18 August 2012

Atlantic still active with three storms/disturbances

Gordon is now a hurricane and heading for the Azores, TD7 is now TS Helene, and the disturbance in the far eastern Atlantic continues to get better organized.


 At 09Z today, Gordon was upgraded to a hurricane... the third of the season... based on an improving satellite presentation (most notably, an eye).  The intensity is 65kts with a 988mb central pressure.  It is still zipping off to the east at 16kts, and the anticipated closest approach to the Azores remains Sunday night into Monday morning, likely as a tropical storm.  We could still be watching Gordon into the middle of next week as it heads toward Portugal... though probably not as a tropical cyclone.

Visible satellite image of Hurricane Gordon from 1215Z today, courtesy of NOAA/NESDIS.


At 2130Z yesterday (5:30pm EDT), a special advisory was issued to upgrade former TD7 to TS Helene based on aircraft reconnaissance data.  The storm has been nearly stationary (just a slow northward drift) and sitting off the coast of Mexico near Veracruz.  Fortunately, it is not very well organized and doesn't have a lot of rain coverage over land.  At 12Z today, it was a 35kt storm and just 35 miles southeast of Veracruz and crawling to the northwest at 7kts.  In the image below, the center is shown right on the coast, and the thin white line shows its path over the past few days. I also have radar loops available here (the Altamira site has excellent coverage of the storm, but there's limited precipitation associated with the storm to show up on radar).  Helene is forecast to continue its slow northward drift and gradually weaken over near-coastal Mexico.  The latest position, forecast, and warnings from NHC can be found at http://www.nhc.noaa.gov/storm_graphics/AT07/refresh/AL0712W5_NL+gif/114451W5_NL_sm.gif.

Satellite image of Helene from 1245Z, courtesy of NASA/GSFC.


Finally, on to the disturbance in the far eastern Atlantic.  It is now centered near 12N 28W with an estimated 1008mb surface pressure.

Visible satellite image of AL94 from 1345Z, courtesy of CIRA/RAMMB.

Unfortunately, we still have limited regional model guidance being run on this system due to the other activity closer to land, but all signs point to this becoming a strong hurricane as it heads west toward the Lesser Antilles.  As far as track goes, global deterministic and ensemble models are good at that, and they suggest a steady westward motion, with some members indicating the possibility for some recurvature to the NW in a few days.  An important thing to point out is that models have been trending southward with the track... a couple days ago, the majority were showing recurvature, and now that's more of an outlier solution.

The current satellite image and position, with various 5-day forecast model tracks shown in the multi-colored lines.  The Lesser Antilles is the island chain on the left side of the image, and denote the eastern boundary of the Caribbean Sea.

This system has a good chance of becoming TD9 in the next 1-2 days, and then the next name on the list is Isaac.  To throw in a bit of climatology with it, I centered the storm on its projected location in 24 hours from now (it might be a numbered storm by then), and searched for any storms within 100 miles of that location during the past 160 Augusts to see what storms have historically done.  The tracks are shown below... the vast majority do recurve, but a handful are notorious and include Donna 1960, Frederic 1979, and Dean 2007, so this needs to be taken seriously.

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