AWUS01 KWNH 191251
FFGMPD
TXZ000-191850-

Mesoscale Precipitation Discussion 0467
NWS Weather Prediction Center College Park MD
850 AM EDT Wed Jun 19 2024

Areas affected...South-Central to Southeast TX

Concerning...Heavy rainfall...Flash flooding possible

Valid 191250Z - 191850Z

SUMMARY...The broken outer rainbands associated with Potential
Tropical Cyclone One will be arriving this morning across
south-central to southeast TX. Heavy rainfall rates and eventually
some concerns for training convection will support a gradually
increasing threat for flash flooding.

DISCUSSION...Potential Tropical Cyclone One remains situated down
over the southern Gulf of Mexico early this morning, but the
broken outer rainbands around the northwest flank of the system's
circulation are approaching the middle and lower TX coastlines and
will begin to move inland over the next several hours.

Cloud top temperatures in the GOES-E IR satellite imagery have
been tending to cool a bit overall over the last couple of hours
with the offshore activity, and this is largely be driven by
increasing low-level moisture flux convergence and instability
transport focusing along inverted surface trough. MLCAPE values
offshore over the western Gulf of Mexico are on the order of 1500
to 2500 J/kg, and with notable low-level speed convergence and
even frictional convergence near the coast, there will likely be
an increased level of convection becoming concentrated very close
to the coast and also just inland over the next several hours.

The environment is extremely moist around the northwest quadrant
of the system circulation, with PWs that are on the order of 2.4
to 2.6 inches based on early-morning GPS-derived data and the
latest CIRA-ALPW data shows highly concentrated moisture all the
way through the top of the vertical column. The very deep warm
cloud layer environment coupled with the instability transport and strengthening vertical ascent along the coast will support these
bands of convection producing extremely high rainfall rates that
should easily reach into the 2 to 3 inch/hour range, and may
approach 4 inches/hour for some of the stronger convective cells
by midday that will likely arrive once stronger instability begins
to overspread the coast.

Dry antecedent conditions will initially cut down on the flash
flooding risk, but over time, the arrival of heavier rainfall
rates and eventually cell-training concerns, should elevate the
flash flood threat. As depicted by the 06Z HREF consensus,
rainfall amounts going through early afternoon may reach 3 to 6
inches, and this will at a minimum support an urban flash flood
threat. Trends will be closely monitored over the next several
hours, and additional MPDs will be issued this afternoon
accordingly.

Orrison

ATTN...WFO...BRO...CRP...EWX...HGX...

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

LAT...LON 29459553 28979521 28499599 27799680 26799716
25779721 25699802 25969846 26839867 27859840
28639783 29289677
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