ATL: INVEST 90L - Discussion

[Aric Dunn]

Don't look for recon to provide much more information than we're already receiving from the numerous surface obs in the northern Gulf. Here's a GARP plot of surface obs/satellite. I identified the LLC with the red crosshairs (28.2N/88.5W). The nearest significant convection is about 100 miles to the SW. Surface winds are peaking out at 25 kts. Lacking any persistent (or any at all) convection near the center, it would not qualify for upgrade to a TD by the NHC's own standards.

Shear may drop off briefly on Saturday morning just before the increasing westerly winds aloft ahead of the cold front reach the disturbance. That would be its best window of opportunity to get convection over the center and perhaps become "Nadine" before it's taken apart by increasing shear.

[img]http://home.comcast.net/~cgh57/90La.gif[/ig]

This buoy recently just reported winds of 42kts. appears to be stronger than it looks. fairly high background pressures could be the reason for it.


http://www.ndbc.noaa.gov/station_page.php?station=42360

That's about 135nm SW of the LLC in that heavier convection. Still wouldn't qualify for upgrade based on the exposed center.

you as well as many have seen TD come from exposed centers ... its happened a couple times this year already. by definition it has closed circ and persistent convection no matter how from the center the convection is.

[wxman57]

Convection has to persist over the center, not 130 miles away for qualification.

[Aric Dunn]

Convection has to persist over the center, not 130 miles away for qualification.

well the tell the NHC that. its happened many times with exposed centers.

in general I agree.

[SouthDadeFish]

A Windsat pass at 12Z today shows a rather surprisingly somewhat organized structure. In this 37 GHz pass, the pinks are ice scattering, representing deep convection, while the cyan colors are warm rain. You can see spiral banding attempting to form, but the circulation is pretty elongated from SSW-NNE.

[WeatherGuesser]

Good timing for the first big front! Here in Denver the high today will be 90 then the front comes through this evening, low tonight 49, and high tomorrow maybe only 70! This should definitely push anything that might develop out of the Gulf.

And that's supposed to cross the Mississippi sometime late Friday, so I'm not sure when that'll put it in play for the Gulf.

[wxman57]

Convection has to persist over the center, not 130 miles away for qualification.

well the tell the NHC that. its happened many times with exposed centers.

in general I agree.

I listened to Jack Beven explain that at the AMS conference this past spring with respect to the unnamed system that hit Florida from the east last year. The low lacked persistent convection over the center - persistent as being defined by lasting at least 6-12 hours. That disturbance only had convection over the center for a few hours near landfall. That's why they never named it.

P.S. That was Invest 93L of Oct 6-13, 2011.

[wxman57]

Good timing for the first big front! Here in Denver the high today will be 90 then the front comes through this evening, low tonight 49, and high tomorrow maybe only 70! This should definitely push anything that might develop out of the Gulf.

And that's supposed to cross the Mississippi sometime late Friday, so I'm not sure when that'll put it in play for the Gulf.

GFS has the leading edge of the front in the NE Gulf Saturday evening. Wind shear will be increasing ahead of the front, though.

[DukeDevil91]

Visible showing a pretty well defined LLC at 28.2N 88.5W. Give it some convection and this a depression. Looks to be moving SW at this point. Anyone know what the northerly shear is supposed to do within the next 24 - 48 hours?

[Aric Dunn]

Good timing for the first big front! Here in Denver the high today will be 90 then the front comes through this evening, low tonight 49, and high tomorrow maybe only 70! This should definitely push anything that might develop out of the Gulf.

And that's supposed to cross the Mississippi sometime late Friday, so I'm not sure when that'll put it in play for the Gulf.

GFS has the leading edge of the front in the NE Gulf Saturday evening. Wind shear will be increasing ahead of the front, though.

I agree that persistence is key, what is not always so cut a dry is when a system is producing persistent convection just not over the center. its a pretty fuzzy line some times and they have upgraded many times... as of right now I would not upgrade until the circ becomes more defined. The convective pattern is of a sheared system.

[cycloneye]

2 PM TWO stays at 40%,Recon Postponed

AN ELONGATED AREA OF LOW PRESSURE CENTERED ABOUT 75 MILES SOUTHEAST
OF THE MOUTH OF THE MISSISSIPPI RIVER HAS BEEN DRIFTING SOUTHWARD
DURING THE PAST FEW HOURS. SINCE THE SHOWER ACTIVITY ASSOCIATED
WITH THE LOW REMAINS POORLY ORGANIZED...THE AIR FORCE
RECONNAISSANCE MISSION SCHEDULED FOR TODAY HAS BEEN POSTPONED TO
TOMORROW. THERE IS STILL POTENTIAL FOR SOME DEVELOPMENT DURING THE
NEXT DAY OR SO BEFORE ENVIRONMENTAL CONDITIONS BECOME UNFAVORABLE.
THIS WEATHER SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF BECOMING
A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

[Aric Dunn]

interesting... I guess we wait.

[GCANE]

Looks like an anti-cyclone is beginning to form over this.

http://tropic.ssec.wisc.edu/real-time/s ... 000&loop=0

http://www.spc.noaa.gov/exper/mesoanaly ... sector=18#

[wxman57]

Buoy back to 15 kts.
http://www.ndbc.noaa.gov/station_page.php?station=42360

[otowntiger]

It doesn't appear to qualify for TD status now. I didn't see the center tucking under the convection in that satellite loop, by the way. It did look like the LLC may have weakened/opened up a bit on that loop, though. Pressures are actually 2mb higher in the area since yesterday. I think we have a high probability of a weak/sheared TD/TS in the NE Gulf tomorrow/Saturday tracking across the FL Peninsula on Sunday as it merges with the front. Should be relatively fast-moving across Florida, meaning less of a rain threat and no wind threat.

Thanks. So my fancy Davis weather station anemometer still won't be getting a work out. I've had the thing for 3 years and the strongest wind recorded so far (not applied by a a leaf blower ) was in a fast moving squall from Isaac last Monday: a whopping 38 mph! So I'm guessing this system will be even more tame for us here.

[Aric Dunn]

Buoy back to 15 kts.
http://www.ndbc.noaa.gov/station_page.php?station=42360

yep the convection has passed to its south.

[CalmBeforeStorm]

This is a sheared, naked swirl that has at most two days to organize before it is sheared apart and swept away by the approaching cold front. Not of much interest.

[otowntiger]

This is a sheared, naked swirl that has at most two days to organize before it is sheared apart and swept away by the approaching cold front. Not of much interest.

So far I agree. Of course every system has to come from somewhere so you never know. 2 days could be plenty of time if the conditions are right. Although I don't think they will be conducive enough and/or long enough for there to be much worry.

[tolakram]

Latest:

[ROCK]

exposed....decapitated..naked... wont be much left if it doesnt fire off some more convection soon.....

[wxman57]

exposed....decapitated..naked... wont be much left if it doesnt fire off some more convection soon.....

Yes, convection is further separating from the LLC. No upgrade today. Shear just too strong. That's good. Don't need any more Gulf action this year.