ATL: DON - Remnant - Discussion

[SunnyThoughts]

What does it mean when people refer to the recon data as flagged or unflagged?

If its flagged, that means its an unreliable reading.. unflagged, of course would be a reliable reading.

[KWT]

Shear wasn't forecast to be this strong in the Gulf. SHIPS really changed its forecast last night. Previously was forecasting shear to be less than 10 knots.

I think they obviously must have missed the shear, the analysis also was rather too low. i suspect mid level shear is higher then was shown...mind you I think the globals did notice the shear, hence why they didn't strengthen much.

[SouthDadeFish]

What does it mean when people refer to the recon data as flagged or unflagged?

Flagged data is what occurs when there are high rain-rates, that often obscure the true wind reading. The rain doesn't always allow an accurate reading to be taken with the microwave instruments and as a result, the data that does come in these situations is "flagged."

[Stormcenter]

It seems as though shear has been an ongoing issue for tropical systems in the GOM since last hurricane season and even before that. I'm NOT complaining.

Looks like the shear wins over hurricane burst expectations. I don't know where people were getting those "near perfect conditions in the Gulf" quotes. TWC was right. Shear in the Gulf should hamper development (unless it abates).

[nicole]

is shear expected to subside or maintain??? Or do we know..

[KWT]

nicole, the shear is expected to remain, should prevent it from strengthening into a hurricane, though I still expect a strong TS providing it doesn't get totally wiped out by the shear of course!

[Lane]

Thank you SouthDadeFish and SunnyThoughts for the info.

[Dave]

[SouthDadeFish]

Shear wasn't forecast to be this strong in the Gulf. SHIPS really changed its forecast last night. Previously was forecasting shear to be less than 10 knots.

I think they obviously must have missed the shear, the analysis also was rather too low. i suspect mid level shear is higher then was shown...mind you I think the globals did notice the shear, hence why they didn't strengthen much.

Well I do believe SHIPS runs off of GFS upper-level forecasts. GFS was showing a relatively favorable environment in the Gulf until last night. Here is the forecast from the 25th 6Z run:



That shows relatively light upper-level winds.

[Sanibel]

Sometimes there tends to be a "stage-clearer" like Bonnie in 2004 followed by a better developed system. I thought Don was going to muscle-up. Anyway, I fear this won't deliver much moisture.

[KWT]

SDF, indeed but then again the type of shear that really tends to knock the stuffing out off systems is mid level shear and is often the type the models don't tend to handle as well from experience.

[Dave]

350
URNT15 KNHC 281607
AF303 0204A DON HDOB 37 20110728
155800 2354N 09042W 8431 01562 0093 +175 +048 324014 014 /// /// 03
155830 2353N 09043W 8432 01562 0094 +175 +050 328015 015 /// /// 03
155900 2352N 09044W 8425 01568 0095 +175 +052 330016 017 /// /// 03
155930 2350N 09046W 8433 01561 0094 +173 +054 330014 014 /// /// 03
160000 2349N 09047W 8430 01566 0097 +171 +057 326012 012 /// /// 03
160030 2348N 09048W 8429 01566 0094 +175 +058 321013 014 /// /// 03
160100 2347N 09049W 8433 01563 0096 +173 +059 319014 015 /// /// 03
160130 2346N 09051W 8428 01569 0098 +171 +059 323015 016 /// /// 03
160200 2345N 09052W 8429 01566 0098 +171 +059 326016 017 /// /// 03
160230 2344N 09053W 8432 01566 0099 +173 +059 324014 015 /// /// 03
160300 2342N 09054W 8429 01568 0100 +170 +058 326014 014 /// /// 03
160330 2341N 09056W 8433 01567 0101 +170 +058 321014 015 /// /// 03
160400 2340N 09057W 8429 01571 0101 +172 +058 320014 014 /// /// 03
160430 2339N 09058W 8430 01571 0102 +170 +057 320015 018 /// /// 03
160500 2338N 09059W 8440 01561 0104 +167 +057 320013 014 /// /// 03
160530 2337N 09101W 8425 01574 0103 +169 +056 318014 015 /// /// 03
160600 2336N 09102W 8426 01572 0102 +170 +055 324014 015 /// /// 03
160630 2334N 09103W 8432 01568 0103 +170 +056 325014 015 /// /// 03
160700 2333N 09104W 8427 01574 0106 +167 +056 319013 014 /// /// 03
160730 2332N 09106W 8433 01568 0104 +170 +056 321013 013 /// /// 03
$$
;

[Sambucol]

North of Corpus IMO...closer to matagorda and or San Luis pass...

What happened? I thought this one was going in south of Corpus? Does this northern track change indicate a trend or a one time thing?

[SouthDadeFish]

I think what the GFS got wrong was the ULL that is moving across Florida. It is really pinching Don, and bringing that northerly wind over him. In the image above the GFS doesn't really depict it.

[wxman57]

Note that the SHIPS model looks over a very large area when computing possible wind shear in Don's path. Often this area extends well beyond the circulation of a small storm like Don. So if the wind shear is actually well north of a small storm, the smaller storm might not be impacted as much or at all by the shear. I think it's certainly possible Don could become a hurricane just prior to landfall, but it won't be any "Ike". Hurricane force winds may cover only a very tiny area near the center.

[ozonepete]

Well I do believe SHIPS runs off of GFS upper-level forecasts. GFS was showing a relatively favorable environment in the Gulf until last night. Here is the forecast from the 25th 6Z run:



That shows relatively light upper-level winds.

That's a 200mb level forecast. Need to see shear from low to mid/upper levels.

[JonathanBelles]

Tropical Storm Don is not well stacked and is partially exposed, but conditions are looking better. Don is also up to 50 mph (with recon information, my estimate):

http://wp.me/p1xnuB-3B

[KWT]

Note that the SHIPS model looks over a very large area when computing possible wind shear in Don's path. Often this area extends well beyond the circulation of a small storm like Don. So if the wind shear is actually well north of a small storm, the smaller storm might not be impacted as much or at all by the shear. I think it's certainly possible Don could become a hurricane just prior to landfall, but it won't be any "Ike". Hurricane force winds may cover only a very tiny area near the center.

Interesting that you still think this has a shot at becoming a hurricane...I'm personally now not convinced the shear will ever allow for more then say 55kts. what I will say is there is still plenty enough time for it to develop into a hurricane if the shear was to ease off at all.

Slow but steady strengthening is in order right now, might have to watch how the convection handles the enxt few hours, could just as easily see the whole convective mass poof in the next couple of hours, its getting that look a system gets before it blows off the convection and gets ready to blow up another region.

[SouthDadeFish]

SDF, indeed but then again the type of shear that really tends to knock the stuffing out off systems is mid level shear and is often the type the models don't tend to handle as well from experience.

Not much mid-level shear:



I don't see much either on the 12Z GFS initialization at the 250mb or 300mb level.

[SouthDadeFish]

That's a 200mb level forecast. Need to see shear from low to mid/upper levels.

I was showing that because it was in agreement with the 850mb winds at the time. I was assuming there wasn't much mid-level shear.