AWUS01 KWNH 050907
FFGMPD
TXZ000-051500-

Mesoscale Precipitation Discussion 1089
NWS Weather Prediction Center College Park MD
507 AM EDT Sat Oct 05 2024

Areas affected...Deep South Texas...

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

Valid 050910Z - 051500Z

SUMMARY...Persistent highly saturated, unstable onshore flow may
support periods of scattered efficient showers/thunderstorms
capable of 2-2.5"/hr rates and localized 3"+ totals. Given
recently wetted grounds, additional intense rainfall may result in
possible flash flooding this morning.

DISCUSSION...Large scale cyclonic gyre centered in southern Gulf
of Mexico/Western Bay of Campeche has seen a persistent convective
flare up throughout the evening. The broader easterly to
northeasterly flow has been persistent through the overnight
period and brought some transistory but intense tropical
showers/thunderstorms across Deep South Texas. The solid 15-20kts
of onshore surface to boundary layer flow has been transporting
.95-1.1" precipitable water in that layer per CIRA LPW. RAP
analysis shows small surface heating over 80F over high 70s Tds
and fairly saturated deep moisture profile to support unstable air
with SBCAPEs of 1500-2500 J/kg to support stronger updraft
strength and further vertical moisture flux to support efficient
rainfall production. Rates of 2-2.5"/hr will remain probable
throughout the morning, much as as they have for the last 6 hours
or so. Spots of up to 1.5-3" have been observed between Bayview
and Harlingen matching RADAR estimates, so values higher to the
northeast over Laguna Madre and S Kenedy county nearing 4-5" seem
plausible.

The area has been fairly dry and FFG values suggest that this
rainfall was able to be infiltrated fairly well, but now upper
soil profiles from this 1-3" total will have reduced FFG values
which are in the 2-3"/hr, 2.5-4"/3hr should be lowered. Over the
next six hours, the environment will remain very similar and
GOES-E 3.9um SWIR shows upstream shallow convective roll-clouds
moving through the northeasterly flow in the NE Gulf that start to
grow vertically near the coast given enhanced frictional speed
convergence. As such, similar transient thunderstorms with
2-2.5"/hr rates capable of 3-5" localized totals may continue
through the later morning hours, especially as low level flow may
increase under influence of the stregthening convective
cluster/surface reflection east of Tampico, MX. Winds may back a
bit more out of the NE, enhancing convective potential across E
Willacy and Cameron counties. HREF probability of exceeding 3" by
15z are 40-60% with 5" values near 25%. So with each passing
convective cell, the potential for localized flash flooding
increases slightly as longer term totals reach/exceed 5",
especially near urban locales.

Gallina

ATTN...WFO...BRO...

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

LAT...LON 26789776 26749731 26409718 25979710 25819736
25989777 26059827 26259843 26619820
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