Post Tropical Cyclone Debby

[phil882]

Assuming the western track verifies closer to the ECMWF operational and ensemble runs, Debby should remain under significant shear until Monday. Afterwards, the ECMWF has the upper low cutting off and becoming smaller in scale, likely in response to the diabatic heating and outflow from Debby's convection. This should allow the upper level westerly wind component around Debby to diminish, resulting in a reduction of the shear. Therefore, I don't expect much, if any, intensification until sometime on Monday, at which point we'll probably see a reorganization of Debby's convective pattern into something that looks more symmetric. Then the intensification rate should increase on Tuesday.

I think the environmental conditions are good enough for this to become a hurricane, honestly.

I think we are in agreement here. The assumption is a big one however, and I'm not entirely sold on the westward track quite yet. The ECMWF is assuming the current llc continues to drift northwestward for the next 24 hours. The convective pattern currently would tend to favor possible eastward relocations if the convection is able to remain decently strong. The track is strongly sensitive to where Debby moves over the first 24 hours, and any eastward relocations could cause a substancial shift rightward in the model guidance.

[phil882]

I can't remember... but does anyone know if they made the GFS-enkf from last year the GFS op this year, or am I imagining things? If not, what is the best source for that model?

If I remember correctly, the GFS-enkf was more reliable than the GFS operational last year.

Yes the GFS-enkf is now operational.

[CUmet]

I disagree with the following statement. Mesovorticies are important to the structure of a TC because the dominant mesovorticies can influence the motion and intensity of a tropical cyclone. A good example is Claudette in 2003. The system had multiple mesovoritices that were rotating around a mean center. When each mesovortex interacted with the convection, it often resulted in Claudette taking a jog to the right of the mean track, with a corresponding drop in the pressure. Some excerpts from the NHC discussions reveal this.

Sounds like typical downshear center reformation to me, which I'm sure we'll see with this storm. You could say that the mesovortices enhance this process when they re-enter the convection and move towards the best updrafts, which would supercharge the mesovortex and make it the deepest pressure minima in the storm (and thus move the storm center towards the convection). However, the driving process is environmental wind shear which is displacing convection from the center imo, not the mesovortices.

I think there are elements of truth to both of these posts. As long as you have the strong shear, you'll have periodic center reformations or center drifts towards the convection, which will result in short-term intensity changes. Often times in these cases, however, it's only a matter of time before the convection gets dislocated from the center again, and the cycle repeats itself over and over. So, the storm over this cycle really hasn't changed much structurally-speaking.

However, in this case, since the convection is displaced towards the east, and the main uncertainty regarding the track is oriented in a west-east plane, center reformations under the convection to the east could be very important to the track of Debby.

[dan88]

With regards to mesovorticies recon is current closely investigating one from 850MB (recon has climbed after going through convection earlier) located NE of the current center location, at roughly 26.9N, 86.7W, along the Western edge of the convection

212730 2658N 08639W 8428 01512 //// +196 //// 048009 011 000 003 05
212800 2657N 08640W 8422 01521 //// +187 //// 345005 009 /// /// 05
212830 2655N 08639W 8436 01507 //// +184 //// 311005 006 000 003 05
212900 2654N 08638W 8426 01516 //// +187 //// 202001 004 000 002 05
212930 2653N 08637W 8430 01511 //// +181 //// 262005 007 /// /// 05
213000 2651N 08635W 8430 01512 //// +181 //// 260007 008 /// /// 05
213030 2650N 08634W 8430 01510 //// +182 //// 267008 009 000 002 05
213100 2649N 08633W 8428 01514 //// +183 //// 244011 012 000 003 05
213130 2647N 08632W 8430 01510 //// +177 //// 224014 015 004 003 05
213200 2646N 08631W 8428 01514 //// +180 //// 224016 017 001 004 05
213230 2645N 08630W 8426 01515 //// +175 //// 227019 020 002 004 01
213300 2644N 08628W 8429 01512 //// +175 //// 224020 021 003 003 05
213330 2642N 08627W 8430 01511 //// +175 //// 225022 023 000 005 05
213400 2642N 08626W 8418 01528 //// +175 //// 221021 022 /// /// 05
213430 2643N 08625W 8430 01510 //// +176 //// 216019 021 000 003 01
213500 2645N 08626W 8432 01507 //// +177 //// 220016 017 001 003 05
213530 2646N 08628W 8430 01511 //// +182 //// 220016 017 001 003 01
213600 2647N 08629W 8425 01515 //// +179 //// 217016 017 001 003 05
213630 2648N 08630W 8429 01511 //// +180 //// 222011 014 001 004 05
213700 2649N 08632W 8431 01509 //// +180 //// 253007 009 002 003 05
213730 2650N 08633W 8427 01513 //// +185 //// 256006 008 000 004 05
213800 2651N 08634W 8433 01508 //// +182 //// 263005 005 /// /// 05
213830 2653N 08635W 8425 01515 //// +185 //// 238005 006 000 002 05

