Windswept_ The Story of Wind and Weather - Marq de Villiers [84]
In the eastern Pacific, most hurricanes fizzle harmlessly in the colder water west of the Americas. Hawaii gets a few, but the prevailing easterlies steer most of them well south of the islands. The north and western Pacific is even more prone to cyclones than the Caribbean, and the "season" is yearlong and therefore much more dangerous than the six months or so of the Atlantic. Pacific typhoons are born at sea, and tend to be larger and better organized than their Atlantic cousins—the much greater stretch of the Pacific gives them substantially more room to mature than the smaller Atlantic. The classical Japanese description of a typhoon is kamikaze, or "divine wind"; Japan and the Philippines are frequently assaulted by three or more storms a year—Japan had ten in 2004. Korea, China, and Vietnam are also vulnerable. To the south, Australia's northern littoral is under threat from typhoons in summer and fall, from December through about May; about a dozen cyclones a year form offshore, and some of them strike land. The worst storm in Australian history was Tracy, which struck Darwin on Christmas Day 1974. New Zealand's waters are too cool for tropical cyclones, but like Maritime Canada the islands are prone to strong extratropical frontal storms as the cyclones wind down.18 Pacific typhoons are tracked by storm centers in many places around the ocean's rim, but the most active are the Typhoon Center in Tokyo and a facility run by the U.S. Navy in Pearl Harbor, Hawaii. One of the oldest weather offices in the world was set up by the British in Hong Kong in 1884; the Chinese are still using it to track typhoons.
A precondition for the transformation of a line of thunder cells or a low-pressure wave into a tropical cyclone is stable air, a local environment where the winds don't change very much. Hurricanes don't form in patches of turbulent or active air—powerful as they are, destructive as they are, they are also curiously vulnerable at birth. There must be very little wind shear, allowing the big cumulus thunderstorms to build vertically. Any strong wind above a hurricane will destroy it, either by tipping it over through shear, or by literally poking holes in the warm core tube, allowing the warm air to vent, which weakens it. Or they'll "plug the chimney" at the top, where the storm's vent is.
Another precondition is warm water. The ocean below must be at least 260 Celsius, but preferably 26.50 or higher. No real scientific consensus exists on why this number is the magic one. It has perhaps to do with the climatological factors governing tropical oceans, but which factors and precisely how are still unknowns. Temperatures can be higher than 26°, but not lower—the higher they are, the greater the potential for damaging convection currents to occur. Higher temperatures don't increase the probability that a system will coalesce into a hurricane, but they do tend to make that hurricane more intense.
If these preconditions are met, the winds of the passing thunderstorms, still just a tropical disturbance or tropical wave, will evaporate this warm water, and because of the Coriolis force, the winds will lazily circle inward to the center. This causes a small vacuum, and the pressure drops, driving the warm, moist air upward. At about 2.4 miles above the surface, the vapor begins to condense into water, or into shards of ice and wet snow, and the act of condensation causes something deadly to happen: The heat, and therefore the latent energy contained in the moist air, is released. This