NHC Statement on October 9th - 10th Storm

[Mr. Rainman]

Bare with me; there's a lengthy quote at the end of this post. On October 10th, Florida saw heavy rains and tropical storm force winds along its eastern coast in association with an invest in that region. A recent review of Facebook posts this evening showed that NHC released an unofficial statement about their thoughts on that system. Final verdict: the system never showed satisfactory signs of being a tropical or subtropical system.

The October cyclone was difficult to classify, consisting of a small area of very strong (~50 kt sustained) winds embedded within a much broader environment of low pressure that was itself producing gale/tropical-storm-force winds, at least early on. The inner system possessed some of the essential characteristics of a tropical storm: it had sustained winds in excess of 34 kt, it had a well-defined center of circulation, it had a warm core, at least in the lower troposphere, and the low center itself did not lie along any frontal boundaries, at least at the time the center moved onshore. In particular, the strength, distribution, and impacts of the winds near the center of this system were indistinguishable from many other small tropical storms.

Other attributes of the system, however, argued against its classification as a tropical storm. The system's convection near the core was intermittent and of short duration, and was considered too transient to satisfy the definition's organized deep convection requirement. The transient nature of the strong inner core circulation itself also cast doubt as to whether it could be considered of synoptic scale. The vertical extent of the cyclonic circulation was limited to below about 12,000 ft, very uncharacteristic of a tropical cyclone of this strength.

We also considered whether the system should be classified as a subtropical cyclone. There were clearly mixed characteristics of extratropical and tropical cyclones present, including the presence nearby of an upper-level cold low, and the large-scale distribution of winds and convection. However, there was enough air mass contrast associated with the system to raise doubts as to whether it was truly non-frontal. The very small radius of maximum winds and occasional convection very near the center also made the system difficult to classify as a subtropical cyclone.

Nature does not always cooperate with the classification systems designed by man. There is a continuum of cyclone types in the real atmosphere, and it is often difficult to place these systems into the small number of bins that meteorologists have created for them. The 9-10 October Florida system is certainly one of these difficult cyclones. NHC’s historical record, however, requires its members to belong to either the “tropical” or “subtropical” bins, and our view in this case is that neither applies. It is simply “something else”.

[Eric]

Whatever it was, it was vile.  I had to walk home from work during the worst of it, and my usual 30-minute walk took almost twice as long.  An umbrella was useless in that rain, so I ended up getting soaked straight through, even with a "waterproof" raincoat.  My feet got so thoroughly soaked that the traces of the skin problems I had are still visible a month and a half later.