Steve Baier, age 13, of Williamsport, Pennsylvania, for his question:
What causes hurricanes to occur in certain seasons?
Every year, about ten hurricanes are born above the Atlantic near the West Indies. They move westward and some of them turn north, ripping paths of destruction through New England. Luckily, the season for these East Coast hurricanes lasts only six months, from June through November.
Hurricanes breed only in certain regions above tropical oceans. And each breeding ground has a limited season. The world's worst hurricane hatchery is in the mid Pacific, between the Philippines and the Marshall Islands. From here, the wild storms rage westward to touch the China coast, then north towards Japan. There is another hatchery off western Mexico and another in the Indian Ocean. The southern hemisphere also has its share. There is a hurricane hatchery off northern Australia, another in the southern Indian Ocean and another in the South Pacific Ocean.
There are eight of these regions. Our damaging hurricanes are born in the Atlantic, near the West Indies or as far away as the bulging coast of Africa. Sometimes they take devastating paths through the Gulf of Mexico and Central America. Sometimes they turn north and smash through New England. They are born during the summer season, when the sun is north of the equator. In winter, when the sun moves south of the equator, the various hurricane hatcheries in the Southern Hemisphere have their season.
Most meteorologists suspect that the hurricane seasons are linked to the seasonal migrations of the sun. Certainly it is one of the factors governing hurricane seasons but at present no one can explain all the details. The mid day sun is directly over head only in the tropics. As it moves, it causes changes in the pattern of planetary winds.
The northeast and southeast trades blow toward the equator and lose themselves in a wide belt of calm, rising air. This equatorial calm is the ITCZ, short for "Intertropical Convergence Zone." Sometimes the trades breeze through the ITCZ. The northeast and southeast winds then tangle and spin around in a whirling eddy. Such a windy pocket can start the spiraling motion of a howling hurricane.
In summer, the ITCZ is north of the equator and eddies of converging trade wands occur in the Northern Hemisphere. So does the season of hurricanes. In winter, the sun moves south of the equator and the ITCZ moves with it. So do the eddies of tangling trade winds and the season of hurricanes.
At present, we cannot explain the causes of hurricanes and their seasons in exact detail. Certainly the massive storms need the hot, moist air above tropical seas. However, they never form directly above the equator where a belt of this calm, light air always ' exists. Hurricanes tend to follow the seasonal moves of the sun north and south of the equator. With it moves the ITCZ where opposing trade winds tend to tangle. These breezy tangles are a factor and perhaps a major cause of hurricane seasons.