Weather patterns

I was reading Jeff Masters’ blog on, and he is the master of understatement:

The death toll on the Philippine island of Mindanao is at least 632, with hundreds still missing, in the wake of extreme flash flooding from Friday’s passage of Tropical Storm Washi. Washi hit Mindanao as a tropical storm with 45 – 55 mph winds, crossing the island in about eighteen hours. Washi was unusually wet, as the storm was able to tap a large stream of tropical moisture extending far to the east (see the University of Wisconsin CIMSS satellite blog for imagery.) Aiding the heavy rains were sea surface temperatures that were nearly 1°C above average off the east coast of Mindanao, one of the top five warmest values on record. The exceptionally warm waters added about 7% more moisture than is usual for this time of year to the atmosphere.

Washi hit a portion of the Philippines that does not see tropical storms and typhoons very often. Mindanao lies between 6°N and 9°N latitude, which is too close to the Equator for the Earth’s spin to provide much help for a tropical storm trying to get spinning. Mindanao is thus hit only about once every twelve years by a significant tropical storm or typhoon. Washi’s rains were not all that unusual for a Philippine tropical storm, with a peak rainfall amount of 7.44″ (189 mm) observed in the city of Hinatuan. However, since the rains fell on regions where the natural forest had been illegally logged or converted to pineapple plantations, the heavy rains were able to run off quickly on the relatively barren soils and create devastating flash floods. Since the storm hit in the middle of the night, and affected an unprepared population that had no flood warning system in place, the death toll was tragically high. Washi is currently a tropical depression near the southern coast of Vietnam, and is dissipating.