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Two Pacific-sized disasters: the Samoan tsunami and Typhoon Ketsana

By: Dr. Jeff Masters, 1:29 PM GMT on September 30, 2009

The Pacific spawned another huge natural disaster yesterday, when a magnitude 8.0 - 8.3 earthquake near Samoa generated a tsunami that devastated portions of American Samoa and neighboring islands. While the ocean surface was only displaced about three inches by the force of the earthquake near its epicenter, the rupture occurred near the 10,000 meter-deep Tonga-Kermadec Trench, along a swath 200 - 300 km long. A column of water miles deep and 200 - 300 km long accelerated downward by the force of gravity (or lifted upward by crustal motion) by three inches represents an massive amount of energy released into the ocean. The quake was able to generate a 1.5-foot tsunami on the Hawaiian island of Oahu 2,700 miles away, and a 0.6-foot tsunami on the Oregon coast, over 5,000 miles away.

Portlight.org is considering adopting an American Samoa family to help out in the wake of this huge disaster. They would like some feedback from their contributors on whether to go ahead with this idea, so stop by the Portlight.org blog to join the discussion.

Typhoon Ketsana
Typhoon Ketsana has finally dissipated, but not before bringing record flooding to Vietnam, two days after creating recording flooding and chaos in the capital of the Philippines, Manila. Ketsana made landfall Tuesday morning in Vietnam between Hue and Da Nang as a Category 2 typhoon with 105 mph winds. The storm dumped up to 20 inches of rain on Vietnam, according to satellite estimates. Some rivers in central Vietnam rose above the record flood heights recorded in an epic 1964 flood. In all, Ketsana has been responsible for 41 deaths in Vietnam and 11 in neighboring Cambodia, with many more missing. At least 350,000 people are homeless in Vietnam, joining the 380,000 left homeless in the Philippines from the storm.

Figure 1. NASA MODIS satellite image of Ketsana approaching Vietnam on Tuesday, September 28, 2009. Image credit: NASA Earth Observatory.

The death toll in the Philippines from Ketsana has stabilized at 246, with another 38 missing. Residents of the islands need to keep a wary eye on Typhoon Parma, which is expected to intensify into a major typhoon and brush the northern Philippine island of Luzon on Saturday and Sunday.

Quietest September in the Atlantic since 1997
Well, it's the end of September, and what is traditionally the busiest month in the Atlantic was unusually quiet. We had only two named storms this September, the first time since 1997 we've had less than three September named storms. There were only 6.75 days in September with a named storm, which ranks as the 4th fewest September named storm days since 1950 (only 1962, 1970, and 1994 had fewer). The Accumulated Cyclone Energy (ACE) index for September ranked as the 6th lowest since 1950. The quiet period is likely to continue for at least another week, as there are no threat areas in the Atlantic to discuss today, and none of the computer models are forecasting tropical storm formation over the next seven days. I'll post my first-half-of-October outlook for the Atlantic tomorrow.

Jeff Masters


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