SOUTH MISSISSIPPI (WLOX/AP) - Alberto became a subtropical storm on Friday morning
But, what exactly is a subtropical storm and how is it different from a tropical storm?
As far as overall impacts, there is little difference between a tropical storm and a subtropical storm: they both produce strong winds and heavy rain. It's mainly a technical change in the structure of the storm.
There are three different types of systems: tropical, subtropical, and extratropical.
Extratropical systems are the big red 'L's that we are used to seeing on the weather map across the US every day. They are cold-core weather systems that can form over land or water. They typically have a cold front or warm front associated with them. Winds in an extratropical system can be less than 35 mph and can exceed 74 mph; their maximum winds can be located throughout a broad area away from their centers.
Tropical systems are warm-core weather systems that only form over water. They have no fronts associated with them but typically generate more rain than extratropical systems. Their strongest winds are located near their center, or sometimes, eye. Tropical systems have more enhanced thunderstorm activity concentrated immediately surrounding their center. And, given the right conditions, these tropical systems can quickly become strong hurricanes.
Subtropical systems are a cross between an extratropical and a tropical system, having characteristics of both. They can be warm- or cold- core. As long as a subtropical systems remains subtropical, it cannot become a hurricane. A few tropical facts: Subtropical Storm Ana is one of the earliest forming tropical or subtropical system in the Atlantic since a storm of the same name in April 2003. However, since 2000... Tropical Storms Alberto (5/18/12), Beryl (5/25/12), Arthur (5/30/08), Barry (5/30/07) and Subtropical Storm Andrea (5/6/07) also formed during the month of May.
So, seeing named storms before the official start to the Atlantic hurricane season (June 1) is not typical, but not unheard of. And keep in mind that just because a named storm forms before hurricane season officially begins, it doesn't necessarily mean that the season will be more or less active.