ATL: DEBBY - Post-Tropical

[Kingarabian]

GFS +24 18z

Kind of stalling right beneath the panhandle.

[Portastorm]

I'm a complete noob at this, but can someone explain how in less than 24 hours the center of circulation is nowhere near where the original cone was?

[img]Image

The NHC was following the Euro's solution, but it never became concrete.

I believe the most plausible reason is the center of circulation kept re-forming more and more to the northeast as the initial identification of a center with the first advisory (yesterday at 4 pm) was the central point of a number of smaller vortices. This isn't a case where there was a clear-cut center of a storm and it just booked it northeast over 24 hours.

[vaffie]

Forecasting two things in the tropics are particularly hard, even with the best models--shear and intensification rates. Shear-induced center reformation is what did this one in. It has played a major role in forecasting errors for numerous other hurricanes that I've studied.

[Portastorm]

Tons of flooded streets, as evidenced by tall the of youtube and fb videos being uploaded.

If you've got any good links per what you mention above, post 'em in the Debby preps/obs thread!

[USTropics]

Florida Highway Patrol's web site will have some information on major road closures:

http://www.flhsmv.gov/fhp/traffic/

Some scattered reports of trees blocking roadways and there's standing water on I-75 in Alachua County among other reports.

Navarre Beach causeway between Pensacola Beach and Navarre Beach is now closed because of flooding, which is to be expected in these conditions.

I can also confirm that parts of US-19 are shut down and traffic is being diverted through alternate roots. Particularly near Tampa road in Palm Harbor and between Curlew road and Countryside blvd in Clearwater.

Images of flooded U.S. 19:
http://img256.imageshack.us/img256/2946/img0042nk.jpg
http://img18.imageshack.us/img18/1503/img0047st.jpg

(note: the particular person in the white car decided to try and brave it instead of getting over to the left hand turn lane and ended up having to push his car out of the water)

[bqhurricane]

I see. I'd always heard that models have a helluva time with storms that are forming, but didn't realize the center of circulation could reform so many times.

[Kingarabian]

+39 hours we have landfall. Sure is taking it's sweet time. Some serious flooding in store for Florida...

[vaffie]

Keep in mind that the 6 and 18z models are generally continuation models. The GFS 0Z and 12Z ones start from scratch and are more important.

[ROCK]

Forecasting two things in the tropics are particularly hard, even with the best models--shear and intensification rates. Shear-induced center reformation is what did this one in. It has played a major role in forecasting errors for numerous other hurricanes that I've studied.

exactly.....we werent the only one fooled. Many METS had the west rack including the NHC. Albeit for about 12 hours....to be fair, I more organized system would have taken the west route. Never could get its act together even now it looks ugly. and for the record, I still would take the EURO over the GFS 9 times out of 10..... that should be no surprise to anyone.

[Kingarabian]

+48hrs
Still on shore. Damn.

[Kingarabian]

Keep in mind that the 6 and 18z models are generally continuation models. The GFS 0Z and 12Z ones start from scratch and are more important.

Oh okay thanks. Yeah I just wait till the 48 hours finishes.

[yzerfan]

How many times does emergency management have to chant 'turn around; don't drown' before it sticks.

TWC has mentioned that the old St. George Island bridge that partially collapsed is, like many old Florida bridges, decomissioned as a road and currently in use as a fishing pier.

[USTropics]

Also here is projected total rainfall amount so far

:

[FutureEM]

Tons of flooded streets, as evidenced by tall the of youtube and fb videos being uploaded.

If you've got any good links per what you mention above, post 'em in the Debby preps/obs thread!

I did

[brunota2003]

I see. I'd always heard that models have a helluva time with storms that are forming, but didn't realize the center of circulation could reform so many times.

Well, it is much similar to a tornado that bounces around. You got the main, "large" circulation (mesocyclone/wall cloud) that continues on, but the tornado itself bounces up and down and changes spots in relate to the storm's base. Weaker tropical cyclones can do something similar...you have the "main circulation", but the spots with a well defined wind shift change places within the broader circulation as convection moves about. One forms and tightens up near the convection, as another rotates out and starts to weaken. Eventually, that makes the entire circulation readjust toward the convection, as each wind shift becomes the dominant feature, and alters the way inflow is flowing into it.

Likewise, because there is wind shear, each new convective cell the storm produces is blow off of/away from the center of circulation, causing the weak LLC to play "catch up" in that particular direction. Without the convection, it dies...without it, the convection dies/isn't organized.

[thetruesms]

The NHC bit on one solution, and the other turned out to be closer to the truth. The cone represents where the center will be 66% of the time. The other 34% of the time the center goes out of the cone. Obviously, though, that 34% is usually further along the track (Day 4 or 5) than this time's.

Actually, the size of the cone is set so that the percentage is the same at all time steps.

[Peach]

General question from someone who is only an avid weather watcher: Is Debbie an 'average' size tropical storm? The NHC listed size, and the book info I have from books indicates she is not large. Is the fact she is in the gulf what makes her seem large to me?

[Portastorm]

Tons of flooded streets, as evidenced by tall the of youtube and fb videos being uploaded.

If you've got any good links per what you mention above, post 'em in the Debby preps/obs thread!

I did

Thank you ... some interesting vids there. Florida deluge indeed!

[tropicwatch]

I lay down for a nap and wake up, holy tidle changes batman. I did not expect to see that much of a change in the forecast cone. Although I knew it was a possibility.

[jdray]

Wow if the 18z GFS verifies, there could be some seriously huge issues with flooding for a lot of Florida. There are spots still not dry from Beryl and the stalled fronts right after her, and Debby looks to want to dump some more on us.