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the mariner had to rely on his observations of the sea and sky. Gathering clouds, a change in swell direction, a falling barometer—these were potential warning signs. Knowing that a storm was coming was no guarantee of safety, because ship captains never knew for sure what direction the storm would take. Their ships were almost always too slow to outrun a storm, so unless there was a safe port nearby, they had no choice but to secure their vessels as best they could, shorten sail, and ride it out. Even today, with the latest weather and storm forecasting computer models, there is no guarantee that a given storm will behave as predicted.
Tropical storms originate in specific areas of the oceans where sea and wind conditions are suitable. They also generally occur at specific times of the year. For example, in the North Atlantic and the Caribbean—from Venezuela on the south to the East Coast of the United States and Central America on the west, Newfoundland on the north, and eastward to Africa—they occur from June 1 to November 30 and peak from August to October. The specific times for other major ocean basins are available in the literature.
The frequency of storms varies with location and from year to year. The western North Pacific is the most prolific source of tropical cyclones, averaging about 25 per year, approximately 18 of which become typhoons. Long-term records show that the frequency of hurricanes increases in some years and decreases in others, generally on a scale of decades. For example, 1991 to 1994 were “quiet years” in the North Atlantic and Caribbean, while post-1995 has seen an increase in activity. In Australia a downward trend has been observed, while in the Northwest Pacific the trend has been up. Likewise, the trend has been upward in the Northeast Pacific but downward in the North Indian Ocean. The reason for these changes is not understood, but is thought to be the result of shifts in ocean water temperature, the wind patterns in the upper atmosphere, and, in the case of the North Atlantic, the number and type of storms coming off Africa.
The paragraphs above should be considered with a caveat: Major storms can occur during any month in the hurricane season and sometimes (rarely) in other months. They also can sometimes originate, or travel, outside their usual boundaries. However, no hurricanes arise