MESOSCALE PRECIPITATION DISCUSSION 0621
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
448 AM EDT TUE AUG 30 2016
 
AREAS AFFECTED...PORTIONS OF SOUTHERN TX AND THE MIDDLE/LOWER TX
COAST 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 300845Z - 301445Z
 
SUMMARY...VERY HEAVY RAINFALL FROM TRAINING BANDS OF SHOWERS AND
THUNDERSTORMS IS EXPECTED THROUGH MID-MORNING. FLASH FLOODING IS
POSSIBLE.

DISCUSSION...BANDS OF HEAVY SHOWER AND THUNDERSTORM ACTIVITY HAVE
BEEN DEVELOPING AND BECOMING BETTER ORGANIZED OVER THE LAST COUPLE
OF HOURS ALONG THE MIDDLE TX COAST FROM NEAR CORPUS CHRISTI
NORTHEAST UP TO NEAR PALACIOS..AND EXTENDING OFFSHORE ACROSS THE
FAR WESTERN GULF OF MEXICO. THIS IS NOTED WITH THE RAPID COOLING
OF CONVECTIVE CLOUD TOPS OVER THE REGION...AND THE LATEST GOES-OTD
ALGORITHM DOES SHOW A FEW OVERSHOOTING TOPS NEAR AND JUST
OFFSHORE. THE ACTIVITY IS IN ASSOCIATION WITH A WEAK MID LEVEL
TROUGH DRIFTING SLOWLY SOUTHWESTWARD NEAR THE TX COAST ALONG WITH
A WELL-DEFINED SURFACE TROUGH AND EVIDENCE OF A SURFACE LOW THAT
IS HELPING TO CONCENTRATE DEEP TROPICAL MOISTURE AND INSTABILITY
INTO THIS BOUNDARY.

GPS-DERIVED PWATS ARE VERY HIGH GIVEN THE INFLUX OF DEEP TROPICAL
MOISTURE IN OFF THE GULF OF MEXICO...WITH VALUES RANGING AS HIGH
AS 2.2 TO 2.4 INCHES. MEANWHILE...A MODERATELY UNSTABLE AIRMASS IS
POOLED NEAR THE TX COAST IN VICINITY OF THE TROUGH WITH A SHARP
GRADIENT NOTED IN THE LATEST RAP ANALYSIS.

THE LATEST HIRES GUIDANCE SHOWS A CONTINUATION OF LOW LEVEL
EASTERLY FLOW THIS MORNING INTO THE TROUGH AXIS...WITH  RATHER
STRONG VALUES OF MOISTURE FLUX CONVERGENCE FOCUSING ALONG IT. THIS
WILL ALLOW FOR CONCENTRATED BANDS OF VERY HEAVY SHOWERS AND
THUNDERSTORMS TO CONTINUE TO DEVELOP JUST OFFSHORE AND MOVE JUST
INLAND.

RAINFALL RATES WILL BE CAPABLE OF EXCEEDING 3 INCHES/HR WITHIN
THESE CONVECTIVE BANDS...AND THE HIRES GUIDANCE SHOWS RAINFALL
TOTALS AS HIGH AS 5 TO 7 INCHES LOCALLY THROUGH MID-MORNING. FLASH
FLOODING WILL BE POSSIBLE AS A RESULT.

ORRISON

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

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

LAT...LON   29139592 28779560 28179655 27419705 26749712 
            26499765 26869805 27589802 28389757 28929675 
            
A