Hurricane Dangers: Storm Surge
A hurricane’s storm surge is the mass of water from the ocean pushed on shore as a hurricane makes landfall.
Hurricane intensity, forward speed, size, central pressure, shape, and angle of approach to the coast all determine how strong the surge will be.
Waves move on top of the surge and cause even more damage by acting as battering rams to flooded structures. Water weighs about 1700 pounds per cubic yard, so it can easily demolish buildings.
A storm surge undermines roads and foundations when it erodes material out from underneath them.
This advancing surge of water moving ahead of a hurricane can combine with the normal tides to create the hurricane storm tide, which can increase the mean water level to heights that impact roads, homes and other critical infrastructure. Many buildings withstand hurricane force winds until their foundations, undermined by erosion, are weakened and fail.
The all-time record for highest U.S. storm surge is Hurricane Katrina’s 27.8 feet in Pass Christian, Mississippi in 2005 (measured from a “still water” mark found inside a building where waves couldn’t reach). However, the highest high-water mark from Katrina was much higher: a mind-boggling 34.1 feet above mean level, measured on the outside of a building in Biloxi, Mississippi, where a high tide of about 1 foot combined with 11-foot high waves on top of the 22-foot storm surge to create the 34.1-foot high water mark.
According to a database of high water marks of landfalling U.S. hurricanes from 1933 – 2017 compiled by Katie Peek of Western Carolina University, the peak high water marks of 20.6′ - 21.2′ in Mexico Beach would put Hurricane Michael in fifth or sixth place for highest water levels ever recorded from a U.S. landfalling hurricane since 1933.
|Hurricane||High Water Mark|
|Katrina (Cat 3), 2005||34.11’ above MSL at Biloxi, MS|
|Camille (Cat 5), 1969||24.6’ above MSL at Pass Christian, MS|
|Carla (Cat 4), 1961||22’ above MSL at Calhoun County, TX|
|Opal (Cat 3), 1995||21.5’ above MSL at Mirimar Beach, FL|
|Michael (Cat 5), 2018||20.6′ - 21.2’ above MSL at Mexico Beach, FL|
|Irene (Cat 1), 2011||20.77’ above NAVD at Lido Beach, NY|
|Audrey (Cat 3), 1957||20.3’ above MSL at St. James Parrish, LA|
|Hugo (Cat 4), 1989||20.2’ above NGVD at Awendaw, SC|
|Isaac (Cat 1), 2012||19.7’ above NAVD at Harrison County, MS|
|Ike (Cat 2), 2008||19.4’ above NGVD at High Island, TX|
The shape of bays and estuaries and slope of the ocean bottom play a large role in how bad a storm surge an area will receive.
Coastlines such as those along the Gulf of Mexico coast from Texas to Florida have long, gently sloping shelves and shallow water depths. These areas are subject to higher storm surges, but smaller waves. This difference is because in deeper water, a surge can be dispersed down and away from the hurricane. However, upon entering a shallow, gently sloping shelf, the surge cannot be dispersed away, but is driven ashore by the wind stresses of the hurricane.
Coastal areas with a steeply sloping ocean bottom will experience less surge than areas next to shallow slopes, given the same storm.
In the United States and many other countries, the storm surge is not the primary cause of death associated with hurricanes. In fact, in the past twenty years, just over 1% of hurricane-related deaths in the United States have been caused by a storm surge. The majority of hurricane deaths in the United States come from inland flooding.
In other parts of the world, however, virtually all hurricane-related deaths are a result of storm surges. Bangladesh is the area in the world most affected by the storm surge, with over a hundred on record. These storm surges are responsible for hundreds of thousands of deaths in the Bangladesh area alone.
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Background Picture: Water from Roanoke Sound pounds the Virginia Dare Trail in Manteo, N.C., Saturday, Sept. 3, 2016 as Tropical Storm Hermine passes the Outer Banks. (AP Photo/Tom Copeland)