Mesoscale Precipitation Discussion 0821
NWS Weather Prediction Center College Park MD
1117 PM EDT Mon Sep 10 2018

Areas affected...Deep South Texas and Texas Coastline....

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

Valid 110320Z - 110900Z

SUMMARY...Slow moving, highly efficient convection near the coast
and stalled mid-level wave in Deep South Texas.

DISCUSSION...At the tail end of the large scale westerly trof, an
inverted low level trof and possible closed 850mb wave remains
across far Deep South Texas into Northeast Old Mexico.  Current
GOES-16 satellite suite suggests the MCV/wave is just south of the
Rio Grande near Rio Grande City, TX with maximized low level
moisture convergence to spark cycling moderate sized updrafts with
tops cooling occasionally to -70C.  WV suite, denotes the western
edge of the Subtropical jet from Central Nuevo Leon to across
Starr and paralleling the TX coast before angling north to an
exiting mid-level shortwave near Austin to College Station, TX.  
Moisture remains pooled across Deep South TX, with total PWATs
near 2.5".  With freezing levels aoa 15Kft, warm cloud processes
similar to the past few days remain with scattered convection that
develops. Given weak inflow, cells have been maintained about 1-2
hours and with mean cell motions less than 10kts...localized
totals over 2-3" remain likely resulting in potential flash
flooding.

Later in the period, toward 05/06z, low level surface flow will
slightly increase with general confluence along the coast enhanced
by frictional convergence particularly near points/bays/coves that
will spark new development.  Upper level winds are weak, but
generally unidirectional to support slightly tilted updrafts
(downdrafts) for slightly downstream rainfall that should not
choke inflow...leading to persisent heavy rainfall and potential
flash flooding along the coast line from Kenedy county to
Galveston Bay.  HREF mean suggests greatest threat remains near
Baffin to Aransas Bay, though a few showers development can be
seen as far NW as Matagorda Bay.  Increase of 850mb flow toward
07z up to 15kts from the due south has the potential to reduce
coastal flash flooding, leading to propagation offshore after
07z...though shifts threat for best coastal convergence toward
Galveston.  Given repeat nature over past few days, soils have
become more saturated and susceptible to hydrophobic conditions
leading to greater flooding/inundation to occur.  As such flash
flooding/inundation is considered possible through 09z. 

Gallina

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

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

LAT...LON   29909491 29889462 29739446 29389442 29289458
            28799539 28359615 27899684 27079725 26379710
            25999703 25779726 25809762 26089842 26279898
            26439925 26819941 27199920 27779811 29129662
            29569586 29779533