ATL: IMELDA - Post-Tropical - Discussion

[jasons2k]

On another note - it's almost surreal - watching the Astros game. Minute Maid park is business-as-usual - hard to believe a Tropical Storm made landfall today in Freeport.

OK, back to it:

Mesoscale Precipitation Discussion 0861
NWS Weather Prediction Center College Park MD
1048 PM EDT Tue Sep 17 2019

Areas affected...Upper Texas Coast and Houston Metro

Concerning...Heavy rainfall...Flash flooding likely

Valid 180247Z - 180847Z

Summary...A potentially significant flash flood event along the
upper Texas coast and Houston metro may setup from late this
evening and overnight. Hourly totals in excess of 2" with totals
through 4 AM CDT 3-6" are likely. Isolated totals through 4 AM CDT
of 6-8" are possible.

Discussion...As of 0230Z, the latest estimated position of TD
Imelda was west/southwest of Houston per recent observations and
radar imagery. Radar shows several training rain bands spiraling
onshore. In the last 6 hours, widespread 2-4" totals have been
observed, from mainly the south Houston metro toward the Galveston
coastal areas and near Freeport. In the last 18-24 hours,
widespread 4-6" totals have been observed with local maxes in the
6-7" range. All of this rain today has primed and conditioned the
soils, resulting in a much lower flash flood guidance.

A potentially significant flash flood event may setup overnight in
and around the Houston metro as the environmental conditions
remain more than sufficient for long duration heavy rain. PWs
analyzed from the 00Z soundings and blended TPW products were 2.2
to 2.4". The most recent mesoanalysis also showed favorable
instability in the region, especially from Houston eastward where
MUCAPE of 2000-2500 J/kg exists. With warm cloud depths well above
4 km, extremely efficient rain producing thunderstorms are
expected. Through the overnight, there will be a narrow axis where
the best moisture convergence overlaps with the favorable
instability and higher PWs, generally east/southeast of the low
center as it drifts north/northeast. This puts the greater Houston
metro area in this axis, further highlighting the potentially
significance.

The most recent hi-res models have a fairly tight cluster of 3-6"
totals through 4 AM CDT with some CAMs showing isolated 8" totals
(high-end scenario). The most recent HREF probabilities show
moderate probabilities of 1-hr totals exceeding 2-3" from around
the Houston area toward the Galveston coast.

All told, the combination of slow-moving TD Imelda with the
extreme environmental conditions for heavy rainfall over a highly
urban area could result in significant flash flood event. This
situation will continue to be monitored through the night.

Taylor

ATTN...WFO...HGX...LCH...

ATTN...RFC...WGRFC...

LAT...LON 30789504 30559466 30189419 29739405 29549433
29379464 29199502 28909539 28669589 29209590
29379555 29949586 30409585 30649566

[jabman98]

wobble and stalling may be an issue with Imelda

Doesn't look like it's stalling. Looks like it's moving north.

[StormLogic]

Gotta Love Nighttime Microphysics

[1900hurricane]

 https://twitter.com/1900hurricane/status/1174160646679728129

[StormLogic]

*wobbles east*

[SoupBone]

Finally starting to actually rain in NW Houston.

[Steve]

Big cold clouds firing off on land to the south. Look for that band to be fairly vicious for a TD. Storms should refire toward morning elsewhere and daytime heating kicks in on land. Probably gonna be a lot of 7-12” but it always looked like tomorrow night into Thursday would be the most rainfall. I guess if it lifts out faster, no so much.

https://www.tropicaltidbits.com/sat/sat ... product=ir

[SoupBone]

Big cold clouds firing off on land to the south. Look for that band to be fairly vicious for a TD. Storms should refire toward morning elsewhere and daytime heating kicks in on land. Probably gonna be a lot of 7-12” but it always looked like tomorrow night into Thursday would be the most rainfall. I guess if it lifts out faster, no so much.

https://www.tropicaltidbits.com/sat/sat ... product=ir

That's the thing, at least for now it's moving much faster. It wasn't supposed to be near Conroe until noon tomorrow, but if it maintains its current pace, it will be well north of there by noon.

[storm_in_a_teacup]

Gotta Love Nighttime Microphysics
https://i.imgur.com/hlpPYCc.jpg

What’s the microphysics involved here exactly?

[Steve]

Big cold clouds firing off on land to the south. Look for that band to be fairly vicious for a TD. Storms should refire toward morning elsewhere and daytime heating kicks in on land. Probably gonna be a lot of 7-12” but it always looked like tomorrow night into Thursday would be the most rainfall. I guess if it lifts out faster, no so much.

https://www.tropicaltidbits.com/sat/sat ... product=ir

That's the thing, at least for now it's moving much faster. It wasn't supposed to be near Conroe until noon tomorrow, but if it maintains its current pace, it will be well north of there by noon.

Bands are still going to flood some people. It just depends if it's more east and north or even to the south on a refire or whatever. Also props out to the RGEM on predicting it would look better on land. IR is pretty cool looking tonight. It would be great to see visible, but it might degrade looks wise by tomorrow.

[Steve]

It looks really cool on the shortwave too if anyone hasn't looked at it in a while.
https://www.tropicaltidbits.com/sat/sat ... t=vis-swir

It's got that look like if it was offshore a day or two and coming up, that people would be getting nervous.

[jabman98]

It looks really cool on the shortwave too if anyone hasn't looked at it in a while.
https://www.tropicaltidbits.com/sat/sat ... t=vis-swir

It's got that look like if it was offshore a day or two and coming up, that people would be getting nervous.

Have to say, I'm nervous now. I guess going through Harvey has left me wary.

[watsx2]

On shortwave it looks to be going more East than North

Sent from my SM-N960U using Tapatalk

[Steve]

It looks really cool on the shortwave too if anyone hasn't looked at it in a while.
https://www.tropicaltidbits.com/sat/sat ... t=vis-swir

It's got that look like if it was offshore a day or two and coming up, that people would be getting nervous.

Have to say, I'm nervous now. I guess going through Harvey has left me wary.

For sure. Always be wary. But hopefully the impacts are going to be more isolated. Next 24-30 hours will come down to how the bands set up. You see one now firing off south of Franklin and New Iberia, but that will probably die off and refire east or west later. Certainly anyone up through Jasper and toward even like Texarkana or Shreveport, you can get stuck under a feeder for hours and and get trapped in a car or whatever. People need to be careful, because though there probably won't be widespread Harvey rainfall totals, there's going to be enough to cause trouble for some people.

[Steve]

There's the white cloud tops on IR.
https://www.tropicaltidbits.com/sat/sat ... product=ir

[StormLogic]

Pretty Sure it looks like SETX is fixing to get dumped on.

[GCANE]

 https://twitter.com/GigEm12_Steph/status/1174272288163848192

[Nederlander]

Pretty stout band setting up over the Golden Triangle. I would not be surprised to some decent totals here (8-10” or more) today.

[bohaiboy]

Lucky drive from house to office (6 miles - I610/59) Wipers on intermittently , did not have to use umbrella to the car or from garage to office in downtown. Traffic normal, but I think I just beat the southern edge by a few minutes. No water pooling on roads that i could see, overall no worse than any Houston commute during a thunderstorm.

[sphelps8681]

I have to drive to Beaumont today for drs appt. Might need to cancel if it keeps raining like it is.