I live in the freakin’ hurricane capitol of the known universe. Its important that I keep up with storms.
Last night the Weather Channel made a big deal about Gustav, the latest storm off the coast, by saying that it was the very first NAMED SUBTROPICAL STORM in history. With that , they proceeded to do an unbelievably bad job of telling us what that all meant, complete with text graphics actualy on top of text graphcs, making them impossible to read.( believe me, my wife and I were paying attention and we both looked at each other and haid “huh?”)
Could someone please tell me what distinguishes a tropical storm from a subtropical one?
Thanks
hrm…first named subtropical storm, huh? The Weather Channel sure has a short memory - see this link..
I think what they meant to get across was that this was the first year that National Hurricane Center is authorized to name subtropical/extratropical storms from the same list as hurricanes (before, they had just been using numbers), to give more weight to the seriousness of these storms - while not tropical, they can still pack a punch and be extremely dangerous (The Perfect Storm gives you an idea how powerful these “non-hurricane” storms can get).
Anyway, IANAM, but http://www.usatoday.com/weather/wstypes.htm has a good description of the differences between extratropical and tropical systems.
critter42
Weeks, I’ve been wondering the same thing; is it raining in your part of Costal NC yet? I think we’re supposed to get it tonight.
Anyway, according to http://www.nhc.noaa.gov/aboutgloss.shtml a subtropical storm is:
A subtropical cyclone (from the same link) is described as:
Or, somewhere between a tropical and extratropical system in the link critter42 provided (which didn’t work for me: try this.)
I think that it’s also noteworthy that–despite the more innocent sounding “sub-” name–the wind speeds in a subtropical storm are similar to those in tropical storms:
Sorry for my multi-post; for some reason, I keep feeling compeled to click “Submit Reply” this morning instead of the down-scroll arrow and I don’t know why.
Nah, 5:30 am here, and nothing! :o
In a nutshell, a tropical system (depression, storm, or hurricane) gets its energy from the latent heat of the water (condensation). The low pressure area at the surface causes this moisture-ladened air to rise and condense, something we see as convection because of the counter-clockwise rotation of a cyclonic system in the northern hemisphere. In the higher altitudes, there is high pressure, which causes the air to sink. Thus, at the center of a tropical system, the air is sinking (thus, the calm in the center), but convectional activity surrounds this sinking air. If the pressure at the higher altitudes is not high, the system cannot get very strong (not over 60 mph, usually) and the system is not completely tropical. Impeding the progress of tropical systems is another factor: shear, which is caused by strong winds aloft blowing the convection away from the center. This is what happens also if there is a low pressure aloft, rather than a high pressure.
Gustav, until recentl, had low pressure aloft and the convection shifted away from the center. I believe, but I haven’t checked, that this low pressure aloft has subsided and that the convection is now at the center. Presto: a tropical system.
Edouard was also hampered by very high shear winds and never developed very strongly, but it was still called a tropical system, which IMHO was a misnomer.
Tropical systems are given names once they reach “storm” status, which is 39mph or greater. 74mph or greater are called hurricanes. They are given numbers once they form a depression, less than 39 mph, but with a definite center. If no center can be found, they are called troughs or disturbances. This is the first year that NHC has allowed names for sub-tropical systems.
Once a tropical system is given a name, it retains that name even though it no longer earns it. If a hurricane weakens into a tropical depression, it retains its “storm” name. Many hurricanes become “extra-tropical” when they reach the colder waters of the Canada Maritimes. Sea surface temperatures must be at least 80 degrees F to provide the latent heat needed. When the system reaches colder water, the energy supply is gone and it is no longer tropical. There still may be low pressure and rains, but this is caused by non-tropical causes: the temperature changes of the air caused by a cold front. This is what happens in the continental USA. The extra-tropical hurricane is usually picked up by a cold front and moves along at the same pace as the front, which is usually 20-30mph.
Didn’t I post that exact definition and link yesterday? Thanks for the extra elaboration, though, barbitu8.
Weeks, we’ve been getting it today pretty good. Constant rain, but the wind hasn’t been too bad. The center’s right over–or damn near–Cape Hatteras right now.
I knew I saw it somewhere. 