Actually yes ED, there is detailed classification for sub-tropical storms. Go to http://www.typhoon2000.ph/archives.htm#gp
Gary does very detailed study on the subtropical storm in May, he asked the best tropical meteorologists what they would do with a sub-tropical storm, it's pretty interesting.
" A quiet month of May followed the first April Atlantic tropical
cyclone on record. Since 1886 twelve tropical storms have formed
during May, with additional tropical depressions and subtropical storms
tracked. The last tropical storm to form in May was Tropical Storm
Arlene in 1981, which formed in the western Caribbean during the first
week of May. Following a May tropical storm in 1887 and a hurricane in
1889, no more May storms were detected until 1932. However, since 1932
the longest gap between May tropical storms has been eleven years (1959
to 1970 and 1970 to 1981). So the Atlantic basin is overdue for a May
tropical storm.

There was an interesting system off the southeast U. S. coast during
the first week of the month which initially seemed to have delusions of
developing into a subtropical storm. A meso-scale convective system
from the Gulf of Mexico had moved to a position off the North Carolina
coast by 2 May where it exhibited some rotation and had generated some
convection near the center. (This information from David Roth.)
According to Bob Hart, the Cyclone Phase Space had initially indicated
possible hybrid or even weak warm-core development, but later runs of
the program had backed off a bit and trended toward neutral or cold-
core evolution. And Chris Fogarty pointed out that with the upper-level
trough open to the northwest of the LOW, it would have been very
difficult for a warm-core cyclone to form."

Also I dug this classification out:
"Subject: A6) What is a sub-tropical cyclone?
A sub-tropical cyclone is a low-pressure system existing in the tropical or subtropical latitudes (anywhere from the equator to about 50°N) that has characteristics of both tropical cyclones and mid-latitude (or extratropical) cyclones. Therefore, many of these cyclones exist in a weak to moderate horizontal temperature gradient region (like mid-latitude cyclones), but also receive much of their energy from convective clouds (like tropical cyclones). Often, these storms have a radius of maximum winds which is farther out (on the order of 100-200 km [60-125 miles] from the center) than what is observed for purely "tropical" systems. Additionally, the maximum sustained winds for sub-tropical cyclones have not been observed to be stronger than about 33 m/s (64 kts, 74 mph)).

Many times these subtropical storms transform into true tropical cyclones. A recent example is the Atlantic basin's Hurricane Florence in November 1994 which began as a subtropical cyclone before becoming fully tropical. Note there has been at least one occurrence of tropical cyclones transforming into a subtropical storm (e.g. Atlantic basin storm 8 in 1973).

Subtropical cyclones in the Atlantic basin are classified by the maximum sustained surface winds:

less than 18 m/s (34 kts, 39 mph) - "subtropical depression",
greater than or equal to 18 m/s (34 kts, 39 mph) - "subtropical storm"
Prior to 2002 subtropical storms were not given names, but the National Hurricane Center issued forecasts and warnings similar to those for tropical cyclones. Now they are given names from the tropical cyclone list."
It's from the Hurricane research division page FAQ.
Hope that helps