A great follow-up from CC above. A few of those observations probably can do with a little extra information, so as not to leave anyone with more confusion than such a thread is already bound to create

Contrary to what CC may have seemed to imply, temperatures of at least 27C (80F) are not always a necessary ingredient to cook up a warm core. Depending on the temperature of the atmosphere above, and other factors, tropical cyclogenesis can, and often does, occur, in regions where water temps are running considerably below the oft-cited 27C.

The most recent example of this was just last week, as TD-1 formed over water temps that were averaging about 25-26C.

To digress a moment while on the topic of 2009's TD-1, here's a little bit of tropical cyclone trivia that might be of interest: Last week's TD was actually the farthest north any official preseason tropical or subtropical cyclone has ever formed in the Atlantic basin!

Another point of clarification worth noting - While by very definition Tropical Cyclones are warm-cored systems, Subtropical Cyclones can be either neutral, or warm core. Given that 92L was generally neutral, with some hints of an incipient warm core trying to become established with the aid of some warm seclusion that had already taken place, it is probably not unreasonable to refer to it as a bona fide subtropical cyclone, despite not being named.

There has been some research that strongly suggests that there are actually far more subtropical cyclones than have been named. Generally speaking, those subtropical cyclones that actually do get a name, or that get added posthumously as a hurricane season "storm," either have a more 'classic' structure to them than usually the case.. as these are hybrids, it is not surprising then that some are only added after the fact, having been extensively reviewed in the post-season, and found to have been sufficiently developed for the post-season upgrade. A recent example of this is the '2005 Unnamed Subtropical Storm' (PDF), which was thought to be mostly extra-tropical, until more thorough examination of the system determined it to qualify for inclusion in the 2005 Atlantic hurricane season record books.

Finally, and as this can add extra 'fuel' to many another fire, we won't discuss the how and why of it, the trends of recent decades are for the tropics, and thus warmer SSTs, to be expanding ever poleward. In addition, air and SST temps are also already increasing fastest in the higher latitudes, as it is. Whatever the cause of this trend, an obvious consequence of these ever-expanding warmer waters, is a greater percentage of the earth being covered in SSTs that are more and more supportive of tropical and subtropical cyclogenesis... certainly an interesting development for those of us that track these storms.