[phil882]

Sounds like typical downshear center reformation to me, which I'm sure we'll see with this storm. You could say that the mesovortices enhance this process when they re-enter the convection and move towards the best updrafts, which would supercharge the mesovortex and make it the deepest pressure minima in the storm (and thus move the storm center towards the convection). However, the driving process is environmental wind shear which is displacing convection from the center imo, not the mesovortices.

Yes environmental wind shear is the driving mechanism for center reformation. My point is that its easier to have center relocations when you have a broad and diffuse center such as this with multiple mesovorticies rotating around. Seems like we are in agreement after all. Thus if can be important to pay attention to where the vorticity seems to be aggregating, as this could signal a new mean center relocation.

[Superstorm93]

With regards to mesovorticies recon is current closely investigating one from 850MB (recon has climbed after going through convection earlier) located NE of the current center location, at roughly 26.9N, 86.7W, along the Western edge of the convection

212730 2658N 08639W 8428 01512 //// +196 //// 048009 011 000 003 05
212800 2657N 08640W 8422 01521 //// +187 //// 345005 009 /// /// 05
212830 2655N 08639W 8436 01507 //// +184 //// 311005 006 000 003 05
212900 2654N 08638W 8426 01516 //// +187 //// 202001 004 000 002 05
212930 2653N 08637W 8430 01511 //// +181 //// 262005 007 /// /// 05
213000 2651N 08635W 8430 01512 //// +181 //// 260007 008 /// /// 05
213030 2650N 08634W 8430 01510 //// +182 //// 267008 009 000 002 05
213100 2649N 08633W 8428 01514 //// +183 //// 244011 012 000 003 05
213130 2647N 08632W 8430 01510 //// +177 //// 224014 015 004 003 05
213200 2646N 08631W 8428 01514 //// +180 //// 224016 017 001 004 05
213230 2645N 08630W 8426 01515 //// +175 //// 227019 020 002 004 01
213300 2644N 08628W 8429 01512 //// +175 //// 224020 021 003 003 05
213330 2642N 08627W 8430 01511 //// +175 //// 225022 023 000 005 05
213400 2642N 08626W 8418 01528 //// +175 //// 221021 022 /// /// 05
213430 2643N 08625W 8430 01510 //// +176 //// 216019 021 000 003 01
213500 2645N 08626W 8432 01507 //// +177 //// 220016 017 001 003 05
213530 2646N 08628W 8430 01511 //// +182 //// 220016 017 001 003 01
213600 2647N 08629W 8425 01515 //// +179 //// 217016 017 001 003 05
213630 2648N 08630W 8429 01511 //// +180 //// 222011 014 001 004 05
213700 2649N 08632W 8431 01509 //// +180 //// 253007 009 002 003 05
213730 2650N 08633W 8427 01513 //// +185 //// 256006 008 000 004 05
213800 2651N 08634W 8433 01508 //// +182 //// 263005 005 /// /// 05
213830 2653N 08635W 8425 01515 //// +185 //// 238005 006 000 002 05

[phil882]

To previde some perspective, here is the little vortex in comparison to the center fix the recon made a few hours ago. Were it to become the dominant center, that would be a significant relocation to the northeast.

[turtlehurricane]

Yes environmental wind shear is the driving mechanism for center reformation. My point is that its easier to have center relocations when you have a broad and diffuse center such as this with multiple mesovorticies rotating around. Seems like we are in agreement after all. Thus if can be important to pay attention to where the vorticity seems to be aggregating, as this could signal a new mean center relocation.

