What makes Alberto a Subtropical Storm?
The classification of a storm is determined by the formation of the storm. Alberto was classified as a Subtropical Storm because of how it interacted with the water and atmosphere.
Storms are either “Warm Core” or “Cold Core” depending on how they are formed. Tropical Storms and Hurricanes are Warm Core storms as they form over warm water surrounded by warm air. Cold Core storms are low-pressure storms that cause cooler air when they go by. Alberto is a combination of the two.
Alberto’s development over 80-degree water and warm, humid air usually would have caused a Tropical Storm classification, but because Alberto had high winds and colder temperatures from the atmosphere above the development was subtropical.
The National Hurricane Center defined a subtropical storm as:
“A subtropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 34 kt (39 mph or 63 km/hr) or more.”
A subtropical cyclone as defined by the National Hurricane Center is:
“A non-frontal low-pressure system that has characteristics of both tropical and extratropical cyclones. Like tropical cyclones, they are non-frontal, synoptic-scale cyclones that originate over tropical or subtropical waters, and have a closed surface wind circulation about a well-defined center. In addition, they have organized moderate to deep convection, but lack a central dense overcast. Unlike tropical cyclones, subtropical cyclones derive a significant proportion of their energy from baroclinic sources, and are generally cold-core in the upper troposphere, often being associated with an upper-level low or trough. In comparison to tropical cyclones, these systems generally have a radius of maximum winds occurring relatively far from the center (usually greater than 60 n mi), and generally have a less symmetric wind field and distribution of convection.”
Hurricane Season officially begins on June 1st so make sure you’re Prepared for whatever kind of storm comes your way!