Hurricanefacts • Tropical cyclones are called hurricanes in the Atlantic and typhoons in the Pacific. • Hurricanes rotate anti-clockwise in the northern hemisphere, and clockwise in the southern hemisphere. • For a hurricane to form, ocean temperature must be at least 26½°C down to a depth of at least 50m. • One third of Atlantic hurricanes form in September, and three quarters between August and October.
Hurricane force: Force 1 (minimal): 74-95mph [110 have hit the US since 1851, 1 of them this year] Force 2 (moderate): 96-110mph [72 have hit the US since 1851] Force 3 (extensive): 111-130mph [73 have hit the US since 1851, 2 of them this year] Force 4 (extreme): 131-155mph [19 have hit the US since 1851, 1 of them this year] Force 5 (catastrophic): 156+mph [3 have hit the US since 1851 - in 1935, 1969 and 1992]
• Hurricane Able was the first named hurricane, in 1950. • Only female names were used from 1953 until 1979 - now hurricanes alternate in gender. • A list of 21 names is picked for each hurricane season. Lists repeat every 6 years. • This year's list will be reused in 2011, but Katrina and Rita will almost certainly be retired. • There are only four names left on this year's list. If the names run out (which would be the first time ever) then Greek letters will be used instead.
