Thu Nov 11 2004 11:59 PM
Re: 91L & 92L

I agree -- neither has a really good shot at developing.

While we may see trough fracture occur over the far eastern Atlantic, with a large ridge in place over the east Atlantic and west Europe, the "hybrid" low is gradually feeling the influence over the broad trough and is starting to become sheared. I think it's window has pretty much closed.

It is on the tail end of this same trough where the other invest has been, but the convection is very much cyclical and is in a region of decent shear. There may be some weak baroclinic development along the trough with a weak low moving north & east with time, but tropical - or even hybrid - development is pretty unlikely. Last QuikSCAT pass showed a weak circulation in the eastern Caribbean and there is some convection, but it's sheared and isn't organized. There's some pretty cold (relatively speaking, of course) air behind the trough as well, as evidenced by the alto- and stratocumulus over the western Atlantic; the temperature gradient along the trough is likely enhancing convection, but isn't conducive to any development.

But, all of these interesting "hybrid" storms raises an interesting point -- what is, or should be, the operational definition of a subtropical cyclone? To me, it seems like it has been somewhat ambiguous this year, particularly since we cannot fly recon out to these storms to accurately gauge their structure and the funding isn't there (yet) to use the remotely-sensed data, such as microwave data, to determine the structure of the storm on a real-time basis. We had Nicole, a subtropical storm, while we also had Matthew, a storm that likely was only classified as a tropical cyclone (as opposed to an extratropical storm) because of recon. Further, there have been about 5 other storms you could theoretically classify as subtropical cyclones, some more impressive than others (and some more impressive and longer-lasting than some of our existing storms), that were not.

The recent decision to include subtropical cyclones in the storm record -- and the subsequent increased analysis for these storms, in terms of operational attention focused to what is out there -- and the rather, well, discontinuous system of classifying them is skewing the climatological record for the Atlantic basin. Furthermore, I don't feel that there is an accurate or concrete enough definition of what one of these storms is to justify including them with the tropical season climatology. It seems that the definition of what a subtropical cyclone is has been "not extratropical but not tropical." That implies a warm-core system with a large radius of maximum winds, or a cold-core system with a small radius of maximum winds, or an occluded-looking low with some convection near the center, but what is the *actual* definition of these storms?

I'd like to get everyone's thoughts on the issue, since it seems to be somewhat the hot topic in the Atlantic over the past couple of months. Obviously, the field deserves much more research and analysis. But, given that there is little such work currently ongoing, should we classify these storms within the Atlantic season climatology, or should we classify them separately (i.e. "Subtropical Storm 1") as before? Further, what about systems in the Pacific & other basins -- the WPac sees a couple of similar systems each year, while the Indian Ocean has numerous "monsoon depressions" each year that affect the coastline during the season but are not true tropical cyclones. Where do you draw the line? To me, it should be consistant throughout the world, but that's just my opinion.

With the loss of life these systems can bring -- see the May Haiti storm -- it is obvious that some attention should be paid to these systems. But do they deserve to become a part of the tropical cyclone climatology as named storms? My personal belief is no, at least not until we can better quantify what these storms truly are -- are they closer to extratropical than tropical, etc. -- but that there should be some classification scheme nonetheless, one that is applied consistantly with at least a rough operational definition. But, I'd like to get everyone's thoughts, as I mentioned before, on the topic...

Here's hoping the season is over...

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