Tropical Depression in Oklahoma

[Donald Giuliano]

Figured I'd start a thread about the system that's been meandering around Oklahoma the last few days. This morning's (June 27) upper air data shows the system has become fully warm-core, and the tropical nature of it can be seen especially well in today's satellite loops--the water vapor and visible being particularly revealing. It even looks as though the trough over the Northern Plains/Great Lakes is serving to enhance the outflow on this system, which appears to currently be intensifying. Tonight could be pretty interesting for those of us in OK. Don't think NHC will be issuing any advisories on this system, but in my opinion it fits the AMS definition of a tropical cyclone.

 

[Jim Leonard]

Sometime during the summer season these type of systems will move into the GOM or the atlantic will quickly become tropical depressions and even tropical storms. The reason is these systems have time to become warm core because of the persistant convection near the low center. Early August 1988 a large cloud cluster like the above mentioned system drifted just off the coast of Louisiana and became tropical storm Beryl.
Sometimes a smaller mcs will drift over the warm ocean and will even develop into a hurricane, good examples Hurricane Alicia August 1983, hurricane Danny 1997.

 

[Brandon Goforth]

No joke, this thing has been flooding parts of OK for over a week, and it doesn't look like it's leaving anytime real soon.

 

[Greg Stumpf]

...in my opinion it fits the AMS definition of a tropical cyclone.

Where's the wind?

 

[Glen Romine]

The AMS definition is a bit sloppy - but doesn't give a minimum wind to qualify as a tropical depression (which is a class of tropical cyclone). However, it does require that the cyclone originate over a tropical ocean - which has been missing over Oklahoma for quite a while. Of course, with all the rain there lately, it may seem like a tropical ocean there. The system doesn't appear to be strongly warm core at midlevels, and the upper level high is offset a bit east of the low level circulation, but it is meteorologically interesting nonetheless.

 

[Doug Lee]

This low has been around in some form for a couple of weeks. I wish it would go away. I haven't been able to mow my lawn as often as I need to. I also do not like to slosh my way across my front yard to get the morning paper!

 

[Jeff Snyder]

It's been kind of wet lately... Too bad the OKC airport hasn't gotten some of the totals that some nearby towns have (e.g. Walters, Seminole, etc). At least we're now "record wet":

[FONT=lucida sans typewriter, lucida console, courier]..RECORD BROKEN FOR CONSECUTIVE NUMBER OF RAINY DAYS AT OKC

THE 0.01 INCHES OF PRECIPITATION RECORDED AT WILL ROGERS WORLD
AIRPORT SO FAR TODAY MARKS THE 15TH CONSECUTIVE DAY WITH AT LEAST A
TRACE OR MORE OF RAINFALL.[/FONT]

[FONT=lucida sans typewriter, lucida console, courier]
See http://kamala.cod.edu/offs/KOUN/0706272204.nous44.html for the remainder of the PNS.

I really need to get some yard work done, but the ground has been too soggy for the past 10 days to do much. Oy!
[/FONT]

 

[Donald Giuliano]

Where's the wind?

The lack of strong surface winds is a defining characteristic of a tropical depression.

The AMS definition is a bit sloppy - but doesn't give a minimum wind to qualify as a tropical depression (which is a class of tropical cyclone). However, it does require that the cyclone originate over a tropical ocean - which has been missing over Oklahoma for quite a while. Of course, with all the rain there lately, it may seem like a tropical ocean there. The system doesn't appear to be strongly warm core at midlevels, and the upper level high is offset a bit east of the low level circulation, but it is meteorologically interesting nonetheless.

From the AMS Glossary, emphasis mine:

"In general, they form over the tropical oceans (except the South Atlantic and the eastern South Pacific) and affect the eastern and equatorward portions of the continents."

Also, the fact that the upper ridge is not perfectly aligned with the surface features is unsurprising, as this is common with weak tropical cyclones.

Just looking at the Southern and Central Plains wind profilers this evening is very interesting...the vertical structure of this low is identical to a purely warm-core landfalling tropical system, despite the fact it formed over land. We're not talking about something that's impossible here (a weak tropical cyclone forming/maintaining itself over land), just highly anomalous.

 

[Greg Stumpf]

The lack of strong surface winds is a defining characteristic of a tropical depression.

I was originally refering to a tropical cyclone.

