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 , 3:30 PM GMT on December 13, 2012
The Southern Hemisphere tropical cyclone season is beginning to heat up. Category 2 Tropical Cyclone Evan is pounding Samoa and American Samoa with heavy rains and high winds, after making landfall earlier today on the north shore of Samoa near the capital of Apia. At landfall, Evan had a small 10-mile diameter eye and top winds of 90 mph, but has since intensified to 105 mph winds. Media reports indicate that Evan has killed two, and brought a 12 - 15' storm surge, heavy rains, and severe damage to the island nation. Satellite loops show a well-organized storm with a tiny 7-mile diameter eye. Evan has plenty of intense heavy thunderstorm activity near its core, solid upper-level outflow, and is in an area with weak steering currents. Evan is expected to meander over Samoa until about 18 UTC on Friday, when a ridge of high pressure will build in and force the cyclone to the west. The storm will be in a region with light wind shear and very warm ocean waters that extend to great depth, and could intensify into a Category 3 or 4 cyclone by this weekend. On Sunday, when the ECMWF model predicts that Evan will be near Fiji, the storm will encounter increasing wind shear and should weaken.
Figure 1. True-color MODIS satellite image of Tropical Cyclone Evan over Samoa at 01:05 UTC December 13, 2012. At the time, Evan was a Category 1 storm with 90 mph winds. Image credit: NASA.
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