In terms of tropic terminology, "subtropical storm" is one you may not be as familiar with.
A subtropical storm features many characteristics of a typical tropical disturbance — most of its energy comes from a clash of warm and cold air. It may have a well-defined center and closed circulation.
But, the area of maximum winds is farther away from the center by more than 60 nautical miles, and the system can be more widespread, disorganized, and less symmetrical than your standard tropical storm and/or hurricane.
There are no 'fronts' associated with subtropical systems. As the system moves into cooler water, it becomes a "cold core" system. They generally produce less rain than what would be expected in a typical system.
Subtropical storms can strengthen, but it must obtain more warm-core characteristics before it could transition to a tropical storm or hurricane.