Looking at the latest imagry on delta, what is catching my attention the most is how the storm is now operating in isolation, there doesn't seem to be any attached fronts. I would argue the storm is more tropical in nature than sub tropical at this point, but it's still got a big windfield, Seeing some rain flagged 50Kt winds near the center. hmmmm, Personally I'd have classified, it, but they'll probably wait until an eyelike feature develops (which seems to be happening).

for an example of a similar storm. Olga in 2001 comes to mind. the cloud tempratures never got really cold, in fact I think the current invest has tempratures as cold as olga ever had, even when it had a well defined eye.

http://www.nhc.noaa.gov/2001olga.html

-Mark