The 5:30 TWO is crystal clear on this:

530 PM EDT THU SEP 20 2007
FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

AN AIR FORCE RECONNAISSANCE PLANE FOUND A WELL-DEFINED AREA OF LOW
PRESSURE IN THE GULF OF MEXICO ABOUT 115 MILES WEST-SOUTHWEST OF
TAMPA FLORIDA. THIS SYSTEM IS ACCOMPANIED BY STRONG GUSTY WINDS IN
A FEW SQUALLS BUT THE OVERALL THUNDERSTORM ACTIVITY REMAINS LIMITED
AND DISORGANIZED. ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR THIS
SYSTEM TO BECOME A SUBTROPICAL OR TROPICAL CYCLONE AT ANY TIME
DURING THE NEXT 24 HOURS.

Looks like a very reasonable statement. Really, they probably could have gone either way this afternoon - start tracking 93 as an STD, or not. While it already loosely fits the definition of a subtropical depression, it would be a generous upgrade, for now.

Very glad to see that they mentioned the low centered near 33N 47W, as well. Another one currently attempting to acquire subtropical and/or tropical characteristics.

Finally, as many of us have been mentioning, the southern and/or western Caribbean is firing back up a bit, and is starting to have some occasional model support for development.