Less commonly publicized than the effects from tropical cyclones, Extratropical Storm Surge can be just as destructive, and much more frequent in certain coastal communities. For an overview of storm surge, please see the parent article.
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Similar to tropical cyclones, extratropical storms cause an offshore rise of water. High winds pushing on the ocean's surface create storm surge by causing the water to pile up higher than the ordinary sea level. However, unlike most tropical cyclone storm surge, extratropical storms can cause higher water levels across a large area for longer periods of time, depending on the system. This is due to many factors, such as storm size and different steering winds, which could keep a system in a storm-surge prone area for longer periods of time.
Additionally, a common but frequently overlooked component of extratropical storm surge is the phenomenon of negative water levels. If strong winds are blowing offshore, situations can arise where mean water levels in a bay fall significantly, which poses a serious threat for ships tied up at piers. If negative water levels are severe enough, ships tied up at docks can actually sit on the seafloor, preventing them from leaving port.
Extratropical storm surge, although not a common event in some basins, especially on the US East Coast, is mentioned in guidance from the National Weather Service Ocean Prediction Center for the Pacific & Alaska coasts, and North of 31°N on the Atlantic Coast. The National Hurricane Center, to a lesser extent, mentions extratropical storm surge for the Gulf coast states mostly during the wintertime, when extratropical cyclones affect the coast.
The National Weather Service Meteorological development laboratory in Silver Spring MD has developed an extratropical storm surge model with different domains of US coastline. Similar to the SLOSH model, the ETSSM runs off of the GFS computer model, and can provide guidance on above or below average water levels in a certain geographical domain as the result of a storm system's influence. Its resolution however, is more coarse than most of the specific SLOSH domains because it covers regions as opposed to small-scale basins that can be affected by landfalling tropical cyclones.
Although extratropical storm surge is not officially forecast, it is mentioned in guidance from the Ocean Prediction Center in the marine weather discussions, and in coastal flood advisories issued by local NWS weather forecast offices.
November 9-13, 2009 marked a significant extratropical storm surge event on the US east coast. The extratropical remnants of Hurricane Ida developed into a Nor Easter off the Southeast US coast. During the event, storm force winds from the E were present along the northern periphery of the low pressure center for a number of days, forcing water into locations such as Chesapeake Bay. Water levels rose significantly, and remained as high as 8 feet above normal in numerous locations throughout the Chesapeake for a number of days as water was continually built-up inside the estuary from the onshore winds and freshwater rains flowing into the bay. In many locations, water levels were shy of records by only a tenth of a foot.