Typhoon Development

Typhoons are intense tropical cyclones that occur in the western part of the North Pacific Ocean known as the northwest Pacific Basin. Tropical cyclones develop throughout the year in the northwest Pacific Basin with peak months in August through October.

The Edge of Typhoon Halong from the International Space Station
by Alexander Gerst (ESA/NASA), July 31, 2014

A third of all tropical storms occur in the northwest Pacific Basin.

Tropical storm intensity is categorized by sustained wind speed ranges by the Regional Specialized Meteorological Center. Typhoons have wind speeds ranging from 73 to 97 miles per hour.

Three tropical cyclones
over the Pacific Ocean

Tropical Cyclone Intensity Scale

Category	Sustained Winds
Typhoon	64–84 knots 73–97 miles/h
Severe Tropical Storm	48–63 knots 55–73 miles/h
Tropical Storm	34–47 knots 39–55 miles/h
Tropical Depression	≤ 33 knots ≤ 38 miles/h

Conditions for typhoon development are:

• Warm ocean surface temperatures;
• Atmospheric instability;
• High humidity in the lower to middle level of the troposphere;
• Sufficient Coriolis force to develop a low pressure center;
• Pre-existing low level disturbance; and
• Low vertical wind shear.

The Japanese characters 台風 are pronounced taifū which might be the derivation of the word typhoon. It might also originate from:

• the Cantonese t'ai fung meaning great wind;
• the Arabic tufan meaning smoke; or
• the Greek typhon meaning monster.

Greek philosopher and scientist Aristotle used the word typhon to mean wind-containing cloud.

REFERENCES

• How do tropical cyclones form? NOAA Hurricane Research Division.
• Typhoon, Meteorology Glossary, American Meteorological Society.
• Typhoon, Wikipedia.