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Is the recent typhoon activity in the Western Pacific unusual or not?

Question submitted by Ross McKinnon
(Hainan, China)

First off - let me copy the entire e-mail that I got from Ross:
"I live on the Island of Hainan in the South China Sea, and have been here for the past seven years from my former home on Pender Is. BC. We are now just waiting for our 6th typhoon of the year, all in the past 8 weeks. This is 6 more than has ever occurred here before, so what is going on?"

Great question! Here's what I have discovered:

To date we have seen eight tropical cyclone, five of which became typhoons, two reaching Super Typhoon status, the strongest classification of tropical cyclones in the Western Pacific. But when we look at the numbers, 2009 has actually been slightly below average. So far we have seen 19 tropical storms in the Western Pacific, which is slightly behind the pace needed to reach the yearly average of 27. Despite the fact that 2009 has been below average for the season, the past month has been remarkable, with five of the eight storms making direct landfall in Asia.

What is behind this recent uptick in activity and why are all the storms seemingly coming at once, and late in the season?

The answer may be El Nino, which refers to a periodic change in the atmosphere and ocean in the Pacific. During El Nino, the waters in the central and eastern Pacific are warmer than normal, and the effects on global weather can be drastic and far-reaching.

According to forecasters in China, we see more cyclones later in the season during El Nino years in the Western Pacific, and they tend to form farther east. With the warmer sea surface temperatures during an El Nino event, this would allow these storms more time over open water to grow into large and powerful typhoons. In fact, we tend to see more "Super Typhoons" during El Nino years, and this is true again this year, as Choi-Wan and Melor both reached Super Typhoon status.

El Nino also is a likely culprit for the inactivity in the North Atlantic, since El Nino can cause more wind shear in the upper atmosphere, a condition that limits the ability of Tropical Cyclones to survive.

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