Due to the Earth's rotation, TCs tend to move from east to west and curve away from the equator. Third, inside the gathering cloud mass, there must be a moisture-laden layer at mid-troposphere altitude, 5 km (3 miles) above the ocean, to facilitate thunderstorm development.įourth, there must be a significant “Coriolis force” in effect. 1 Second, the atmosphere above the warm sea surface must cool rapidly with increasing vertical height this is necessary for transforming the ocean's heat energy into thunderstorms. TCs are monstrous heat engines, deriving their “fuel” from the warmth of the sea. First, TCs require warm ocean waters of at least 26.5 o C to a minimum depth of 50 m (165 feet). There are 6 necessary ingredients for TC formation. Depending upon the geographic locale, these powerful storms are labeled "hurricanes" in the North Atlantic, the Caribbean, the Gulf of Mexico, the eastern and central North Pacific, and along the west coast of Mexico "typhoons" in the western North Pacific and "cyclones" in the Indian Ocean and Australasia ( Fig. 1). With further intensification, TCs whose circulating wind speeds surpass 74 miles/hour (118 km/hour) achieve a special status and one of several monikers. If the rotating depression strengthens to the point where sustained surface winds reach 39 miles/hour (62 km/hour), the system becomes a named tropical storm. The direction of “spin” is counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Ī tropical system begins as a low-pressure trough (tropical wave) that develops into a moving concentration of thunderstorms (tropical disturbance) and begins to rotate with increasing velocity, ultimately forming a tropical depression. This composite of factors, including a warming planet, rising sea levels, and more frequent occurrences of “extreme” El Niño events, has implications for the disaster health of human populations, particularly for coastal and island residents living in areas that are regularly impacted by TCs. ![]() When considered in longitudinal perspective, the year 2015 represents the continuation of ongoing climate changes rather than an exceptional spike or aberration. Climate scientists are actively exploring the complex interactions and interrelationships among these climate patterns in relation to TC development, seasonal and long-term secular frequencies, storm strength, and locale of formation and maximal intensification. This convergence of elevated climate indicators appears to be affecting the frequency, intensity, and global geographic distribution of TCs. In 2015, increasing global temperatures and a vigorous El Niño are influencing the formation and movement of hurricanes, typhoons, and other tropical cyclones (TCs) worldwide. Rather than an aberration, these climate patterns of 2015 represent an ongoing trend with implications for the disaster health of coastal populations worldwide. Most notable among these, Hurricane Patricia formed on Octoand experienced extremely rapid intensification to become the strongest hurricane in the history of the Western Hemisphere and then weakened just as abruptly before dissipating on October 24, 2015. ![]() ![]() Warm Pacific Ocean temperatures, coupled with a strengthening El Niño, have supported the proliferation of Western North Pacific basin typhoons and Eastern/Central North Pacific Hurricanes. During the latter half of 2015, a very strong El Niño has formed and is predicted to build impressively, perhaps rivaling the memorable El Niño of 1997/1998. This year, 2015, is clearly on track to become the warmest on record in terms of global temperatures. The year 2015 is notable for the coincidence of several strong climate indicators that having bearing on the occurrence and intensity of tropical cyclones worldwide.
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