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Geosciences LibreTexts

Special Topic: Hurricanes

Hurricanes are extreme tropical storms that form in the ocean. They are referred to as tropical cyclones or typhoons depending on the region. Hurricanes begin as tropical disturbances, which is the slight circulation in low-pressure areas of warm seawater. A disturbance then becomes a tropical depression when winds increase in speed to at least 38 mph, which create a drop in pressure in the center of the depression. If wind speed increases to 39 mph it then becomes a tropical storm, and when a storm reaches wind speeds of 74 mph it becomes a hurricane. They receive names that identify them when they become storms and then keeps those names as hurricanes. The winds create a rotation around the central core (eye) of the storm.

Hurricanes can reach speeds of 160 mph and produce up to 2.4 trillion gallons of rain a day. They are rated 1-5 based on the Saffir-Simpson scale. This is scale is determined by the intensity of the winds of a hurricane. The highest category, which is 5, is reserved for hurricanes that reach speeds of 157 mph and greater. This scale also helps to determine the possible damage on land by a hurricane.

he average annual economic loss is estimated at some 5% of the gross national income. 45 tropical storms reach hurricane strength each year on average, 30% of them in the western North Pacific. Due to the short period in which observations can be made, Because of the short period of reliable observations, it is not yet feasible to determine a trend or reliable low-frequency variations. There is a variability and shifts in the number of major hurricanes in the Atlantic and the Caribbean.Superimposed on this slow variability are substantial variations from year to year, often influenced by El Niño-Southern Oscillation (ENSO) events.