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Posted at 11:48 AM ET, 09/06/2012

Michael: first major hurricane in super active Atlantic season; Leslie drifts towards Bermuda


A close-up view of hurricane Michael. (NOAA)
Michael unexpectedly exploded last night, becoming the 7th hurricane and the first major, category 3 storm of the Atlantic 2012 season. The only seasons on record that reached 7 hurricanes sooner were 1886 and 1893.

To the west, Leslie remains a minimal hurricane as it heads towards Bermuda. Meanwhile, the “ghost of Isaac” has not gotten any better organized in the northern Gulf of Mexico. It only has a small window of opportunity to develop before conditions become too hostile for it.

Michael

This intensity of this storm is a huge surprise. “Born” in a non-traditional way from an upper-level low (as opposed to an easterly wave) four days ago, it was never expected to become anything more than a strong tropical storm. But, to keep forecasters and modelers humble, it rapidly intensified to a category 3 hurricane packing 115 mph sustained winds at 5 am this morning... making it the strongest storm of the season so far.


Infrared satellite images of Michael 24 hours apart. Full satellite loop spanning these times is a also available. (CIRA/RAMMB)
When it first formed as a tropical depression (TD13), the National Hurricane Center predicted to be a 30 mph remnant low at this time. The first advisory written on it as Tropical Storm Michael had a forecast intensity of 40 mph valid this morning. Models didn’t do much better.

The reality: between 5 a.m. on Wednesday and 5 a.m. today, the pressure fell 1.18” (40 mb) and the maximum sustained winds increased by 63 mph (55 kts). Truly a remarkable case of rapid intensification!

The two infrared satellite images shown here are from those two benchmark times – 5 a.m. yesterday (top) and 5 a.m. today (bottom). Some key features to look for in a mature intense hurricane are a clear eye (the gray hole in the middle), a vigorous eyewall surrounding the eye (the ring of green indicating cold cloud tops and violent thunderstorms), and symmetric outflow (the wispy white and lighter blue colors).

Hurricane Michael is located about 980 miles west-southwest of the Azores and heading northeast at 7 mph. Some additional strengthening is possible today, but it has likely peaked and will begin to weaken as it heads over colder and colder waters in the coming days.

Leslie


Satellite image of Leslie with past track, current location, and forecast track with cone of uncertainty overlaid. Bermuda is the island in the upper left corner of the image. (UW/CIMSS)
Hurricane Leslie remains a 75 mph category 1 hurricane, and is heading north towardd Bermuda. The latest model guidance and official forecast have the center of the storm passing about 120 miles east of the island, putting them on the “weak” side of the storm. The closest approach is expected on Sunday as a Category 1 or 2 hurricane.

I have a long radar loop from Bermuda running to help track the center and the outer structure as it passes the tiny island. New frames are continuously being added, so check back later too. Newfoundland continues to be in the crosshairs for a potent encounter toward the end of next week.

Ghost of Isaac

The disturbance that entered the northern Gulf of Mexico yesterday (“ghost of Isaac”) has struggled with strong vertical shear, and a general lack of organization.

It’s currently centered near the Mississippi delta in southeasternern Louisiana, and drifting south. Models continue to agree that this system will sit in place for another day or so, then start moving east toward Florida... most likely as nothing more than a lot of rain, but perhaps a tropical depression. Nothing to be concerned about, but the Florida panhandle and northern peninsula should be prepared for the possibility of some flash flooding in the Sunday-Tuesday timeframe.

Atlantic hurricane season 2012 stats

With the surge of higher-end activity provided by Michael, the ACE (Accumulated Cyclone Energy) takes bigger strides each day (see previous post for description of ACE). If you recall, ACE uses the square of wind speeds, so squaring a big number racks up points much faster than squaring smaller numbers! As of 8am this morning, the seasonal ACE stands at 61, or 143% of an average season on this date (using the 1981-2010 base). And again, keep in mind that we haven’t even reached the climatological peak of the season yet.

* Brian McNoldy is a senior researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science.

By Brian McNoldy  |  11:48 AM ET, 09/06/2012

Categories:  Latest, Tropical Weather

 
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