From Mike Powell@454:1/105 to All on Tuesday, October 03, 2023 08:31:00
AWUS01 KWNH 031007
FFGMPD
TXZ000-031606-
Mesoscale Precipitation Discussion 1127
NWS Weather Prediction Center College Park MD
606 AM EDT Tue Oct 03 2023
Areas affected...Southeast TX
Concerning...Heavy rainfall...Flash flooding possible
Valid 031006Z - 031606Z
SUMMARY...Increasing coverage of showers and thunderstorms may
pose at least an isolated flash flood risk as we head through the
morning hours across portions of coastal Texas.
DISCUSSION...Recent radar and satellite observations show
increasing convective coverage near and offshore the TX coast.
Robust instability and moisture is present offshore, with MLCAPE
in excess of 2000 J/kg and PWs over 2.25"...and over the next
several hours this airmass is expected to move inland. In fact
already seeing notable CAPE and PW increases onshore over the last
couple hours. Strong coastal convergence should help focus
additional convective development through the morning hours.
Currently most of this activity is rather shallow in nature, and
thus moving with the low level mean southeasterly flow. Above
~500mb flow turns more westerly, and thus deeper convective cells
will be in an environment with easterly low level flow and
westerly upper flow...which could be support some stationary
cells. Upwind propagation vectors are also from northwest to
southeast, which is opposite the low/mid level steering flow. Thus
wind profiles do support some backbuilding/training potential with
any cells that are able to grow deeper in nature.
Model guidance does support the potential of one or more narrow
linear training convective bands through the morning hours.
Initially cells onshore may struggle to gain depth and thus should
tend to move more steadily and be weaker in nature. However as
instability and moisture continues to increase through the morning
hours, we should be able to get some stronger/deeper convection
take hold onshore...which would then have the potential to locally backbuild/train over the same area. Given the high PWs and deep
warm layer in place, rainfall efficiency should be high,
supporting the potential for 2-3"/hr rainfall. The expectation is
that at least a localized flash flood risk will gradually evolve
this morning near the TX coast from approximately Point Comfort to
Houston.