Subtropical cyclone

Subtropical cyclones are a type of hybrid storm, somewhere between extratropical cyclones (which are a paired warm front and cold front rotating around a strong low pressure system made even stronger by contact with the jet stream) and tropical cyclones (non-frontal storms created by warm ocean waters and tropical convection, and also called 'hurricanes'). They are created when an extratropical cyclone moves out over warm subtropical waters and begins to pick up moisture and heat in the manner of a hurricane, even though its origin is completely different from a hurricane.

Since the cyclonic effect already exists, the sea surface doesn't need to be as warm for a subtropical cyclone to be created as it does for a tropical cyclone. 68 Fahrenheit, as opposed to 80 Fahrenheit, is enough for subtropical cyclogenesis. Like a tropical cyclone, the subtropical cyclone lacks distinct weather fronts within its structure -- it becomes one uniform temperature and exists separate from frontal systems. Unlike a hurricane, however, its winds remain quite weak, seldom rising above 70 miles per hour.

If a subtropical cyclone remains in subtropical latitudes or moves back north, it will resemble a weaker version of a hurricane in its behavior and effects, and will eventually dissipate. If it moves south over the warm equatorial waters, however, it may well strengthen and change character, becoming a full-fledged hurricane. It may then return north as a hurricane or typhoon, having changed completely from its original extratropical nature, to batter coastlines with storm surges and massive winds before collapsing and melting away over land.

Subtropical cyclones are a rather broad and vague family of storms, and there is still some doubt about how to classify them among meteorologists. They are an interesting study, however, in how a storm moving from one area to another on the Earth's surface can transform into a completely new form as the temperature, moisture, and pressure conditions of different areas of the globe work upon its structure.