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Worldwide,
tropical cyclone activity peaks in late summer when water temperatures
are warmest. However, each particular basin has its own seasonal
patterns. In the North Atlantic, a distinct hurricane season occurs
from June 1 to November 30, sharply peaking from late August through
September. The statistical peak of the North Atlantic hurricane
season is September 10. The Northeast Pacific has a broader period
of activity, but in a similar timeframe to the Atlantic. The Northwest
Pacific sees tropical cyclones year-round, with a minimum in February
and a peak in early September. In the North Indian basin, storms
are most common from April to December, with peaks in May and
November. In the Southern Hemisphere, tropical cyclone activity
begins in late October and ends in May. Southern Hemisphere activity
peaks in mid-February to early March.
Nearly
all tropical cyclones form within 30 degrees of the equator and
87% form within 20 degrees of it. However, because the Coriolis
effect initiates and maintains tropical cyclone rotation, such
cyclones almost never form or move within about 10 degrees of
the equator [1] (where the Coriolis effect is weakest). However,
it is possible for tropical cyclones to form within this boundary
if another source of initial rotation is provided. These conditions
are extremely rare, and such storms are believed to form at a
rate of less than one a century. Most tropical cyclones form in
a worldwide band of thunderstorm activity known as the Intertropical
convergence zone (ITCZ). Worldwide, an average of 80 tropical
cyclones form each year.
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