I was "learned" that a tropical cyclone was a warm core storm that had reached TS status. But apparently, the official definition says otherwise, and cyclones include depressions, so therefore, I stand corrected.

 

[Glen Romine]

"In general, they form over the tropical oceans (except the South Atlantic and the eastern South Pacific) and affect the eastern and equatorward portions of the continents."

Also, the fact that the upper ridge is not perfectly aligned with the surface features is unsurprising, as this is common with weak tropical cyclones.

Selective quoting doesn't make your argument much stronger. I agree the system shows mid-level warm core characteristics, but so are polar lows, occasional MCV's. Most defintions of tropical cyclones are simpler. For instance the JTWC (an often cited resource) simply uses:

"Tropical Cyclone: General term for a non-frontal low-pressure system, developing over tropical or subtropical waters, and having a definite organized circulation."


Note that 'warm core' is not a requirement, just that the system is not baroclinic nor over land or cold waters.

 

[cdcollura]

I think this is an MCV ... Convective-induced vortex.

Tropical cyclones are TYPES of convective vortices, just really strong ones.

MCV's are often warm core as well. Normally these are not very strong wind wise, but banding / cyclonic motion can be discerned in radar imagery.

SPC has some great information about these little "swirls" as well...

http://www.spc.noaa.gov/coolimg/radvort.htm

 

[Donald Giuliano]

Selective quoting doesn't make your argument much stronger. I agree the system shows mid-level warm core characteristics, but so are polar lows, occasional MCV's. Most defintions of tropical cyclones are simpler. For instance the JTWC (an often cited resource) simply uses:

"Tropical Cyclone: General term for a non-frontal low-pressure system, developing over tropical or subtropical waters, and having a definite organized circulation."


Note that 'warm core' is not a requirement, just that the system is not baroclinic nor over land or cold waters.

If one defines a tropical cyclone as one originating over water, then obviously this system cannot be a tropical cyclone. That's not the point I'm trying to make, so please forgive me if I've diverted the conversation.

The point I am trying to make is that the structure of this low is fully consistent with tropical cyclones originating over water. IIRC, this system is a holdover from last week's MCS, a not uncommon scenario other than that it is unusual for a remnant MCV to persist so long (10 days now). During that time, the MCV has grown significantly (well past the mesoscale, so that technically it's no longer a MCV) and acquired fully "tropical" characteristics. Whatever we decide to call it, this system physically differs not at all from a tropical depression originating over water, so I see no reason to differentiate between the two.

 

[Jeff Snyder]

IIRC, this system is a holdover from last week's MCS, a not uncommon scenario other than that it is unusual for a remnant MCV to persist so long (10 days now). During that time, the MCV has grown significantly (well past the mesoscale, so that technically it's no longer a MCV) and acquired fully "tropical" characteristics. Whatever we decide to call it, this system physically differs not at all from a tropical depression originating over water, so I see no reason to differentiate between the two.

So, this is really a warm-core, tropical SCV (synoptic-scale convective vortex), not much unlike a tropical depression, as you note. The visible and water vapor sat imagery yesterday even seemed to show a sort of upper-level anticylcone over the southern Plains, with the typical "scalloped" outflow in two channels to the north and south of the mid-level cyclone.

I had to chuckle the other day when someone I was talking to said "You guys are good... It was supposed to be dry this week, wasn't it"? I tried to explain the fact that the vast majority of the reason why we've seen flooding rains the past 10 days is the extremely intense MCS that rolled through KS/OK/TX last week. No doubt, the large amount of latent heating from extreme vertical mass flux courtesy of 4000-7500 j/kg CAPE over a large area helped to create this mid-level low that has plauged the area for a while now. And to think -- if we had seen a cap bust that day, there'd be a good chance that we'd be dry and hot now.

 

[Tim Vasquez]

This is a great discussion.... just this morning I was trying to figure out why we've had such persistent upper-level troughiness across Texas and Oklahoma, and whether it fits the criteria of a TUTT trough. I haven't yet looked at enough charts to figure out what is driving this thing. If the GFS is any indication, it will be sticking around at least until July 4th and then get shunted down into northern Mexico.

Tim

 

[Tim Vasquez]

Having had a chance to look at more charts, it appears to be more of a baroclinic system, as it seems to exhibit vertical tilt and there's plenty of northerly winds in the high plains region. I wonder why this thing has not been picked up by the prevailing westerlies though.

Tim