2024年4月7日发(作者：)

英文阅读：Typhoon（台风）

What is a Typhoon?

A typhoon is a large and powerful tropical cyclone, a low pressure area rotating

counterclockwise and containing rising warm air that forms over warm water in the

Western Pacific Ocean. Less powerful tropical cyclones are called Tropical

Depressions and Tropical Storms. A typhoon is called a hurricane in the Atlantic

Ocean, and a cyclone in the Indian Ocean. In this web page the terms typhoon and

hurricane are used interchangeably. Typhoons can inflict terrible damage due to

thunderstorms, violent winds, torrential rain and accompanying flooding and

landslides, incredible waves, and extremely high tides associated with tidal surges.

Hurricane-force winds can reach out as little as 25 miles from the center of a small

hurricane and as far as 150 miles in a large hurricane. Tropical storm-force winds can

extend as far as 300 miles from the center of a large hurricane. These are very

dangerous storms.

Typhoons in Japan

Typhoons can strike Japan in any month, but typhoon season ranges from May to

November, with peak danger in August and September. Typhoons are rare from

December to April. An average of about 28 typhoons form each year in the Western

Pacific, and an average of approximately 3 of these storms pass across Japan. The

number of storms to hit Japan can vary considerably, in 2004, 10 typhoons hit the

Japan mainland. Typhoons are formed in the tropical areas of the Western Pacific

Ocean and typically in August and September travel north toward Japan along the rim

of a high pressure area in the middle of the Pacific Ocean. Typhoons can strike

anywhere in Japan, but usually strike on the Pacific Ocean side, from the Kanto Plain

to the Ryukyu Islands.

Typhoon Strength and Speed

In the United States, hurricanes are tracked by the National Hurricane Center,

part of the National Weather Service, which is itself part of the National Oceanic and

Atmospheric Administration (NOAA). However, in the Pacific Ocean area, the U.S.

Navy's Joint Typhoon Warning Center, based in Hawaii, provides typhoon tracking

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services. There are very slight differences in the terminology used by these two

services, and the number assigned to the typhoon also varies. In Japan, the Japan

Meteorological Agency (JMA) is responsible for typhoon tracking. There are certain

differences in the ways typhoons are measured in Japan and the United States, in

particular how the storms' strength and speed are measured.

First, in the United States, these storms' sustained wind speeds are measured in

statute miles per hour, while in Japan the typhoon's speed is measured in kilometers

per hour and the sustained winds within the storm are measured in meters per second.

The conversion is: 1 knot (kt) = 1.15 mile per hour (mph) = 1.85 kilometers per hour

(km/h) = 0.514 meters per second (m/s).

Second, the time period over which maximum sustained wind speed is measured

is different: in the United States the wind speed is measured over a one-minute period,

in Japan it is measured over a ten-minute period. In practice, this means that the same

storm will show lower wind speeds in Japan and higher wind speeds in the United

States. Put differently, to an American this means that a typhoon in Japan with winds

of a given speed will be more destructive than would be expected for a storm of that

size. Note that gusts of wind are not factored into the sustained wind speed, and these

gusts' speeds can be 20% or even higher than the speed of the sustained winds.

Because of these differences, we have placed each system on a separate chart to

reduce confusion. We recommend that viewers refer to both charts. The chart labeled

United States System of Hurricane Classification is an amalgamation of the National

Hurricane Center, Joint Typhoon Warning Center, and other classification systems.

Finally, Japan also classifies the scale of the typhoon, that is the radius of the area in

which the wind speed is over 15 meters per second. The United States does not use

this classification system. The Joint Typhoon Warning center updates its information

every six hours, while the Japan Meteorological Agency updates its information every

three hours, and every hour upon a storm's approach to Japan.

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