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Have a spiral or circular system of strong winds rotating around an eye, sometimes hundreds of miles across in diameter. However, not all tropical cyclones become hurricanes or typhoons. They begin as Tropical Depressions, graduate to Tropical Storms when winds reach 39 miles per hour, and become hurricanes or typhoons at 74 mph, at which point they are classified by levels and additional titles.
The chart below shows how meteorologists in the US determine a hurricane's 'category', a measure of intensity. Hurricanes and typhoons begin to lose their strength once they hit land. Without the warm waters of the ocean to fuel them, they eventually decrease in both speed and size until they dissipate. Unfortunately, this doesn't always happen quickly enough to prevent irreparable damage. The American Red Cross provides disaster relief and assistance for both hurricanes and typhoons.
Hurricane Preparedness. A tropical storm with the wind speed of more than 34 kt is called a "typhoon" in Japan, while in the international standard, that with the wind speed of more than 64 kt is called a "typhoon. Joint Typhoon Warning Center JTWC and other US meteorological organizations use Saffir-Simpson Scale to classify tropical storms stronger than the hurricane or typhoon intensity based on the maximum sustained wind 1-min mean.
A typhoon with maximum sustained surface winds greather than or equal to knots approximately Category 5 is called a "super typhoon," and a hurricane of Category 3 and above is called a "major hurricane. In mainland China and Hong Kong, a typhoon with maximum sustained surface winds greather than or equal to knots are called Super Typhoon.
However, maximum sustained winds are measured differently in mainland China and Hong Kong, where the former uses 2-min mean and the latter uses min mean. In addition to maximum wind, maximum gust is also used to represent the strength of winds in a shorter time scale. Japan Meteorological Agency defines maximum gust as the average of 3 seconds the average of 12 measurements by the frequency of 0.
The ration of maximum gust divided by maximum wind is called "gust factor" and it is known to take some values between 1. For other regions than Japan and the United States, please refer to the classifiction of tropical cyclones in the world.
The intensity and size represents different aspect of a typhoon.
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