AWUS01 KWNH 040628
FFGMPD
TXZ000-041230-

Mesoscale Precipitation Discussion 0972
NWS Weather Prediction Center College Park MD
227 AM EDT Wed Sep 04 2024

Areas affected...South Texas...

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

Valid 040630Z - 041230Z

SUMMARY...Highly efficient rain producing, slow moving tropical
showers, particularly along the Lower Texas Coast.  Localized
2-3"/hr rates may result in localized totals over 5" resulting in
rapid inundation flooding.

DISCUSSION...Pesky pattern remains across the Northwest Gulf and
Deep South Texas again this morning; with core of mid-level
shortwave remaining along/just offshore of the Texas coast with
some peripheral interaction with base of the elongated northern
stream trough that exists across central TX into OK/AR attm.  VWP
and RAP analysis suggest 850-700mb low remains in the lower Rio
Grande Valley just southwest of Starr county in Mexico, which
continues to support solid easterly to northeasterly confluent
flow across the region advecting the anomalously high and deeply
saturated profile with 2.5"+ Total PWats.  The boundary layer
heating from the western Gulf continues to provide enough thermal
support for solid conditionally unstable air with MLCAPE values
over 2000-2500 J/kg across S Padre Island, reducing to 1000-1500
J/kg nearer the 850-700mb wave.

Recent RAP analysis suggests deep layer moisture convergence is
increasing along the 850-700 convergence axis from near LRD to
north of PIL.  This also is co-located with the col in deep layer
steering flow supportive of very slow cell motions for showers
that do develop.   Given all the factors, flux may be weak but
enhanced locally by isallobaric influences of developing
convection so rainfall efficiency will by tied to those flux
rates, but should be on the order to support 2-3"/hr; perhaps
instantaneously higher which could overwhelm any soil
condition/limiting infiltration resulting in rapid inundation
flooding.

Once again, hi-res CAMs are insistent on very high totals where
frictional convergence is maximized along the coasts/bays from
Corpus Christi southward.  00z HREF values of 3"/6hrs by 12z are
even higher than prior days at over 90% while 5" probability is
over 50% along much of the coastal length, with 30-50% of 3"/6hrs
and 15-25% of 5" as far west as Zapata/Jim Hogg county. While this
would normally aspire confidence, these magnitudes have been noted
over the last few days and mainly manifested off-shore as
propagation vectors were stronger than forecast as
inflow/convergence was offshore.  Howver, this evening's
placement/orientation of the 850-700mb low is observationally
further west, perhaps aiding greater convergence onshore and
therefore enhancing the potential for flooding conditions.  Recent
RADAR and 10.3um EIR trends would support this increased coverage
and potential.  As such, scattered spots of 3-5" and rapid
inundation flooding is considered possible, with greater coverage
more likely from Corpus Christi Bay southward toward E Cameron
county.

Gallina

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!7X-PHkczcUSlFQtBF55ols7XHwHVutIvbSquyDQF4j7FJSKCHvzvPJErFmokEqTYSJ1x=
_RpUA4nl8Ue7KTRgtZreWb8$  for graphic product...

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

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

LAT...LON   28449771 28389667 27769701 27079728 26159710=20
            25789732 25989821 26359913 26859946 27369963=20
            27649965 27909942 28209892 28359831=20

=3D =3D =3D
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