National Weather Service United States Department of Commerce

What Causes Surge?

Strong hurricane winds blow along the ocean surface and cause water to pile up as it approaches the shoreline. Low pressure at the storm's center causes water to bulge upward. The surge effect from wind is much higher than that caused by low pressure.

Storm intensity, forward speed, size, central pressure, shape, and angle of approach to the coast all determine how strong the surge will be. The shape of bays and estuaries and slope of the ocean bottom also play a large role

Coastal areas adjacent to a steeply sloping ocean bottom will experience less surge than areas adjacent to shallow slopes, given the same storm.

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. Surge undermines roads and foundations when it erodes material out from underneath them. It can also send salt water into the fresh drinking supply and drives potentially dangerous creatures inland to higher ground.


Storm Surge vs Storm Tide

Storm surge is purely water level rise caused by hurricane winds and low pressure. However, when surge levels are combined with the already-present tide, "storm surge" becomes "storm tide".

If storm surge hits a coastal area during its high tide, it can cause even more damage. That phenomenon motivates research into improving surge predictions by accurately modeling the timing of peak surge in relation to astronomical tides.


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