Tornado Watch

[HAltschule]

Tornado Watch now being issued for Louisiana to the Florida Panhandle. Doppler indicated tornado already being warned near MOB as we speak. Good directional shear looks to be producing nice low level rotation in the cells already coming onshore with the initial feeder bands. Plenty of instability with the shear will mean some Tornadoes this evening and overnight. Anyone remember the outbreak of "Beryl" when TOR's formed well ahead of the center b/c of instability and shear. Hopefully most folks are hunkered down already (not likely) b/c there will probably be some nice storms they run into tonight...way ahead of Katrina herself.

 

[Andrew Khan]

There is also a TORNADO WARNING In Southern AL, issued by the NWS in, Mobile, AL.

 

[Saul Trabal]

What's the strongest a tornado can get from a hurricane thunderhead ? I understand that they usually don't get stronger than F2s.

 

[HAltschule]

There's really no limit as to how strong they can get but they are usually very short lived and usually move very quickly (45-55 mph). Some last year were very destructive!!

 

[Anonymous]

I don't think there is a hypothetical limit but I noticed a lot of the tornado damage due to Hurricanes and tropical storms does not always get a survey. Or sometimes it is not known whether it was due to a tornado. From what I have seen of Hurricane or tropical depression induced tornadoes F2 seems to be usually pretty high up there.

 

[nickgrillo]

Originally posted by Saul Trabal
What's the strongest a tornado can get from a hurricane thunderhead ? I understand that they usually don't get stronger than F2s.

Tornadoes associated with hurricane-spawned storms can be just as violent as with any other tornadic supercell... As there has been numerous hurricanes in the past which have produced VIOLENT tornadoes.

As for today... I would say a few tornadoes are a pretty good possibility. Of course, not sure of the magnitude... But they could certainly be anywhere from weak to strong.

 

[Robert Dewey]

Originally posted by nickgrillo+--><div class='quotetop'>QUOTE(nickgrillo)</div>

<!--QuoteBegin-Saul Trabal

What's the strongest a tornado can get from a hurricane thunderhead ? I understand that they usually don't get stronger than F2s.

Tornadoes associated with hurricane-spawned storms can be just as violent as any other tornadic supercell... As there has been numerous hurricanes in the past which have produced VIOLENT tornadoes.

As for today... I would say a few tornadoes are a pretty good possibility. Of course, not sure of the magnitude... But they could certainly be anywhere from weak to strong.[/b]

Yeah, some of those cells in that band look pretty strong - nothing supercellular at the moment though. Low level helicity will be increasing quite a bit, by the minute even, and with good SFC based instability, the threat for tornadoes seems relatively high compared to other tropical cyclones.

 

[Anonymous]

Tropical cyclone tornadoes tend to be relatively weak and short-lived, occurring in a paradigm not unlike that of low-topped supercell tornadoes (high shear, relatively low instability environments). Their mesocyclones tend to be quite small and transient on doppler velocity imagery, spinning up and dying out quickly.

We had a couple of tornadoes from the remnants of TS Arlene in June, and it was a very interesting night. The circulations, as described above, were very small and transient, and made for little decision-making time before pulling the trigger on a warning.

 

[Andrew Khan]

Their is a possibility however, that later on when the storm moves in more, that their could be some violent tornadoes. Aren't the tornadoes in Hurricanes generally spawned from "Embedded Supercells"? I'd say, they could get very strong and no limit, really. Why are they short lived?

 

[Joe Nield]

Forgot to sign in...

Tropical cyclone tornadoes tend to be relatively weak and short-lived, occurring in a paradigm not unlike that of low-topped supercell tornadoes (high shear, relatively low instability environments). Their mesocyclones tend to be quite small and transient on doppler velocity imagery, spinning up and dying out quickly.

We had a couple of tornadoes from the remnants of TS Arlene in June, and it was a very interesting night. The circulations, as described above, were very small and transient, and made for little decision-making time before pulling the trigger on a warning.

And to add to this...

Good luck picking out tornado damage after this is all said and done though. That would make for an interesting survey.

 

[Guest]

The local weather guys on WWL-TV in New Orleans have been saying that the NWS is going to issue tornado warnings that parallel the path of the eyewall due to the intense speed of the storm. I've never heard of this before. Anyone know what this is about?

 

[nickgrillo]

Originally posted by rdewey+--><div class='quotetop'>QUOTE(rdewey)</div>

Originally posted by nickgrillo@
<!--QuoteBegin-Saul Trabal

What's the strongest a tornado can get from a hurricane thunderhead ? I understand that they usually don't get stronger than F2s.

Tornadoes associated with hurricane-spawned storms can be just as violent as any other tornadic supercell... As there has been numerous hurricanes in the past which have produced VIOLENT tornadoes.

As for today... I would say a few tornadoes are a pretty good possibility. Of course, not sure of the magnitude... But they could certainly be anywhere from weak to strong.

Yeah, some of those cells in that band look pretty strong - nothing supercellular at the moment though. Low level helicity will be increasing quite a bit, by the minute even, and with good SFC based instability, the threat for tornadoes seems relatively high compared to other tropical cyclones.[/b]

No kidding... Checking mesoanaly which shows >200 0-1KM SRH and >2000J/KG sbCAPE along the coast (and increasing rapidly). I'm going to take a wild guess and say that there should be a good dozen tornadoes reported along the coast through today...

 

[Andrew Khan]

Wow, that would be tough figuring out what is tornado damage and what is not, lol. How are the conditions for today favorable for tornadoes?

 

[nickgrillo]

Originally posted by Andrew Khan
Wow, that would be tough figuring out what is tornado damage and what is not, lol. How are the conditions for today favorable for tornadoes?

Like I said above, pretty good. To make it short, strong low-level shear in the wake of the outer band of Katrina moving onshore, along with strong SFC-based instability (sbCAPE >2000J/KG along the coast and increasing) and excellent vertical shear profiles make a very good setup for widespread low-topped supercells to develop through this afternoon and evening (and continuing into the night) with the potential for quite a few tornadoes.

 

[Jason_Politte]

Originally posted by Guest
The local weather guys on WWL-TV in New Orleans have been saying that the NWS is going to issue tornado warnings that parallel the path of the eyewall due to the intense speed of the storm. I've never heard of this before. Anyone know what this is about?

Many offices that have had to deal with hurricanes in recent years have been doing this basically because there is no such warning to actually warn for the eyewall. I doubt if issuing tornado warnings for the eyewall has much effect though or does any good considering that many won't have access to the warning or will already be taking shelter because of the hurricane strength winds already ongoing.

Edit: I'll also add that because this storm will be making landfall quite a bit earlier than originally expected, this technique may actually have some use during this event . . . if those affected can receive the warning.

Jason