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Why do Hurricanes Hit the East Coast of the U.S. but Never the West Coast?

Chris W. Landsea is a researcher at the Atlantic Oceanographic and Meteorological Laboratory/Hurricane Research Division of the National Oceanic and Atmospheric Administration (NOAA), located in Miami, Fla. He replies:

"Hurricanes form both in the Atlantic basin, to the east of the continental U.S. (that is, in the Atlantic Ocean, the Gulf of Mexico and the Caribbean Sea), and in the Northeast Pacific basin, to the west of the U.S. The hurricanes in the Northeast Pacific almost never hit the U.S., however, whereas the ones in the Atlantic basin strike the U.S. mainland just less than twice a year on average.

"There are two main reasons for this disparity. The first is that hurricanes in the northern hemisphere form at tropical and subtropical latitudes and then tend to move toward the west-northwest. In the Atlantic, such a motion often brings the hurricane into the vicinity of the East Coast of the U.S. In the Northeast Pacific, the same west-northwest track carries hurricanes farther offshore, well away from the U.S. West Coast.

"The second factor is the difference in water temperatures along the U.S. East and West coasts. Along the East Coast, the Gulf Stream provides a source of warm (above 80 degrees Fahrenheit, or 26.5 degrees Celsius) waters, which helps to maintain the hurricane. Along the West Coast, however, ocean-surface temperatures rarely rise above the lower 70s F. (the low 20s C.), even in the middle of summer. Such relatively cool temperatures do not provide enough thermal energy to sustain a hurricane's strength. So the occasional Northeast Pacific hurricane that does track back toward the U.S. encounters the cooler waters of the Pacific, which can quickly reduce the storm's strength."

Kerry Emanuel in the Center for Meteorology and Physical Oceanography at the Massachusetts Institute of Technology expands on the details of hurricane behavior:

"Hurricanes almost always form over ocean water warmer than about 80 degrees F. in a belt of generally east-to-west flow called the trade winds. They move westward with the trade winds and also drift slowly poleward. Eventually, if they last long enough, they will drift poleward far enough to enter the belt of westerly winds that prevails in middle latitudes. When this happens, the hurricanes 'recurve' toward the east and thereafter follow paths that are generally both eastward and poleward.

"In the Atlantic region, hurricanes form anywhere from the tropical central Atlantic to the Gulf of Mexico. Those that form in the central Atlantic and Caribbean region usually start off moving westward; when they recurve, they may strike the North American mainland. Some of the storms that begin in the Gulf of Mexico may move poleward and eastward right from their inception.

By Chris W. Landsea

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