Ex Invest 99L in Western Atlantic

[cycloneye]

Yes,I think that is the answer to the number change.

[curtadams]

Convectionless now, sure, but one burst of convection would make this a TD by any reasonable definition. We know it could pop out convection because it did so last naight. So given that this is a system that basically could become a TD at any time an invest seems obligatory.

Oh, and I *so* agree with Wxman57 on the consistency issue! Although I break to the side that if it's got a closed circ, convection, warm core indicators, and a 20 kt wind it's a TD, period. I don't think the NHC should refuse to label a TD because they *expect* it to die quickly - our predictive abilities just aren't that good.

[littlevince]

I think 97L was deactivated (on 24 or 25 July) and come back with the same number, but maybe I'm wrong.

[gatorcane]

I agree, it needs a nice burst of sustained convection around the LLC and it should immediately be a TD. Let's see when it happens....looks like convection is on the decrease currently so no upgrade in the near-term.

[Weatherfreak14]

Convection trying to get going again????? http://www.ssd.noaa.gov/goes/flt/t1/loop-vis.html

[gatorcane]

Yeah there is a small flare up on the west side of the Low's center. I think its consuming alot of dry air also so that is inhibiting development at least for now.

Movement has leveled off to 270 just above 18N and very fast also. It may not lose much more lattitude at this point and is about as far south as it will ever be.

[Derek Ortt]

http://manati.orbit.nesdis.noaa.gov/dat ... Bas112.png

above is a reason why this is not a TD... no closed circulation at the surface

[cycloneye]

393
ABNT20 KNHC 011757
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI AUG 1 2008

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

SHOWER ACTIVITY IS VERY LIMITED IN ASSOCIATION WITH AN AREA OF LOW
PRESSURE OVER THE EASTERN ATLANTIC ABOUT 750 MILES WEST OF THE CAPE
VERDE ISLANDS. ALTHOUGH ATMOSPHERIC CONDITIONS ARE CURRENTLY NOT
VERY CONDUCIVE...SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE AS IT
ENCOUNTERS SLIGHTLY WARMER WATERS DURING THE NEXT COUPLE OF DAYS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER KNABB

http://asp1.sbs.ohio-state.edu/tropical ... c/outlook/

[gatorcane]

was about to post the TWO but not fast enough to beat the "eye"

[wxman57]

http://manati.orbit.nesdis.noaa.gov/dataimages21/cur_hires/zooms/WMBas112.png

above is a reason why this is not a TD... no closed circulation at the surface

Derek,

That link above is to an image that misses the system completely. It certainly appears to have a well-defined LLC on visible satellite imagery. I realize that sometimes these circulations that we see on satellite are not quite down to the surface, but this one sure looks like a surface circulation.

Here's a McIDAS shot. Of course, it sort of lost its convection now.

[Derek Ortt]

the pass is from 0740 UTC, It could have been where the trough was depicted by QS

of course, QS may have depicted an obvious closed circulation as a wave like it did TS Bertha

[AJC3]

http://manati.orbit.nesdis.noaa.gov/dataimages21/cur_hires/zooms/WMBas112.png

above is a reason why this is not a TD... no closed circulation at the surface

Derek,

That link above is to an image that misses the system completely. It certainly appears to have a well-defined LLC on visible satellite imagery. I realize that sometimes these circulations that we see on satellite are not quite down to the surface, but this one sure looks like a surface circulation.

Here's a McIDAS shot. Of course, it sort of lost its convection now.

Chris, I don't think it missed it at all. At 0745UTC the system was up around 18.5 33W, and that's pretty much spot on (at the west edge of the swath) where QS depicts the vort center. Since it's moving at a pretty decent clip westward (close to 20kt), most if not all of the S/R westerly flow on the south side of the vort is getting counteracted at the surface by its' forward motion. If it has a closed sfc circ, and it may not, it's very, very tiny.

Given all the considerations...stable air, limited, intermittent convection, and some question about whether the system is closed at the surface, one can't be surpirsed about a lack of an upgrade since it left the coast, although I strongly suspect this was a bona-fide TD as it was moving NW just of the coast.

