A hurricane is a Tropical cyclone that occurs when an area of intense low pressure develops over warm ocean waters in tropical regions in summer and early autumn. It is a revolving storm originating at latitudes between 5° and 20° north or south of the Equator, usually when the surface temperature of the ocean is above 26°C/79°F. A central calm area, called the eye, is surrounded by inwardly spiralling winds (anticlockwise in the northern hemisphere and clockwise in the southern hemisphere) of up to 320 kph/200 mph. A hurricane is accompanied by lightning and torrential rain, and can cause extensive damage. In meteorology, a hurricane is a wind of force 12 or more on the Beaufort scale. A tropical cyclone that occurs in the western part of the North Pacific is called a typhoon.
Hurricanes are categorized by the maximum sustained wind speed that they produce. Category 1 storms have a wind speed range of 119–53 kph/74–95 mph. The highest category storms, category 5, have sustained wind speeds in excess of 249 kph/155 mph.
The naming of hurricanes began in the 1940s with female names. Owing to public opinion that this was sexist, the practice was changed in 1978 to using male and female names alternately.
Hurricane Katrina is the costliest natural disaster in the history of the USA. It formed over the Bahamas in August 2005 and strengthened to a category 5 storm with maximum sustained wind speeds of 280 kph/175 mph, causing severe damage along the Gulf coast of the USA. Although weakened to a category 3 storm when it moved inland, Katrina's winds were strong enough to cause the levees in New Orleans to fail, resulting in the flooding of 80% of the city and surrounding districts. An estimated 1,836 people died as a result of the storm and there was over $81 billion of property damage.