Re: so what does it mean to be a 35 knot low again?
Posted by Chris in Tampa on 8/5/2010, 4:15 pm
I'm not sure exactly. I think they say it is a low perhaps when the circulation may not have a closed surface wind field, but there is a low enough pressure area associated with it that might be defined well enough that it is not a low pressure trough (a wave). A wave would not have a closed circulation of course and the pressure would be low along the trough.

That is what I think. I would think at this point it meets the criteria for becoming a tropical storm again, but we'll see.

On August 3rd the NHC discussion started with this when the last advisory was issued for Colin:

"THE CENTER OF COLIN PASSED NEAR OR OVER THE WOODS HOLE NTAS BUOY
ABOUT 15Z...WHICH REPORTED A MINIMUM PRESSURE OF 1007 MB AND A
SMALL LOW PRESSURE CENTER.  HOWEVER...NEITHER THAT BUOY NOR THE
NEARBY NOAA BUOY 41040 REPORTED WINDS SUPPORTING A CLOSED
CIRCULATION...AND WESTERLY WINDS ARE NOT CURRENTLY APPARENT IN LOW
CLOUD MOTIONS SOUTH OF THE CENTER.  ADDITIONALLY...THE ASSOCIATED
CONVECTION HAS BECOME VERY DISORGANIZED.  BASED ON THIS...COLIN HAS
DEGENERATED INTO A REMNANT LOW WITH GALE-FORCE WINDS OVER A SMALL
AREA NORTH OF THE CENTER.  "

From the Glossary of NHC Terms:

"Remnant Low:
A post-tropical cyclone that no longer possesses the convective organization required of a tropical cyclone...and has maximum sustained winds of less than 34 knots. The term is most commonly applied to the nearly deep-convection-free swirls of stratocumulus in the eastern North Pacific."

So Colin no longer had a closed circulation and could not be a tropical storm or depression. But, it did have a small enough low pressure area that I guess was defined well enough that it was not considered a wave. Then when recon investigated yesterday they went down another notch, to wave. The 2PM EDT info today might have been based on early recon before they had a chance to review a westward wind shift, but decided it was well defined enough to be considered a low, but until more recon at the center was available, they were not willing to jump to it has west winds and a well defined enough wind field to say it is a closed LLC and make the jump back to tropical cyclone. (in this case, tropical storm given its winds)

That's my thoughts on it, but I'm not 100% sure.
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Recon in the Air - JAC, 8/5/2010, 12:48 pm
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