SARASOTA, FL (WWSB) - Alberto is still a Subtropical Storm as of 8 AM but that could chance later today as it appears to be taking on a more tropical look. Aircraft observations indicate a pressure drop and the center has reformed closer to the center of strong thunderstorm activity.
So what is the difference between our three main classes of storms named Tropical, Subtropical and Extratropical. A good analogy can be had with the hot air balloon and fireplace examples.
In a tropical storm the system gets it's energy from the warm tropical water which feeds thunderstorms which release heat which supplies the energy to keep the feed back loop going. So long as nothing prevents the growing thunderstorms from releasing heat the system will grow. If the winds aloft don't rip the thunderstorms apart or prevent the thunderstorm's from venting at the top with the characteristic spiral bands we see on satellite, then the heat and moisture will rise, cool and condense then vent away and allow more storms to grow, rise, cool and condense moisture into rain. Think of it like a fireplace. you throw in logs at the hearth (think warm tropical water), the fire starts (think thunderstorms) and the smoke rises up the chimney (think outward moving spiral clouds seen from space by satellite). So long as there is wood and no one clogs the chimney then the fire will grow. That's your hurricane.
Now think of the hot air balloon. The balloon rises until it no longer does. The pilot turns on the burner and heats the air. The air becomes hotter than the surrounding air around the balloon. Hot air is lighter than cool air so the hot air is buoyant and starts to rise. How do you make it rain. Take hot moist air and make it rise, cool and condense. The hot air balloon example is your extratropical system such as we get in the winter.
Nor the Subtropical system is a storm that has attributes of both the tropical and subtropical thermo dynamical mechanisms but it not purely either one.