In effect that high creates a bubble of pressure that sits in the middle of the Atlantic. The hurricane can't move into the bubble, so it goes around it. Some hurricanes stay largely at sea, sliding up between the high pressure zone and the east coast. Others swing wide and plow right into North and Central America.

Hurricane Katrina did more than $81 million in damage and killed 1,836 people.

The longer a hurricane dawdles in warm tropical waters, the bigger it gets. That means the winds will continue to increase and create big waves. These waves tend to move faster than the winds; as they move away from the storm area, they smooth out and stretch into long swells. These swells can cover 1,000 miles in a day, whereas a hurricane usually travels only about 330 miles. That means shore-dwellers often get a two-day warning that something ominous is headed in.

Because winds spiral counterclockwise, and a hurricane moves forward, the storms right side packs its most powerful punch. This is known as the hurricane's "dangerous semicircle." Meanwhile, winds on the left side of the storm are reduced by the speed of its advance, producing the so-called "navigable semicircle." That term sounds benign, but it was Katrina's navigable semicircle that plowed through New Orleans, permanently disfiguring one of the nation's most historic cities.

Hurricanes are born on the east side of the North Atlantic and eventually die on the west side. If a hurricane stays out to sea, cold water from the north will eventually kill it. Similarly, as a hurricane crosses onto land and moves inland, it loses its source of energy and begins to decay. In time the storm's winds slowly decrease. But even rainfall from a dying hurricane can be prodigious–enough to wash the topsoil off mountains and turn them into mud slides. While people living on the coast suffer the most wind, it's those living inland who tend to face danger from floods.

Similar storms in the Pacific are known as typhoons.