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August 2012

Watching Helene; 94L Could Threaten the Northern Antilles Next Week

   Posted by Levi at 5:27pm on August 18, 2012

Tropical Storm Helene formed from the remnants of TD 7 in the western Gulf of Mexico yesterday. The mid-level center of this system quickly went inland over Mexico, and this morning the surface center has also crossed the coastline. However, as we have talked about for the last several days, a portion of this system is going to be drawn northward along the coastline in response to a trough digging into the southern U.S., and with the trough being reluctant to pull out quickly, the remnants of Helene could fester near the coast of Mexico over the course of the next several days, possibly redeveloping near the tail-end of the old frontal boundary that will be pushing out over the northern gulf ahead of the upper trough. The models are less supportive of this solution than they were a couple of days ago due to a splitting of Helene’s remnants that is now shown on several models, where a piece gets pulled northeast along the front into Louisiana, and another piece gets left behind off of Mexico, but without enough energy left to redevelop. Some models like the CMC and FIM still show redevelopment, and given the stagnant situation and how Helene has already shown she can develop without model support (they models did not foresee her getting named so soon), she should be monitored over the next 5 days or so.

As Helene dances with death over the next few days, attention will quickly shift away from her and towards Invest 94L in the eastern Atlantic, which is quickly stealing the show in the tropics. This system will be traveling westward and may threaten the northern Antilles islands in 5-6 days as what I think will be a tropical storm. Dry air to the north of the system should keep it from developing quickly over the next few days, and I think it will take until 94L is a couple days away from the islands to earn the name Isaac. As usual in years like this, significant strengthening will likely wait until west of 50W or so, and right now I don’t think the Antilles will be facing a hurricane threat, but a strengthening tropical storm is fairly likely.

While the Antilles may be threatened first, 94L has the potential to impact land farther west. The models today have shifted much farther west than yesterday, showing what I think is a more reasonable track possibility with a recurving storm somewhere between 65W (Bermuda’s longitude) and 80W. Any recurve west of 70W has the potential to impact the U.S. eastern seaboard. The current pattern favors a recurve in this corridor for a strengthening storm coming out of the central Atlantic, and I illustrate this on the ECMWF ensembles in the video.

Overall, we have a very long time to watch 94L, as it is still 5 days or so away from the Antilles islands, and over a week away from any potential impacts on the United States. The pattern favors this system getting uncomfortably close, so we will be monitoring it closely. The Antilles Islands should not be surprised to see a strengthening tropical storm near their doorstep in about 5 days.

We shall see what happens!