Funny that just as we're talking about this recon finds a new center 110 miles NE of the other one, can't find sfc pressure values though so don't know if it's dominant in any way.

I think there are elements of truth to both of these posts. As long as you have the strong shear, you'll have periodic center reformations or center drifts towards the convection, which will result in short-term intensity changes. Often times in these cases, however, it's only a matter of time before the convection gets dislocated from the center again, and the cycle repeats itself over and over. So, the storm over this cycle really hasn't changed much structurally-speaking.

However, in this case, since the convection is displaced towards the east, and the main uncertainty regarding the track is oriented in a west-east plane, center reformations under the convection to the east could be very important to the track of Debby.

I agree that center reformations to the east are going to significantly affect the track, which makes it even more surprising the NHC has it going west immediately.

Interesting to watch the exposed mesovortices dance around each other, vigorous little things.

[Alfoman]

so could this mean that there are two lows here that will eventually split like the GFS is advertising?

[Indystorm]

I think the westward track is the most reasonable assumption for now. What scares me in the advisory is that Debby is the earliest 4th storm in the historical record with Dennis in 2005 being the prior record holder. But that is for another discussion.

[Superstorm93]

Tornado in FL associated with Debby

http://youtu.be/ETG2gXY6rfU

[phil882]

Data from the dropsonde in the mesovortex they went through about 10-15 minutes ago has the pressure down to 1001 hPa, so the plot thickens.

[Ian]

good number of tornado warnings in s fl this afternoon

[Superstorm93]

Another mission scheduled for tonight.

. ATLANTIC REQUIREMENTS

1. SUSPECT AREA (GULF OF MEXICO)

FLIGHT ONE -- TEAL 70 --

A. 25/0000Z, 0600Z

B. AFXXX 0304A CYCLONE

C. 23/2245Z

D. 27.5N 88.2W

E. 24/2300Z TO 25/0600Z

F. SFC TO 10,000 FT

[dan88]

Recon is investigating the broad center SW of the mesovortex, centered roughly 26.2N 87.6W (same as the advisory location). While they are not reporting back the extrap pressure, they are flying at roughly 10-12M lower than they were with the same flight pressure, so this is probably a tad deeper than the NE low with pressure, at least judging just off 843MB flight level.

[phil882]

[Mallow]

Nice calamityloop!

[Amped]

Center relocation, and within 3 hrs it's back to the same spot as the old one.

[NavarreDon]

Product: Air Force Vortex Message (URNT12 KNHC)

Transmitted: 23rd day of the month at 22:53Z

Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 302)

Mission Purpose: Investigate first suspect area (flight in the North Atlantic basin)

Mission Number: 1

Observation Number: 14

A. Time of Center Fix: 23rd day of the month at 22:18:40Z

B. Center Fix Coordinates: 26°04'N 87°45'W (26.0667N 87.75W)

B. Center Fix Location: 304 miles (489 km) to the S (186°) from Pensacola, FL, USA.

C. Minimum Height at Standard Level: 1,428m (4,685ft) at 850mb

D. Estimated (by SFMR or visually) Maximum Surface Wind: 48kts (~ 55.2mph)

E. Location of the Estimated Maximum Surface Wind: 109 nautical miles (125 statute miles) to the NE (50°) of center fix

F. Maximum Flight Level Wind Inbound: From 118° at 53kts (From the ESE at ~ 61.0mph)

G. Location of Maximum Flight Level Wind Inbound: 129 nautical miles (148 statute miles) to the NE (50°) of center fix

H. Minimum Sea Level Pressure: 1001mb (29.56 inHg) - Extrapolated

I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 18°C (64°F) at a pressure alt. of 1,524m (5,000ft)

J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 19°C (66°F) at a pressure alt. of 1,525m (5,003ft)

K. Dewpoint Temp (collected at same location as temp inside eye): 16°C (61°F)

K. Sea Surface Temp (collected at same location as temp inside eye): Not Available

L. Eye Character: Not Available

M. Eye Shape: Not Available

N. Fix Determined By: Penetration, Wind, Pressure and Temperature

N. Fix Levels (sfc and flt lvl centers are within 5nm of each other): Surface and 850mb

O. Navigation Fix Accuracy: 0.02 nautical miles

O. Meteorological Accuracy: 10 nautical miles

Remarks Section:

Maximum Flight Level Wind: 61kts (~ 70.2mph) in the north quadrant at 20:20:30Z

Sea Level Pressure Extrapolation From: 850mb

[Superstorm93]

48 knot VDM...

