Subtropical cyclone

[irvingr5]

One TV weatherman said this morning on a Charleston, SC, station that Andrea is called "subtropical" (not "tropical") because it began as a cold core system. However, a different TV weatherman said it was subtropical because the core was warming up, but not a hot core yet. I understand that it was upgraded to subtropical because it now has a tight, closed circulation at the center. Does that automatically mean it has a hot core?

Actually, I have several questions. The temps are not quite 80 degs F, which I learned was the minimal temperature to provide the latent heat for a tropical cyclone. So, if the core is hot, or warming, where is the energy coming from, as the SSTs are not warm enough? As a corollary question, in a barometric (?) (not sure if that's the right word) low pressure, what is the source of the energy? (Possibly the clash of different temperature air masses providing convection?)

[Christina514]

I found some information on this for you, I hope it helps.


A sub-tropical cyclone is a low-pressure system existing in the tropical or subtropical latitudes (anywhere from the equator to about 50°N) that has characteristics of both tropical cyclones and mid-latitude (or extratropical) cyclones. Therefore, many of these cyclones exist in a weak to moderate horizontal temperature gradient region (like mid-latitude cyclones), but also receive much of their energy from convective clouds (like tropical cyclones). Often, these storms have a radius of maximum winds which is farther out (on the order of 100-200 km [60-125 miles] from the center) than what is observed for purely "tropical" systems. Additionally, the maximum sustained winds for sub-tropical cyclones have not been observed to be stronger than about 33 m/s (64 kts, 74 mph)).

http://www.aoml.noaa.gov/hrd/tcfaq/A6.html

[irvingr5]

Thanks, Christina514. A link in your cite (https://courseware.e-education.psu.edu/public/meteo/subtropical_cyclones.html) also gave me the source of baroclinic low pressure areas: temperature gradients.

[Christina514]

Great !!! Glad I could help! I am no expert but I like to do searches so anytime, just ask.

[ROLLTIDE]

Tropical:
Relatively small (~ 100 mile) wind fields, with highest winds very near the center
Unattached to fronts
Convection concentrated near the center
Deep convection (i.e., thunderstorms)

Nontropical:
Generally very large, upwards of 300-400 mile windfields.
Often attached to fronts or the remnants of them.
Convection generally in a large band far from the center
Shallow convection outside of said band <!--IBF.ATTACHMENT_468242-->