What's a Typhoon, Anyway?

A powerful typhoon that will hit the Philippines on Friday has triggered mass evacuations from coastal and low-lying areas as the nation's islands brace for the storm's surge.

Super typhoon Haiyan, or Yolanda, has strengthened into one of the most powerful tropical storms ever recorded, with sustained 190-mile-per-hour (306-kilometer-per-hour) winds and gusts as high as 230 miles-per-hour (370 kilometers-per-hour).

The Category 5 typhoon is expected to hit the Philippines at full strength.

"The deadliest threat from Philippine typhoons is usually heavy rains, since the islands are very mountainous, leading to very high rainfall amounts capable of causing dangerous flash floods and mudslides," says meteorologist Jeff Masters on his WunderBlog website.

How do typhoons differ from hurricanes or cyclones? It turns out they don’t, except for their location.

Rotating Sea Storms

Hurricanes, cyclones, and typhoons are all the same weather phenomenon. Scientists just call these storms different things depending on where they occur:

In the Atlantic and northern Pacific, the storms are called hurricanes, after the Caribbean god of evil, named Hurrican.

In the northwestern Pacific, the same powerful storms are called typhoons. In the southeastern Indian Ocean and southwestern Pacific, they are called severe tropical cyclones.

In the northern Indian Ocean, they're called severe cyclonic storms. In the southwestern Indian Ocean, they're just tropical cyclones.

To be classified as a hurricane, typhoon, or cyclone, a storm must reach wind speeds of at least 74 miles per hour (119 kilometers per hour).

If a hurricane's winds reach speeds of 111 miles per hour (179 kilometers per hour), it is upgraded to an intense hurricane.

If a typhoon hits 150 miles per hour (241 kilometers per hour)—as Haiyan has—then it becomes a super typhoon.

Different Seasons

While the Atlantic hurricane season runs from June 1 through November 30, the typhoon and cyclone seasons follow slightly different patterns.

In the northeastern Pacific, the official season runs from May 15 to November 30. In the northwestern Pacific, typhoons are most common from late June through December. And the northern Indian Ocean sees cyclones from April to December.

Whatever you call them, these monster storms are powerful natural events with the capacity to wreak some serious havoc.

According to NOAA's National Hurricane Center, the average hurricane eye—the still center where pressure is lowest and air temperature is highest—stretches 30 miles (48 kilometers) across, with some growing as large as 120 miles (200 kilometers) wide.

The strongest storms, equivalent to Category 5 on the Saffir-Simpson scale, have sustained winds that exceed 155 miles per hour (250 kilometers per hour).

With the aid of satellites and computer models, such storms can be predicted several days in advance and are relatively easy to track. But as Hurricane Sandy showed recently, predicting the path that a hurricane, typhoon, or cyclone will take after it's formed is still tricky.

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