Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 7:03 PM GMT on December 11, 2006
The Philippine Islands continue to assess the damage from Typhoon Utor (called Seniang in the Philippines). Utor (the Marshallese word for a squall line) hit the eastern Samar province Saturday as a Category 1 typhoon on Saturday, then intensified to a Category 3 typhoon as it passed through the islands, striking Mindoro Island as a Category 3 storm before passing out into the South China Sea. Thankfully, Utor moved at a much quicker speed through the islands than devastating Super Typhoon Durian did at the end of November, and thus dropped only about half the amount of rain. The death toll from Utor is 6, with 19 missing. Most of the missing are fisherman that may yet be found. Utor did not trigger major mudslides and flash flooding like Durian did, and the storm is expected to die in the South China Sea and not create significant problems for any other nations. A list of the typhoons to hit the Philippines so far this year, and their strength at landfall:
Chanchu (May) Cat 2
Xangsane (Sept) Cat 4
Cimaron (Oct) Cat 5
Chebi (Nov) Cat 3
Durian (Nov) Cat 4
Utor (Dec) Cat 3
Utor was unusual in that it intensified significantly from a Category 1 storm with 75 mph winds to a Category 3 storm with 115 mph winds while it passed through the islands with much of its circulation over land. Normally, the friction created when a typhoon's winds pass over land will weaken the storm. In Utor's case, however, the inner core of the storm remained over warm (29 C) waters, and it may be that the funneling effect of the low-level wind flow through the spaces between the islands acted to accelerate the winds flowing into the eyewall. These faster winds near the core brought in more water vapor to fuel the storm and generated enhanced updrafts in the eyewall, allowing the typhoon to intensify despite the frictional drag of land on the rest of the storm. It is also possible that the relatively protected waters between the islands allowed the large waves kicked up by the storm to die down, reducing the amount of frictional drag on the winds and thus aiding intensification. A detailed computer simulation of the air-sea interaction of Utor is needed to figure out what happened, though.
Figure 1. Satellite image of Typhoon Utor from NOAA.
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