Hurricanes are defined by their strong winds. But the storm surges they cause can often be just as devastating in coastal communities.
Henri, which turned into a hurricane Saturday morning with winds of 75 miles per hour, was expected to cause dangerous storm surges in parts of Long Island, Connecticut, Massachusetts and Rhode Island.
Storm surge is defined as an anomalous rise in ocean level caused by a storm, on top of the predicted astronomical tide. The waves are caused by ocean water moving inland, propelled by the force of the wind.
In the open ocean, hurricanes can pound the water without creating a wave. But near the coast, the shallower water is blown inland, threatening property and lives.
The deepest water will be along the immediate coast in areas with onshore winds, where the wave will be accompanied by large and dangerous waves, the National Hurricane Center said.
Flood-related flooding depends on wave timing and tidal cycle, and can vary widely over short distances, the center said.
In 2008, Ike, a Category 2 hurricane that made landfall near Galveston Island in Texas, caused spikes 15 to 20 feet above normal tides, the center said. Property damage was estimated at $24.9 billion.
Henri, a Category 1 storm, was expected to create a storm surge of up to 1.5 meters, meaning the water could rise 1.5 meters above the normally predicted astronomical tide.
The National Hurricane Center said areas placed under a storm surge warning are at risk of “life-threatening flooding.” People in those areas must follow all evacuation instructions from local officials, the center said.