near Fort Walton Beach. Damage estimates for Opal were near $3 billion. More...

Hugo 1989 (SLOSH Historical Run)
Hugo impacted the southeastern United States, including South Carolina cities Charleston and Myrtle Beach. Hugo was responsible for 60 deaths and $7 billion in damages, with the highest storm surge estimated at 19.8 feet at Romain Retreat, South Carolina. More...

Camille 1969 (SLOSH Historical Run)
Camille was a Category 5 hurricane, the most powerful on the Saffir-Simpson Hurricane Wind Scale with maximum winds of more than 155 mph and storm surge flooding of 24 feet that devastated the Mississippi coast. The final death count for the U.S. is listed at 256. This includes 143 on the Gulf coast and another 113 from the Virginia floods. More...

Audrey 1957 (SLOSH Historical Run)
There were 390 deaths associated with Audrey as the result of a storm surge in excess of 12 feet, which inundated the flat coast of southwestern Louisiana as far as 25 miles inland in some places. More...

New England 1938 (SLOSH Historical Run)
The Long Island Express was a fast-moving Category 3 hurricane that struck Long Island and New England with little warning on September 21. A storm surge of 10 to 12 ft inundated the coasts of Rhode Island, Connecticut, southeastern Massachusetts, and Long Island, NY, especially in Narragansett Bay and Buzzards Bay. Six hundred people died due to the storm. More...

Galveston 1900 (SLOSH Historical Run)
At least 8,000 people died when hurricane storm tides (the surge plus the astronomical tide) of 8-15 feet inundated most of the island city of Galveston, TX and adjacent areas on the mainland. More...

FAQ

What is storm surge inundation?
This is simply referencing storm surge as height above ground level. For the SLOSH model, this is done by subtracting the average elevation of each SLOSH grid cell from the water level computed by the SLOSH model which is referenced to a vertical datum. This helps to alleviate the confusion inherent with vertical datums. Now, when we say twenty feet of water, we mean twenty feet above ground level.

Storm Surge Inundation

How is storm surge observed and measured?

• Tide Stations (NOAA): A network of 175 long-term, continuously operating water level stations throughout the U.S. serving as the foundation for NOAA's tide prediction products and providing data for storm surge estimates.

NOAA Tide Station

• Measure still water (e.g., no waves)

• Traditionally most reliable

• Limited stations

• FEMA/USGS High Water Marks (HWM):
  These marks are lines found on trees and other structures marking the highest elevation (peak) of the water surface for a flood event created by foam, seed, or other debris. Survey crews are deployed after a storm to locate and record reliable HWMs. GPS methods are used to determine location for coastal HWMs, which are then mapped relative to a vertical reference datum such as NAVD88.

High Water Marks Inside A Building

• Perishable

• Traditionally best method for capturing highest surge

• Subjective and often include impacts of waves

Pressure Sensors (USGS):
These are temporary water-level and barometric-pressure sensors which provide information about storm surge duration, times of surge arrival/retreat, and maximum depths.

USGS Pressure Sensor

• Relatively new method

• Deployed in advance of storms at expected location of highest surge

• Can contain impacts of waves

Where can one find storm surge data and storm related products during a tropical event?

• Probabilistic Surge (P-Surge): nhc.noaa.gov

• NHC Public Advisories: nhc.noaa.gov

• WFO Products: weather.gov

• NOAA Tide Stations: tidesonline.nos.noaa.gov

The storm surge interactive risk maps show storm surge risk as a function of categories in the Saffir-Simpson Hurricane Scale. How is this possible considering the recent removal of storm surge from the Saffir-Simpson Scale?

• Earlier versions of the Saffir-Simpson Hurricane Scale incorporated storm surge as a component of each category. Storm surge was quantified by category in the earliest published versions of the scale dating back to 1972. However, hurricane size (extent of hurricane-force winds), local bathymetry (depth of near-shore waters), topography, the hurricane's forward speed and angle to the coast also affect the surge that is produced. For example, the very large Hurricane Ike (with hurricane force winds extending as much as 125 mi from the center) in 2008 made landfall in Texas as a Category 2 hurricane and had peak storm surge values of about 20 ft. In contrast, tiny Hurricane Charley (with hurricane force winds extending at most 25 mi from the center) struck Florida in 2004 as a Category 4 hurricane and produced a peak storm surge of only about 7 ft. These storm surge values were substantially outside of the ranges suggested in the original scale. Thus to help reduce public confusion about the impacts associated with the various hurricane categories as well as to provide a more scientifically defensible scale, the storm surge ranges have been removed from the scale and only peak winds are employed in the Saffir-Simpson Hurricane Wind Scale.

Unlike earlier versions of the Saffir-Simpson Hurricane Scale which only provide average storm surge values by category, the storm surge interactive risk maps show potential storm surge vulnerability for all areas and incorporate varying landfall locations, local bathymetry and topography, varying storm sizes, forward speeds, tracks, approach angles, and tide levels. This is accomplished by performing thousands of different SLOSH simulations for a given area and then compositing the results into a worst case snapshot, by Saffir-Simpson Category, indicating storm surge vulnerability. Thus, for a given area of interest, the storm surge interactive risk maps make use of thousands of hurricane landfall scenarios.

The storm surge interactive risk maps are different from my local hurricane evacuation zones. Which is correct?

• Under no circumstances should the storm surge interactive risk maps be compared with local hurricane evacuation zones. Hurricane evacuation zones consider other critical factors which affect hurricane evacuation decision-making. These maps are provided for informational and educational purposes only and do not supersede hurricane evacuation zones set by local and state emergency management.

According to the storm surge interactive risk maps, I live along the edge of an area susceptible to inundation. Does this mean my home is safe from the potential impacts from storm surge?

• No. Points of interest that are displayed as dry but are close to the edge of an inundated area should also be considered extremely vulnerable to hurricane storm surge. As an example, in the accompanying illustration the actual model data do not show the red areas as inundated. Yet they are as vulnerable to storm surge as are the actual inundation areas, which are shown in yellow.

Example: Additional Areas Vulnerable to Storm Surge Inundation

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