Up to 50 knots at 8pm?

[HurricaneJosh]

Speaking of Claudette 2003, an early-season, W-moving, strong (80-kt) Cat 1 that made landfall near Port O'Connor, TX...

Here's some TWC coverage of that one. It's pretty lame, actually. The crew was perfectly situated at the landfall point, but in typical TWC fashion, the eyewall footage is entirely of Jeff Morrow acting dramatic in front of the camera-- so all you see is him. Was there nothing else to show in the eyewall of an 80-kt hurricane?

I know I'm sounding a little harsh, but storm footage should be about the storm, not the dudes covering it:

[bobbutts]

Nice calamityloop!

it's memorizing.. a few small swirls seem to get consumed by the main one

[Scott747]

18z HWRF -

[HurricaneJosh]

18z HWRF -

Well! At this point, chasing Debby will involve you just chilling out on the sofa as it comes to you.

[Scott747]

Well! At this point, chasing Debby will involve you just chilling out on the sofa as it comes to you.

Yeah there wouldn't be much 'chasing' involved. Unfortunately the Purple Cow wouldn't be an option as Surfside would be under a few feet of water. Would have to base behind the levee.

Seriously though it's good to see that the HWRF so far isn't going bonkers and showing viable options. Miss the porn but it needed to become much more reliable. Trend so far is further N and a bit faster. 0z runs will be interesting.

[Superstorm93]

[Scott747]

18z GFDL has changed and is inline with most of the other models. Approaches Grand Isle before turning W and hugging the coast.

[NavarreDon]

AT 700 PM CDT...0000 UTC...THE CENTER OF TROPICAL STORM DEBBY WAS

LOCATED NEAR LATITUDE 26.1 NORTH...LONGITUDE 87.5 WEST. DEBBY HAS

BEEN NEARLY STATIONARY DURING THE PAST SEVERAL HOURS...AND LITTLE

MOVEMENT IS EXPECTED TONIGHT. A SLOW NORTHWARD MOTION IS FORECAST

TO BEGIN BY SUNDAY MORNING...FOLLOWED BY A GRADUAL WESTWARD TURN BY

SUNDAY NIGHT OR MONDAY MORNING. ON THE FORECAST TRACK...THE CENTER

OF DEBBY WILL BE MOVING OVER THE NORTHERN GULF OF MEXICO DURING THE

NEXT FEW DAYS.

MAXIMUM SUSTAINED WINDS ARE NEAR 50 MPH...85 KM/H...WITH HIGHER

GUSTS. THESE WINDS ARE OCCURRING WELL EAST OF THE CENTER OF

CIRCULATION. SOME STRENGTHENING IS FORECAST DURING THE NEXT 48

HOURS.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 175 MILES...280 KM..

MAINLY NORTHEAST AND EAST OF THE CENTER.

THE MINIMUM CENTRAL PRESSURE ESTIMATED FROM RECONNAISSANCE AIRCRAFT

DATA IS 1000 MB...29.53 INCHES.

[PSUBlizzicane2007]

Yes the GFS-enkf is now operational.

http://www.americanw...lman-filtering/

Interesting! Usually last year, the GFSe was more in line with the ECMWF and therefore more accurate than the GFSo.... but so far with Debby, it couldn't be more opposite.

Hmmm...

[thegreatdr]

The current GFS (old parallel) had problems with Alberto as well. Word on the street is that NHC was not enthused about its implementation, based on the 2011 hurricane season. There is a little more convective feedback, which occasionally contaminates its surface lows.

Interesting! Usually last year, the GFSe was more in line with the ECMWF and therefore more accurate than the GFSo.... but so far with Debby, it couldn't be more opposite.

Hmmm...