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By: NCHurricane2009 , 4:45 AM GMT on May 21, 2012
...MAY 21 2012...
Just after stroke of midnight...Alberto shows a definite and more offshore course. I am writing this special update to change my forecast from discussion #14 accordingly.
It has been interesting to watch Alberto move in relation to an adjacent upper low...which first was west of Alberto (over Georgia) in discussion #13...south of Alberto in discussion #14...and now northeast of Alberto in this special update (#14A). Recently...Alberto's track has shifted from SW...to south...to now SE. Putting Alberto's motion together with the upper low's motion...both seem to be cyclonically orbiting about each other in a fujiwhara-like interaction (normally fujiwhara interactions are associated with two tropical cyclones cyclonically orbiting each other).
I now expect Alberto to continue cyclonically orbiting about the adjacent upper low...accelerating to the SE...E...then NE. The incoming frontal upper trough from the west will then absorb this upper low and accelerate Alberto NE for the remainder of its lifespan. My updated forecast track (below) is just to the right of the NHC's...accounting for the very recent acceleration to the SE toward 30N latitude. In terms of how far north Alberto will get...I expect it to be behind in timing compared to the NHC's forecast track due to the recent SE motion. So I took all 8 O'clock positions and made them around 11 O'clock.
Intensity-wise...Alberto keeps on firing small bursts of T-storms near the center...perhaps due to instability caused by the temp difference between the warm ocean surface and adjacent cold core upper low. So I keep it at 40 mph (minimal tropical storm) for the first few forecast points...then I weaken it to 35 mph (tropical depression or remnant low) when I think southwesterly vertical shear (from the incoming frontal upper trough) and cooler waters will start killing off Alberto.
This more offshore forecast (compared to the close-shore forecast in discussion #14) means that the threat of direct impacts (i.e. gusty showers) no longer applies to all land areas. The narrow blue-swath of gusty shower impacts in the graphic below is based on the current small diameter of convective T-storms near the center...and then I lean this swath toward the right-of-center later in the forecast as gusty winds are always to the right in an accelerating cyclone.
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