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Susan Kieffer can be contacted at s1kieffer at gmail.com

Sunday, September 16, 2012

Typhoon Sanba--and what is a "super typhoon"?

Sanba--NOAA image
Typhoon Sanba is churning away in the Phillippine Sea, having hit Okinawa and moving north toward South Korea and, eventually, China.  Sanba can't be aware of it, but it's got two friends in the eastern Pacific--Kristy and Lane-- and one in the Atlantic--Nadine--that NOAA is keeping track of. Sanba is going to encounter warm water for the first half of its trip between Okinawa and South Korea, but cooler water on the second half. That should at least be some help in moderating its intensity before it strikes South Korea, but it is still expected to be severe. China is already calling on residents to prepare for the storm. The possibility of landslides looms large there.

Sanba has been called (briefly) a super-typhoon. In a previous post, I discussed super-typhoon Tracy, which was so large that it would have covered the whole western half of the U.S. Sanba, like Tracy, is a huge storm.

Projected trajectory for Sanba. NOAA image.
However, sheer size doesn't make a super-typhoon. To be officially a super-typhoon, a cyclonic (rotating) storm must have winds that reach "maximum sustained 1-minute surface winds" of at least 150 miles per hour (65 m/s, 130 knots). It is the equivalent of a strong category 4, or category 5, hurricane in the Atlantic on the Saffir-Simpson scale, or a category 5 "severe tropical cyclone" in the Australian basin. As an example, super-typhoon Pongsona that hit Guam in 2002 had gusts to 173 mph, and sustained winds of 144 mph. This storm also was huge, with an eye almost 40 miles in diameter.

Sanba formed from a tropical depression on September 11, and fueled by warm water, had maximum sustained winds of 175 mph, with sustained winds to about 200 mph (information from earthsky.org here.) It made landfall in northeastern Okinawa early Sunday morning at 6:30 a.m. Okinawa time (5:30 p.m. east coast time in the US). The eye was nearly half the islands length in diameter. At this time, the maximum sustained winds were down to 120 mph, and gusts were measured up to 149 mph. (The Joint Typhoon Warning Center is the U.S. miliary agency responsible for issuing tropical storm warnings in the Pacific.)

Here are other posts on typhoons:

Megi: Taiwan
Tracy: Australia, Queensland
Irene: U.S. east coast
Yasi: Australia

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