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Tropical vs. Subtropical Storm: What's The Difference
May 23, 2023 at 07:57 PM EDT
By Weatherbug Meteorologist John Benedict
With the start of hurricane season approaching, it’s not uncommon to hear about subtropical cyclones. Let’s look at what defines a subtropical cyclone and how they form, and how they differ from tropical cyclones.
Most subtropical cyclones start out as typical extratropical cyclones with a cold core. Cold core systems derive their energy based on interactions between cold and warm air masses and the progression of fronts. Conversely, tropical cyclones are warm core systems that derive their energy from the warm waters (greater than 80 degrees) of the tropical oceans.
Subtropical cyclones generally form beneath upper-level lows or troughs of low pressure with a circulation extending down to the surface. Some subtropical systems can also originate from a mesoscale low which are typically embedded within frontal zones.
If an extratropical cyclone moves over waters of at least 70 degrees Fahrenheit, the cyclone will begin to have thunderstorm development, generally in a band to the east of the center. Over time, the cyclone condenses evaporated water vapor from the warm ocean waters below, releasing latent heat. Latent heat will help warm the core of the cyclone, making it subtropical. Subtropical cyclones are a hybrid type of storm that can gain their energy from both interactions between differing airmasses and latent heat release.
Subtropical cyclones are typically cloud-free surrounding the center of circulation. The thunderstorms associated with the cyclone are usually over 100 miles away from the center, typically north or east of the center. Unlike tropical cyclones, not as much precipitation is associated with subtropical ones due to the large area of dry air in the center that limits thunderstorm activity.
Subtropical cyclones can become tropical cyclones if it moves over warmer water, usually at least 80 degrees Fahrenheit, leading to the development of a warm core with thunderstorms activity filling in around the center. Subtropical storms that become tropical mainly remain at tropical storm strength, but there are a few cases when subtropical systems strengthened into hurricanes which happened back in 2016 with Hurricane Alex which occurred in January!
Subtropical cyclones with winds below 39 mph, are classified as subtropical depressions, while systems with winds exceeding 39 mph are called subtropical storms. Once a subtropical storm strengthens enough to have hurricane force winds, it is automatically assumed to have transitioned to a tropical cyclone. While subtropical cyclones can form during the traditional hurricane season, they often occur before or after the official hurricane season.
Look out for the term subtropical in the coming weeks as the tropics begin to heat up.
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Image: Subtropical Storm Beryl spins off the coast of the Southeastern United States on May 26, 2012. (NASA Terra/MODIS True Color)
Most subtropical cyclones start out as typical extratropical cyclones with a cold core. Cold core systems derive their energy based on interactions between cold and warm air masses and the progression of fronts. Conversely, tropical cyclones are warm core systems that derive their energy from the warm waters (greater than 80 degrees) of the tropical oceans.
Subtropical cyclones generally form beneath upper-level lows or troughs of low pressure with a circulation extending down to the surface. Some subtropical systems can also originate from a mesoscale low which are typically embedded within frontal zones.
If an extratropical cyclone moves over waters of at least 70 degrees Fahrenheit, the cyclone will begin to have thunderstorm development, generally in a band to the east of the center. Over time, the cyclone condenses evaporated water vapor from the warm ocean waters below, releasing latent heat. Latent heat will help warm the core of the cyclone, making it subtropical. Subtropical cyclones are a hybrid type of storm that can gain their energy from both interactions between differing airmasses and latent heat release.
Subtropical cyclones are typically cloud-free surrounding the center of circulation. The thunderstorms associated with the cyclone are usually over 100 miles away from the center, typically north or east of the center. Unlike tropical cyclones, not as much precipitation is associated with subtropical ones due to the large area of dry air in the center that limits thunderstorm activity.
Subtropical cyclones can become tropical cyclones if it moves over warmer water, usually at least 80 degrees Fahrenheit, leading to the development of a warm core with thunderstorms activity filling in around the center. Subtropical storms that become tropical mainly remain at tropical storm strength, but there are a few cases when subtropical systems strengthened into hurricanes which happened back in 2016 with Hurricane Alex which occurred in January!
Subtropical cyclones with winds below 39 mph, are classified as subtropical depressions, while systems with winds exceeding 39 mph are called subtropical storms. Once a subtropical storm strengthens enough to have hurricane force winds, it is automatically assumed to have transitioned to a tropical cyclone. While subtropical cyclones can form during the traditional hurricane season, they often occur before or after the official hurricane season.
Look out for the term subtropical in the coming weeks as the tropics begin to heat up.
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Image: Subtropical Storm Beryl spins off the coast of the Southeastern United States on May 26, 2012. (NASA Terra/MODIS True Color)