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(T. F. “Storm” Walsh III)
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Good evening everyone!
First, I am still having a hard time digesting that “Arlene” should have been named. Now, my “colleagues” at the NHC are the “official experts” in the subject. However, I wish to point out some of “my” observations regarding Arlene. In my humble opinion, I believe she should have been kept “sub-tropical” at best. Yes, it had a warm core, however based on the SST’ at the time of designation, the SST was only 19.0C (66F). This is hardly sufficient to perform the true tropical process of maintaining and strengthening a warm core. Pretty much what allowed for a storm to develop, was when the process began, SST’s were 21C (70F). Just barley enough to allow for the baroclinic low to transform to subtropical. In this case, the SST’s were warm enough to aid in warming the “core”, as the atmosphere surrounding the low was colder in relation to the SST’s, as well as colder mid and upper level conditions. This produced a good enough lapse rate to allow for shallow, to moderate convection at best, to develop in two bands just away from the center, which in archived satellite loop imagery waxed and waned. The limited convection that was present, was maintained due to the difference in temperature between the sea and the surrounding atmosphere. Based on the NHC’s own criteria, classification to tropical cyclone status requires organized, “DEEP” convection to be maintained for a minimum of 12 hours, around or near a well defined center of circulation. Review of IR satellite loop imagery may suggest that the moderate convection SW and NE of the center, was brief lived.
I also noted, that during the short life of the storm, winds in the upper levels of the atmosphere remained cyclonic, or counter-clockwise, which meant, there was no outflow channel aloft, to evacuate air in the upper layers, from the rising air coming in at the surface. A tropical storm and hurricane need outflow at the top of the storm, in order to take in more warm air at the surface, and in turn, strengthen. This was not the case with Arlene.
Review of satellite loop imagery revealed (at least to me anyway) that the cloud pattern was not that of a purely tropical system. It resembled more of a storm embedded in a cloud pattern of the baroclinic low that was situated to its west.
Maximum winds were still noted in a band removed from the center of circulation, which is classic of subtropical systems, albeit the distance appeared less than 100 mi, the maximum sustained winds were not located around the center of the system, based on the last available Multiplatform Satellite Surface Wind Analysis.
Anyway, it is what it is, and these are just some of my observations.
A weak area of low pressure is currently making its way NE across the Florida Peninsula from the GOMEX, and is noted in satellite imagery.
Analysis of the Global Models and the NAM Mesoscale model indicate models are in fair agreement of this low becoming better defined, and strengthening, ranging from 1000 mb to 990 mb. This low is progged to move toward the NE during the next 24-30 hours, before merging with a baroclinic low IVO NC/VA. It appears most of the weather will remain on the eastern portion of this system. Models at the moment indicate a small area of 30-35 knot winds in a band on the eastern side of the system, skirting the coast of NC and VA,which will be an onshore wind. Right now, it’s a little too early for me to determine whether or not this may try to acquire sub-tropical characteristics, however once merging with the baroclinic low, some heavy rainfall is possible over localized areas.
GFS AND NAM 72 HOUR RAINFALL TOTALS
Approximately 48 hours into the forecast period, valid 12Z today, the low should begin to move off toward the NNE to NE, and begin to weaken.
I will be monitoring this area, and will try to have an update sometime tomorrow (time still to be determined)
Elsewhere, Tropical Storm formation is not expected.
Have a blessed evening!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS