ATL: EX-Tropical Depression FIVE - Discussion

[KWT]

Hmmm not so sure Aric, it was barely a TS last time they upgraded and this time it actually has stronger support now then it did last time round.

I think it all depends on what recon finds in terms of the LLC strength, probably will struggle to get winds much above 25kts though I agree Aric!

[ColinDelia]

It seems there is/has been a fair amount of Northeast shear - quite obvious in the satellite presentation -
that will start to decrease as the low moves closer to the upper level high around the LA/TX border.

Here is the New Orleans Forecast Discussion which details this.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NEW ORLEANS LA
808 AM CDT MON AUG 16 2010

.UPDATE...
.SOUNDING DISCUSSION...
THE ATMOSPHERE REMAINS SATURATED AND UNSTABLE WITH A PRECIPITABLE
WATER VALUE OF 2.47 INCHES AND A LIFTED INDEX OF -5.6. THE PRIMARY
THREAT FOR STRONG SHOWERS AND THUNDERSTORMS WILL BE HEAVY
RAINFALL. A SURFACE INVERSION IS PRESENT ALONG WITH WINDS OUT OF
THE NORTH NEAR THE SURFACE AND OUT OF THE NORTHEAST ALOFT.

&&

.PREV DISCUSSION... /ISSUED 527 AM CDT MON AUG 16 2010/

SYNOPSIS...
SURFACE ANALYSIS SHOWS A BROAD AREA OF 1010 MB LOW PRESSURE OVER
THE EXTREME NORTHERN GULF OF MEXICO SOUTH OF THE WESTERN FLORIDA
PANHANDLE. SUSTAINED WINDS APPEARED TO BE AVERAGING AROUND 15
KNOTS WITH SOME HIGHER GUSTS OBSERVED IN AND NEAR CONVECTION ON
THE SOUTHWEST SIDE OF THE LOW. SHOWER AND THUNDERSTORM ACTIVITY
HAS BEEN VERY DISORGANIZED NEAR THE CENTER OF THE LOW...BUT
APPEARED TO BE SLOWLY INCREASING THE LAST HOUR OR TWO.

A BROAD CYCLONE EXTENDS FROM THE SURFACE UP TO AROUND 500
MB...THEN THERE IS ABOUT 20 TO 30 KNOTS OF NORTHEAST SHEAR IN THE
UPPER LEVELS AROUND 300-200 MB. LOOKING AT SATELLITE...ESPECIALLY
WATER VAPOR LOOPS...ALL THE UPPER LEVEL FEATURES FROM THE BAJA
MEXICO AREA TO THE NORTHERN GULF COAST ARE MOVING WEST IN THE WEAK
TROPICAL EASTERLIES.

SHORT TERM...
THE EAST TO WEST STEERING CURRENTS DESCRIBED IN THE SYNOPSIS
SECTION ARE LIKELY TO NUDGE THE SURFACE LOW WEST FROM SOUTH OF THE
FLORIDA PANHANDLE TOWARDS THE SOUTHEAST LOUISIANA COAST LATE
TONIGHT AND EARLY TUESDAY MORNING. THE LARGER SCALE...CONVENTIONAL
MODELS ALONG WITH AND TROPICAL CYCLONE MODEL TRACK GUIDANCE ARE IN
PRETTY GOOD AGREEMENT AND FIT THE OVERALL PATTERN VERY WELL. OF
COURSE...THE BIGGER PROBLEM AS ALWAYS IS INTENSITY...AND THIS HAS
BEEN A PROBLEM ALL YEAR WITH WEAKER TROPICAL LOWS AND DEPRESSIONS.
THE RUC MODEL APPEARS TO HANDLE THE 250 MB WIND FIELD BETTER
ACROSS THE LOW PRESSURE AREA AROUND 12Z THIS MORNING...SHOWING
VALUES CLOSER TO REALITY AT 15 TO 20 KNOTS VERSUS THE NAM AND GFS
WHICH ONLY SHOW 5 TO 10 KNOTS. EVENTUALLY...THE LOW PRESSURE AREA
WILL COME UNDER LESS NORTHEASTERLY SHEAR IN THE UPPER LEVELS AS IT
MOVES CLOSER TO THE UPPER HIGH TO THE NORTHWEST.

GIVEN THE CURRENT OBSERVATIONS AND RADAR PRESENTATION...I AM NOT
EXPECTING RAPID DEVELOPMENT OF THE LOW INTO A TROPICAL
CYCLONE...BUT THAT COULD HAPPEN LATER TODAY OR TONIGHT IF
DEEPER...MORE SUSTAINED AND CONCENTRATED CONVECTION DEVELOPS NEAR
THE LOW CENTER.

[wxman57]

Recon won't be able to provide much additional info for a system that's embedded in a region with more surface obs than any other part of the entire Atlantic Basin. Obs confirm a weak surface low near 28.9N/86.2W. Winds around the low average around 15 kts, though there could be a few 20-25 kt winds in the heavier squalls that are being sheared to the southwest of the low center. Central pressure is about 1011.5mb, give or take a few tenths depending on how well the barometer of the nearby buoy has been calibrated.

What more do you expect to learn from recon today?

[Steve]

JB's take. Haven't watched it yet though.

http://www.accuweather.com/video/586320 ... e-gulf.asp

[vbhoutex]

The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or storm2k.org. For official information, please refer to the NHC and NWS products.

I think this is a done deal as far as where it will go(not that there has been much doubt). It is definitely moving W based on both sat and radar. Unless it gets away from the NE shear soon, it appears that the worst of the weather will probably end up in LA as this moves ashore there tomorrow. I'm not even sure this is going to ramp up anymore. If it can stack some more under the convection we could have a player, but attm it is not happening. I am a rank amateur though, so what do I know?

[Stormcenter]

If this is the case then why do they bother flying into it?

Recon won't be able to provide much additional info for a system that's embedded in a region with more surface obs than any other part of the entire Atlantic Basin. Obs confirm a weak surface low near 28.9N/86.2W. Winds around the low average around 15 kts, though there could be a few 20-25 kt winds in the heavier squalls that are being sheared to the southwest of the low center. Central pressure is about 1011.5mb, give or take a few tenths depending on how well the barometer of the nearby buoy has been calibrated.

What more do you expect to learn from recon today?

http://myweb.cableone.net/nolasue/5f.gif

[KWT]

I suppose given the planes route into the system they actually will learn some more about how condusive the set-up is aloft, I remember NHC has used recon in that way already once this season.

Looks like a weak depression to me right now.

[Dean4Storms]

Looks like it is drifting due west to me now.

[Dean4Storms]

Just too much shear, the center of the low is at the NE extent of the convection with the MLC off to the SW inside the convection easily seen on radar. I don't see it improving much today and this is going to struggle to make TS status as long as the shear continues.

[Aric Dunn]

Looks like it is drifting due west to me now.

if you go back a look at some of the previous best tracks as well as wxman57's as well as my position estimate from last night.. the circulation has not moved much at all in about 8 hours... its basically in the same spot from 8 hours ago. It should eventually begin to move in the general west direction but a short term wsw motion would not be out of the question.

[KWT]

Radar certainly makes it look like its moving westwards right now though Aric I have to admit.

Still it probably is a depression right now, at least given the fact its in the Gulf, the sheared presentation makes it quite obvious really.

[wxman57]

If this is the case then why do they bother flying into it?

Recon won't be able to provide much additional info for a system that's embedded in a region with more surface obs than any other part of the entire Atlantic Basin. Obs confirm a weak surface low near 28.9N/86.2W. Winds around the low average around 15 kts, though there could be a few 20-25 kt winds in the heavier squalls that are being sheared to the southwest of the low center. Central pressure is about 1011.5mb, give or take a few tenths depending on how well the barometer of the nearby buoy has been calibrated.

What more do you expect to learn from recon today?

http://myweb.cableone.net/nolasue/5f.gif

That's their job, to fly when they're told to. There's a slight chance that something semi-dramatic could occur this afternoon with the low center, like maybe it'll tighten up more and the pressure could fall in a small area not picked up on by the surrounding surface obs. Of course, we'd probably be able to pick up on that with high-res satellite imagery.

[Aric Dunn]

Radar certainly makes it look like its moving westwards right now though Aric I have to admit.

Still it probably is a depression right now, at least given the fact its in the Gulf, the sheared presentation makes it quite obvious really.

well thats because all the convection is being blown to the west giving that appearance... Im not going to say that its not drifting around but I see no definite direction over the last few hours

[cycloneye]

Just too much shear, the center of the low is at the NE extent of the convection with the MLC off to the SW inside the convection easily seen on radar. I don't see it improving much today and this is going to struggle to make TS status as long as the shear continues.

I thought it had ideal conditions as it was discussed earlier in this thread.

[BigA]

Is there a realistic chance that the MLC, farther to the SW and closer to the upper level high, could come to dominate, or is this scenario not worth considering?

[Stormcenter]

Not that I want to beat a dead horse on this but ex-TD5 is looking
better as time goes by. Yes it's dealing with shear (again) but it's still organizing
and sustaining very deep convection. It won't take much to get it over
the hump. IMO


http://www.rap.ucar.edu/weather/satelli ... uration=12

[wxman57]

Just too much shear, the center of the low is at the NE extent of the convection with the MLC off to the SW inside the convection easily seen on radar. I don't see it improving much today and this is going to struggle to make TS status as long as the shear continues.

I thought it had ideal conditions as it was discussed earlier in this thread.

The ridge shifted too far to the northwest, cycloneye. The low center is on the far SE side of the ridge, resulting in shear. But I don't think the shear is strong enough to prevent it from becoming a TD and quite possibly a weak TS by landfall. That's about it, though.

[Sanibel]

Good AVN appearance despite the shear.

[MGC]

Looks like a sheared naked low to me....but, there is always a chance that some convection could pop near the center thus warenting an upgrade....MGC

[Dean4Storms]

Just too much shear, the center of the low is at the NE extent of the convection with the MLC off to the SW inside the convection easily seen on radar. I don't see it improving much today and this is going to struggle to make TS status as long as the shear continues.

I thought it had ideal conditions as it was discussed earlier in this thread.

There is less shear to the west near the LA coast, it could organize more quickly once it gets a bit further west. But the ridge is not centered over it and is back further to the NW than what I was expecting.