MESOSCALE PRECIPITATION DISCUSSION 0224
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
819 AM EDT TUE JUN 16 2015
 
AREAS AFFECTED...SOUTHEAST TEXAS 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 161217Z - 161817Z
 
SUMMARY...NARROWLY FOCUSED CORES OF VERY HIGH RAINFALL ON EASTERN
SIDE OF T.S. BILL TO LIKELY PRODUCE FLASH FLOODING.

DISCUSSION...AS THE CENTER OF TROPICAL STORM BILL NEARS THE COAST
CONVECTIVE TRENDS SUPPORTED BY HI-RESOLUTION MODEL GUIDANCE
STRONGLY SUGGESTS A SMALL BUT VERY HIGH IMPACT AREA OF SIGNIFICANT
PROLONGED HEAVY RAINFALL NEAR MATAGORDA BAY BY 18Z.  THE EASTERN
INNER BAND/CORE HAS BEEN INCREASING IN INTENSITY OVER THE LAST FEW
HOURS IN RESPONSE TO INCREASED CONVERGENCE ALONG THE SOUTHEAST
QUADRANT OF THE INNER CORE.  THIS APPEARS TO BE IN RESPONSE TO
LOBE OF THE MIDDLE VORTICITY ROTATING ALONG THE SOUTHERN AND
SOUTHEASTERN SIDE IN THE LAST FEW HOURS.  THIS HAS ALLOWED FOR
INCREASED DEPTH AND HENCE EFFICIENCY OF RAIN RATES IN EXCESS OF
2-3"/HR IN THIS CORE...GIVEN THE VERY DEEP MOIST PROFILE WITH
TOTAL PWATS AOA 2.5".   TRENDS IN HI-RES GUIDANCE...ESPECIALLY THE
ARW AND NMMB APPEAR TO KEEP THIS MAXIMIZED CORE ALONG THE
SOUTHEAST QUADRANT OF THE SURFACE CENTER AND EVEN THOUGH THEY
APPEAR A BIT SLOW WITH THE TIMING AND  RECENT JOGGING SLIGHTLY
WEST OF THE CENTER... THE HEAVIEST CORE SHOULD REMAIN JUST
OFFSHORE OR NEAR MATAGORDA BAY THROUGH 13-14Z AS MAXIMIZED
CONVERGENCE WILL CONTINUE TO BE ON THE SOUTH SIDE HOWEVER STRONG
LOW TO MID-LEVEL CONFLUENT SOUTH EASTERLIES ON THE EASTERN
SIDE...A BROADER AREA OF MODERATE SHIELD PRECIPITATION IS TO BLOW
DOWNSTREAM PRODUCING RATES AROUND .5-1"/HR.  THIS SHOULD SET THE
STAGE FOR TOTALS NEAR 2-4" IN THE NEXT 6HRS ACROSS MATAGORDA,
WESTERN BRAZORIA...ESPECIALLY WITH INCREASED FRICTIONAL
CONVERGENCE FOR POTENTIAL ENHANCED VERTICAL GROWTH AND CELL
EFFICIENCY. THE TIMING OF THE EXTREME RATES ON THE SOUTH/SOUTHEAST
HEMISPHERE SHOULD BEGIN TO AFFECT THE MATAGORDA BAY REGION TOWARD
16-18Z AS THE CENTER MOVES ASHORE... NESDIS E-TRAP 6HR TOTALS
ENDING AT 18Z SUPPORT THIS IDEA WITH 5" MAXIMA ABOUT 30 MILES
SOUTHEAST OF PSX.

FURTHER NORTHEAST...HOUSTON VICINITY...
OUTER BAND IS WELL ORIENTED PERPENDICULAR TO THE COAST FOR THE
POTENTIAL FOR TRAINING CONVECTION OF THE BAND.  HOWEVER...RADAR
LOOP SHOWS SOME ARCING OF THE CONVECTIVE ELEMENTS SUGGESTING AN
AREA OF SLIGHTLY INCREASED MID-LEVEL DRYING...ALLOWING FOR THEM TO
BE OUTFLOW DOMINANT AND DISRUPTING THE POTENTIAL FOR EXTREME
TRAINING.  THIS SHOULD REDUCE THE POTENTIAL FOR HIGHER TOTALS IN
THE NEAR TERM.  

GALLINA

ATTN...WFO...CRP...EWX...HGX...LCH...

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

LAT...LON   30179457 29619407 29099518 28269655 28119684 
            28259719 28659739 29309690 29629647