Upon analysis of past hurricane paths and their relationship to the surrounding weather systems, a correlation can be found between hurricane tracks and the conditions in the temperate zone.
When a large area of low pressure exists to the west of a hurricane, the storm will at first be drawn toward this low-pressure region. Then the hurricane will be steered around the eastern edge of the low, where the winds come from the south. The hurricane moves northward into the belt of prevailing westerlies and finally turns to the northeast. The low-pressure area that causes this recurvature may be a broad tropical wave, a cyclone originating in the temperate zone, or another tropical cyclone.
Another scenario that often results in hurricane recurvature is the presence of a low between two highs on or near the continent. A hurricane in the Gulf of Mexico, for example, might turn northward and follow a break between two highs. This brings the storm into the belt of prevailing westerlies. It turns northeastward as it weakens over the land mass.
Still another possible recurvature situation exists when a break occurs in the Bermuda high. It is difficult to predict when such a break will occur, and if it does happen, it might not be well-defined enough to affect the track of a hurricane. But in some instances, storms follow such troughs. These conditions are often responsible for steering hurricanes near Bermuda and the Azores. Under these conditions, a hurricane can maintain much of its strength far into the northerly latitudes.
When the Bermuda high is especially large or strong, or is located somewhat to the west of its usual position, hurricanes normally do not recurve. The zone of the easterlies, or trade winds, expands farther north than usual. When this happens, hurricanes tend to travel in almost straight westerly or west-northwesterly paths. These nonrecurving storms can strike Central America or the Yucatan Peninsula. Occasionally they move into the Gulf and threaten Texas or Mexico.
The prevailing westerlies, which constantly fan the North American continent, sometimes slacken as a result of a massive high over the Great Plains or the southern United States. This kind of situation can prevent hurricanes from recurving. In 1980, Hurricane Allen was a nonrecurving storm. He eventually hit the Texas coast in a relatively unpopulated area. Allen was kept from recurving by high pressure to the north.
Hurricanes are steered, to a large extent, by the winds in which they are embedded. Forecasters can get a good idea of the future path of a tropical storm by locating the isobars over the North Atlantic and the North American continent. A hurricane usually, but not always, moves parallel, or nearly parallel, to the isobars in its vicinity. A fast-moving storm follows a more predictable path than a stalled or sluggish one.
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