[littlevince]

RGB loop

[curtadams]

I wasn't arguing that it deserved to be upgraded to a TD now - or even last night, since a closed surface circulation wasn't demonstrated last night TTMOMK. I was just saying it deserved an invest without question because it's so close. That's a really sharp wave circulation on the quickscat! In terms of calling it one now, the requirement for a formally closed surface circulation will miss some functioning tropical systems which are weak enough and moving fast enough. But that's not a consistency issue, that's a definitional issue. I don't see any good alternative to the formal surface circulation requirement. If I had my druthers, it would have been TD 5 east of the Cape Verdes, and right now either Tropical Low 5 or Tropical Remnant 5 depending on the closed circ formality.

[wxman57]

I don't think it missed it at all. At 0745UTC the system was up around 18.5 33W, and that's pretty much spot on (at the west edge of the swath) where QS depicts the vort center. Since it's moving at a pretty decent clip westward (close to 20kt), most if not all of the S/R westerly flow on the south side of the vort is getting counteracted at the surface by its' forward motion. If it has a closed sfc circ, and it may not, it's very, very tiny.

Given all the considerations...stable air, limited, intermittent convection, and some question about whether the system is closed at the surface, one can't be surpirsed about a lack of an upgrade since it left the coast, although I strongly suspect this was a bona-fide TD as it was moving NW just of the coast.

I went back and checked the position for 0740z and it was around 33.5W, so QS was looking at least at the eastern half. There wasn't much in the southern part except for some very low clouds. I'm not sure if QS would be able to identify westerly winds from that. I would still argue for consistency. If this isn't a TD in the open Atlantic, then it isn't one if it was in the Gulf. I'll make a note to ask Bill Read about this kind of situation next time I run into him. I'm sure he'll say they don't upgrade these things out to sea because they're not affecting anyone, and likely won't affect anyone.

[gatorcane]

convection on the increase again right over the center:

[CrazyC83]

Could this have been affected by external forces, kinda like TD10's remnants into TD12/Katrina in 2005? Could that be the reason for the number change?

[AJC3]

I don't think it missed it at all. At 0745UTC the system was up around 18.5 33W, and that's pretty much spot on (at the west edge of the swath) where QS depicts the vort center. Since it's moving at a pretty decent clip westward (close to 20kt), most if not all of the S/R westerly flow on the south side of the vort is getting counteracted at the surface by its' forward motion. If it has a closed sfc circ, and it may not, it's very, very tiny.

Given all the considerations...stable air, limited, intermittent convection, and some question about whether the system is closed at the surface, one can't be surpirsed about a lack of an upgrade since it left the coast, although I strongly suspect this was a bona-fide TD as it was moving NW just of the coast.

I went back and checked the position for 0740z and it was around 33.5W, so QS was looking at least at the eastern half. There wasn't much in the southern part except for some very low clouds. I'm not sure if QS would be able to identify westerly winds from that. I would still argue for consistency. If this isn't a TD in the open Atlantic, then it isn't one if it was in the Gulf. I'll make a note to ask Bill Read about this kind of situation next time I run into him. I'm sure he'll say they don't upgrade these things out to sea because they're not affecting anyone, and likely won't affect anyone.

I think if you asked him, or any of the specialists to a person, they'd give you that same answer. I won't go into the whole "course of least regret" (i.e the NHC/NWS mission) versus the need for "scientific consistency" since I'm sure you've heard it before. I think you and I might agree that things are done differently in the current operational setting than they would be if NHC was just a strict scientific entity - i.e. only concerned with the scientific aspect of TC analysis and forecasting (getting it right whilst being consistent being their top priorities), as opposed to their (our) mission of protection of life an property.

Then again, there probably wouldn't be nearly as much debate/dialogue...which I would find kind of boring.

[AJC3]

Could this have been affected by external forces, kinda like TD10's remnants into TD12/Katrina in 2005? Could that be the reason for the number change?

Two different animals. There was no other force at work here. Apparently, it seems the criteria for changing an 'invest' number is different than it is for changing or keeping the number on a TC.

[Blown Away]

Slight WSW movement, we will see if this trend continues. Maybe the GFS & GFDL have a handle on 99L.

http://www.ssd.noaa.gov/goes/flt/t1/loop-vis.html