No. A sub-tropical storm is a hybrid tropical storm. It has the wind speeds of a tropical storm but not all of the tropical characteristics, meaning it is completely warm-core. It is a hybrid between a topical and extra-tropical system.
Their convection and strongest winds are usually on the north and northeast sides and the center of lowest pressure is usually sheered. They will usually transition to a warm-core system given enough time.
There are also sub-tropical depressions. They name them because they can be just as dangerous, mostly due to fresh-water flooding (heavy rain) as a regular tropical storm.