189
AWUS01 KWNH 191851
FFGMPD
TXZ000-200050-

Mesoscale Precipitation Discussion 0468
NWS Weather Prediction Center College Park MD
250 PM EDT Wed Jun 19 2024

Areas affected...South Texas

Concerning...Heavy rainfall...Flash flooding likely

Valid 191850Z - 200050Z

SUMMARY...Bands of locally training showers and thunderstorms
associated with the outer circulation of Tropical Storm Alberto
will continue to cross through South Texas this afternoon and
evening. Areas of flash flooding will be likely.

DISCUSSION...The latest GOES-E IR satellite imagery in conjunction
with regional dual-pol radars and surface observations shows bands
of heavy showers and thunderstorms focusing across South Texas as
the cyclonic circulation around the northwest flank of T.S.
Alberto overspreads the region.

An easterly low-level jet of 40 to 50 kts off the Gulf of Mexico
continues to drive strong low-level moisture flux convergence and
forcing in vicinity of an inverted trough. This coupled with a
substantial pool of offshore instability with MLCAPE values of
1500 to 2500 J/kg should sustain these convective bands along and
inland of the coast over the next several hours, with potentially
some uptick in intensity given some threat for the low-level jet
to increase a bit further in strength.

The environment remains deeply tropical with extremely high PWs
that are near or at a daily record. The 12Z RAOBs from CRP and BRO
depicted PWs of 2.64 and 2.66 inches respectfully. The very deep
warm cloud layer environment coupled with the sustained
instability transport and level of forcing for some of these
linear convective bands will continue to favor extremely high
rainfall rates that should easily reach into the 2 to 3 inch/hour
range. The 12Z HREF guidance suggests some spotty hourly totals
could reach 4+ inches with the stronger and more organized bands.

The 12Z HREF consensus and recent HRRR runs support an additional
3 to 6 inches of rain locally across South Texas going through the
early evening hours. Much of South Texas had been quite dry ahead
of T.S. Alberto`s rainfall, but with the locally extreme rainfall
rate potential and the additional totals, there will likely be
expanding areas of flash flooding over the next several hours.

In fact, areas around Rockport, TX on the coast have already seen
5+ inches of rain for the event, and are seeing flash flooding
now. Thus, with the additional rainfall today, a few instances of
considerable to severe flash flooding cannot be ruled out.

Orrison

...Please see www.wpc.ncep.noaa.gov for graphic product...

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

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

LAT...LON   29389694 29109603 28639584 27999668 27139711
            26239704 25809711 25779792 26109866 26689934
            27459950 27889989 28809918 29319818