# What is a tropical storm?

You can think of a tropical storm as a less-intense hurricane (you can also call a hurricane a more intense tropical storm). If wind speeds are between 38 and 74 miles (61 and 119 kilometers) per hour, then it is considered a tropical storm and not a hurricane.

# What is a tropical depression?

A tropical depression consists of a line of organized storms with wind speeds Tropical depressions have the potential to below 38 miles (61 kilometers) per hour. become tropical storms or hurricanes.

A space image of 2005's Hurricane Katrina shows a well-defined, powerful storm system heading for the Gulf Coast. (WA5A)

# What is the Coriolis effect?

Named after French mathematician scientist Gustave Coriolis (1792-1843), who first explained it in 1835, the Coriolis effect refers to the way objects appear to move in a curving or circular pattern when observed from a point of view position that is rotating. Imagine yourself standing next to a playground carousel. Two of your friends are riding on opposite sides of the carousel as it spins around. One friend holds a ball and tries to roll it to the person on the other side, but as he does so, the ball seems to veer to one side and roll off the carousel. To your point of view (as you stand off to the side), however, the ball rolled in a straight line, but it did not reach your other friend because as the ball moved across the carousel moved beneath it and the intended receiver was no longer in the original position.

Now imagine the Earth as it spins on its access. Above the Earth, suspended in the atmosphere, is a forming hurricane. The air around the hurricane is moving toward the eye, which is where the lowest air pressure is. However, as the air moves toward the eye, it is deflected to the right (in the Northern Hemisphere) by the

Does the Coriolis effect make the water in my toilet, sink, and bathtub swirl clockwise?

No, the Coriolis effect has very little effect on such small bodies of water. The flow down the drain is mostly a function of the shape of the container. Interestingly, if your body were completely symmetrical (and no one's is) and neither leg were longer and you were walking on perfectly flat land then you might start veering due to the Coriolis effect.

Earth's spin, or to the left (in the Southern Hemisphere). This causes the hurricane clouds to rotate counterclockwise in the North and clockwise in the South.

# What part of a hurricane is most damaging?

Floods caused by hurricane storm surges are the most destructive element. The low-pressure center of a hurricane causes a mound of water to rise above the surrounding water. This hill of water is pushed by the hurricane's fierce winds and low pressure onto the land, where it floods coastal communities, causing significant damage. Hurricanes sometimes spark tornadoes that contribute to the devastation.

# How fast do hurricanes travel?

A typical hurricane will travel across the ocean at a speed of about 250 miles (400 kilometers) per day, or about 10 to 15 miles (16 to 24 kilometers) per hour. They have been known, though, to advance at speeds as fast as 60 miles (96.5 kilometers) per hour, which was the case during the New England hurricane of 1938.

# What is a storm surge?

Not to be confused with a tsunami, a storm surge is a sudden upwelling of ocean water caused by winds and pressure changes affecting the water's surface. Hurricanes generate large waves—swells—that radiate outwards in all directions as they travel over the ocean. The swells, which can move toward the shoreline about three or four times faster than the actual storm, arrive on land before hurricanes strike. Before advanced weather systems and the use of satellites, these swells warned people that a hurricane was approaching. The swells become storm surges by the time the main storm arrives, raising water levels as much as 25 feet (7.5 meters) and causing massive coastal flooding. By some estimates, the storm surge resulting from 2005's Hurricane Katrina was 28 feet (8.5 meters).