08 September 2011

Katia turns north, Maria struggles, and Nate strengthens

Hurricane Katia strengthened slightly to 80kts as of 15Z today, and did indeed pass over Buoy 41048 as expected -- the center of the eye was actually 34 miles west of the buoy at closest approach at 09Z.  It has also completed its turn to the north, and over the next few days will turn northeast and out into the north-central Atlantic graveyard.  However, it's only a graveyard for tropical cyclones... it will still be an extremely potent and dangerous extratropical cyclone as it heads for the UK early next week. 

Peak observations from the [un]lucky buoy include a 976mb pressure, 40-foot significant wave height, 68kt sustained winds, and 93kt wind gusts.  The SST dropped from its pre-storm value of 28.4C to a low of 25.1C!

Maria is still a 40kt tropical storm, but looks quite anemic this morning... a sign that shear and dry air are nudging their way into the vortex.

The plot below is the initial condition from HWRF's 06Z run... it's an along-shear cross-section of wind speed and relative humidity.  You can clearly see the asymmetry in the wind field (shaded), as well as the low RH values (contours) being forced into the system by the strong shear.  The official forecast brings Maria over the central Bahamas in 5 days as a strong tropical storm.  Given this track, the southeast and east coast of the US should be very alert... this is nearly a copy of Irene's track.

Tropical Storm Nate is at 45kts, and still virtually stationary.  It's forecast to slowly intensify to a hurricane on Saturday as it begins to crawl to the northwest toward the US/Mexico border next week.  You can view full-resolution visible images of Nate at http://rammb.cira.colostate.edu/ramsdis/online/loop_640.asp?product=tropical_ge_1km_center_relative_vis_floater

Please visit my tropical Atlantic headquarters.

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