IMHO, yes!
This blog will provide an explanation of my reasoning. For additional perspective, TWC's Dr. Rick Knabb and Bryan Norcross discuss the event in an on-camera segment here.
There's an infinite variety of weather systems in the tropical-subtropical-extratropical continuum, the one which hit Florida over the weekend being another fascinating example.
A couple of particularly bizarre & wild ones have occurred in recent years: what I dubbed the "MCV-icane" in southern Illinois in May 2009, and the regeneration of what had been Tropical Storm Erin in 2007.
The system this weekend paradoxically had characteristics of both a large non-tropical nor'easter and, embedded within it, a small tropical cyclone. In that sense, although there were significant differences in strength, location, and origin, Sunday evening's odd bird was at least of a similar species to the small unnamed hurricane that developed within the larger Perfect Storm in 1991.
So in the big picture the current system has been a hybrid, but what about the potent component that hit Florida Sunday night, the feature that I'm suggesting was a tropical storm even though officially it wasn't? What's up with that?
It's perfectly okay for meteorologists to have honest, legitimate, amicable professional differences of opinion on the analysis of meteorological aspects of a weather system. The tricky part with tropical and subtropical cyclones in this part of the world is that only the National Hurricane Center can officially classify them as such and name them.
For example, I could identify a thunderstorm's radar signature and publicly say it's a supercell, and as long as it's based on a sound meteorological analysis, there's no issue. Not so simple, however, if I say something's a tropical storm when it officially wasn't. But that's what I'm going to do anyway. :)
To be clear, I'm not criticizing the National Hurricane Center for not calling it a tropical storm Sunday evening. In addition to the squirrelly, short-fused meteorological nature of that weather system, there are many operational considerations in terms of what's issued to the public, the coordination of that between the National Hurricane Center and local National Weather Service offices, etc. In this case, there were plenty of advisories, watches and warnings issued in the days leading up to the overall event, and then short-term ones issued specifically for what spun up offshore Sunday evening.
Rather, this is in the spirit of a post-storm analysis, learning about that infinite variety of curve balls that the atmosphere can throw. NHC does the same, sometimes classifying things differently in the postseason than in real-time, such as when they "posthumously" identified an unnamed subtropical storm in 2005.
I've blogged about official tropical-or-not classifications of cyclones in the U.S. in the past, when I wrote that the aforementioned Erin should have been classified as a tropical storm when it reorganized and reintensified over Oklahoma, and raising a similar issue about the remnant circulation of Olga when it reached Florida in December 2007.
This is an academic exercise of meteorological semantics, but it also has relevance for what it means for people affected, as winds were much stronger on a portion of the Florida coast Sunday evening than they otherwise would have been.
During the day Sunday, there was a feature just north of Grand Bahama Island and offshore of the east coast of Florida, which was trying to become a surface low pressure center -- a "closed" circulation -- within the larger overall system that had been pummeling the state with heavy rain, high surf, and gusty winds as a result of persistent, long, moist onshore fetch associated with the pressure gradient between a strong high pressure system to the north and relative low pressure to the south.
Early Sunday evening, I was about to relax, put on the headphones and go for a nice long walk in the neighborhood when I thought I ought to check on the latest radar imagery. I saw what's below! Whoa! That was one of those meteorological "Houston, do we have a problem?" moments.
[Click on image for larger version.]
Not only was there now a very well-defined, tight circulation (indicated by the red and green colors which show winds blowing in opposite directions in close juxtaposition) over the very warm Gulf Stream, but the velocities measured by radar were upwards of 80 mph, at a low altitude of approximately 2400'. Even though winds certainly weren't sustained that strong down at the Earth's surface, this suggested both that it wasn't just a circulation way up in the atmosphere, and that very strong winds could be transferred down to the surface in gusts.
A little while later, not only was the radar presentation (image below) of the "reflectivity" i.e. precipitation more circular, there was a signature of a partial eyewall. Velocity images at the time still showed a tight circulation with strongest winds right around the center. This is not only not typical of an extratropical (non-tropical) cyclone, it doesn't fit with the latest official definition of a subtropical cyclone either. Furthermore, it was not collocated with the cold mid and upper level low.
But what about actual surface observations?
Welll ... I checked the surface pressure plot of the buoy which is just offshore of Cape Canaveral, and saw this!
That plummeting surface pressure provided sufficient evidence that there was a solid manifestation down to the surface of what radar was observing above.
Here, after the fact, are two graphs which further support that a cyclone characteristic of a tropical storm made landfall last night.
This is the pressure trace at Trident Pier near Cape Canaveral. The center of circulation came very close. Notice how sharply the pressure fell and then rose, typical of the center of a tropical cyclone passing overhead. Also, the pressure reached 999.5 millibars, typical of one of storm (rather than depression or hurricane) strength.
And here is a graph of the sustained wind speed. It's a little harder to decipher so I've added circles for assistance. The red one indicates a sustained wind speed of tropical storm force. Where the line is circled in light blue shows that just a very short time later the wind had gone to nearly calm, as the eye-like portion of the storm came overhead. Then the wind quickly increased again (orange). Also, the wind shifted to the opposite direction, indicative of a closed surface circulation, as were other surface observations.
Stephen Sponsler, a meteorologist who lives right where the circulation came onshore, has posted some interesting observations here and here on Facebook .
The one piece of information that is unavailable is the detail of the temperature structure in the heart of the circulation. By definition, tropical cyclones are "warm-core," which is as it sounds: the temperature in the vertical core of the cyclone extending up through the atmosphere is higher than in the air surrounding it. Absent aircraft recon, or a "radiosonde" balloon having been released right as the tiny center passed overhead, we can't be certain of this aspect.
But what's known as a "cyclone phase" analysis indicated the system was warm-core [see addendum below for more info], and the preponderance of other available evidence suggests that this cyclone at the time it approached the coast and made landfall was more of a tropical cyclone by nature than a subtropical or non-tropical one. It was very short-lived and small in size, but there have been other very small ones, such as Lorenzo in 2007, and a number of very short-lived tropical cyclones. Likewise, while this storm had a sheared and asymmetric appearance on satellite imagery, there have been many tropical cyclones with asymmetry and upper-level wind shear.
Whatever it's called, there's one thing we can all agree on! The result:
Stu's TWC Facebook page
Follow Stu on Twitter
[Monday evening addendum: Although that "cyclone phase" diagram to which I linked had the cyclone as being solidly warm-core, it also showed that warm core as being relatively shallow. Analyses from other models such as this one presented a warm core of moderate depth. A shallow to moderate, rather than deep, warm core can be an indication of a cyclone which is more subtropical than tropical. But it depends on the situation; in the past there have been plenty of shallow-to-moderate warm-core systems as analyzed by this method which were officially classified as tropical cyclones, even hurricanes, and the nature of the winds in this case were more characteristic of a tropical cyclone. In any event, while there is a subtropical-vs.-tropical aspect given the subjectivity and limitations and gray areas involved, this duck was not walking, swimming, or quacking like a non-tropical one!]
By Dave Martin, AP