11 • Continued from previous page of the Equator. Almost 100 such storms occur globally each year. These weather systems are remarkably similar in how they are created but they are called by different names in different parts of the world as we show below. AREA OF THE WORLD Atlantic Basin and the Caribbean Eastern, Northern Pacific Ocean Western Pacific Ocean Southern Hemisphere Australia (informally) NAMES GIVEN TO CYCLONES Hurricanes Hurricanes Typhoons Cyclones Willy-willy The table illustrates the fact that Tropical Cyclones are found in both the Northern and Southern Hemisphere. Caribbean countries are located north of the equator and south of the Tropic of Cancer (23.5° north). That means that they are in the Northern Hemisphere. Professor Stephen Nelson of Tulane University estimates that 12% of tropical cyclones arise in the Atlantic Ocean while 15% develop in the Eastern Pacific Ocean, 30% in the Western Pacific, 24% in the Indian Ocean and 12% in the southern Pacific Ocean. There is now broad agreement on the conditions that create these storms. They include: • Warm ocean water of at least 80° Fahrenheit • Enough moisture in the atmosphere to sustain the storm • An initial atmospheric disturbance such as an Easterly Wave, in which warm, moist air converges and circulates • Very little wind shear in the upper atmosphere In the Atlantic Basin and the Caribbean region, the storms that can become hurricanes, occur most frequently during the designated hurricane season that extends from June 1st to November 30th. There is a statistical peak in September. The Caribbean is particularly vulnerable to hurricanes due to its location in the Atlantic “hurricane belt”. While the hurricane season extends from June to November, such storms can occur throughout the year. There has been at least one hurricane-type storm in each month of the year. In the eastern, Northern Pacific Ocean region, the storms are most common from May to November. There is a contrast with the Indian Ocean. In that area, the storms are common from April until December. Strikingly, there is a double peak in storm activity, one in May and another in November each year. It is notable that with the reversal of seasons in the hemispheres, storms in the Southern Hemisphere are more common closer to the end of the calendar year or early in the year – from November to April. The following classification of Tropical Cyclones was taken from the World Meteorological Organisations 2023 fact sheet. • Continues on next page
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