Just a quick update on the growing tropical cyclone threat facing the U.S. in coming days and weeks. There are two declared areas of investigation: 92L in the northwestern Caribbean Sea and 93L in the vicinity of the Cape Verde Islands. Obviously the nearest concern is 92L, which will likely impact the Gulf Coast on Saturday August 17. I will argue for a slightly left or west deviation in the track proposed by the GGEM and GFS schemes, if only because all of the model ensemble forecasts place the 500MB weakness (between the Sonoran and Bermudan heat ridges) through Louisiana. I do not see this potential "Erin" as anything more than a tropical storm, though some surprises are possible as the disturbance passes over very warm waters in the Gulf of Mexico, with little shear. Ultimately, the Caribbean Sea disturbance could be a huge rainmaker for much of the Old South. A trough and cold front moving into the Old South will become diffuse, and serve as possibly a steering -and- overrunning mechanism. It seems probable that the low will work only slowly northward toward the Ohio Valley, and in the process dump copious amounts of rainfall in these metro areas: New Orleans LA....Mobile AL/Pensacola FL....Birmingham AL....Huntsville AL....Atlanta GA....Nashville TN....Asheville NC. With time Louisville KY and Huntington/Charleston WV could also have heavy rainfall issues. As for Invest 93L, we will have to wait and see if the massive swirl overcomes the Saharan Air Layer. I think that it will, and within 12 days have a passage through the Greater Antilles and perhaps into the Gulf of Mexico. If the variant members of the numerical models are correct, and the Bermuda High expands a "finger" of ridging into Florida, Georgia and Alabama, we will have to watch for emerging threats to Texas and Louisiana. But that is a long way away, and Invest 92L is the topic of conversation at the weather water cooler for now.
Posted on: Tue, 13 Aug 2013 23:24:21 +0000
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