Flash Flood in Texas, August 12, 2003

DEEP SOUTH TEXAS FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
150 PM CDT TUE AUG 12 2003

.DISCUSSION...THE FIRST HINTS OF PROBABLE CONVECTION OVR THE RGV
BEGAN JUST AFTER NOON TDY...AS SEA BREEZE FIRST TO INITIATE
CONVECTION. THIS WILL ALL CHANGE...AS TIME PROGRESSES...WITH UPPER
LEVEL ENERGY AND LOW AND MID LVL MSTR ADVECTION TAKING OVER. LATEST
GUIDANCE FROM 12Z AVN PUSHES RARE 100 PERCENT POPS FOR ALL VALLEY
LOCATIONS NOW THRU 12Z WED. TROF AXIS MVS FM EAST TO WEST...PLACING
RGV IN DEEP SOUTH FLOW BY LATE THIS PM...WITH SATURATED ATM AND
VIGOROUS UVM. THIS SATURATION OF OUR ATM AND AVAILABLE LIFT FM S/WV
ENERGY REMAINS IN PLACE THRU LATE THU...WITH UPPER HIGH RIDGING IN
FOR A SHORT DURATION FRI EARLY MRNG...THEN EASTERLY WAVE/GULF SFC
LOW PRESSURE EXERTS ITS INFLUENCE ON OUR REGION WITH ENERGY AND
MSTR ADVECTION AND RESULTING SHRAS/TSRAS LATE FRI NGT INTO SATURDAY.
MAX TEMPS WILL BE HAMPERED BY RAFL (WET-BULBING) AND OVC SKIES THRU
MOST OF THIS WEEK. WILL PLACE HIGHS IN UPPER 80S TO NEAR 90.

BOTH AVN AND ETA PLACE DEEPENING GULF SFC LOW APPROXIMATELY 300
MILES EAST OF POR BY 1 PM FRI...DEEPENING WITH TIME AS IT ROTATES
OVER VERY WARM GULF WATERS (SST 86 AND 87 DEG F OVR MOST OF THE
CENTRAL AND WESTERN GULF). BY 7 PM FRI...BOTH ETA AND AVN PLACE
DEEPENING SFC LOW 240 MILES SOUTHEAST OF POR...BRINGING COPIOUS RAFL
FM THE GULF INTO DEEP S TX LATE FRI AND HVY RAIN BLANKET OUR REGION
SAT WITH FLOODING POSSIBLE AFTER OUR RETRO LOW DUMPS 2 TO 4 INCHES
NOW THRU FRI. STRONG S/WV ENERGY MVS N TO S THRU THE BASE OF THE
TROF...INITIATING STRONG VERTICAL MOTION AND DRAWING PWATS OF 2.35
INCH TO THE RIO GRANDE VALLEY OVERNGT. AVN MAINTAINS GOOD RUN TO RUN
CONSISTENCY...AND XPCT VIGOROUS CONVECTION TO DEVELOP NORTH OF OUR
REGION AND MV INTO DEEP S TX OVRNGT. AMS OVR DEEP SOUTH TEXAS FLOW
IN THE VERTICAL GOES FROM OUR CURRENT NORTH FLOW TO SOUTH OVR DEEP
SOUTH TEXAS AS TROF AXIS RETROS WEST OF THE REGION. DEEP NORTH FLOW
REMAINS OVR BRO AT 1830Z...WITH DISPLACEMENT OF AXIS WEST IMMANENT
BUT TIMING UNSURE ATTM.

WILL BUMP POPS A CAT TO LIKELY AND MAY NEED FLASH FLOOD WATCH
POSTING SOON...WHEN CONVECTION SHOWS ITSELF. ATTM...WILL MAINTAIN
LIKELY POPS THRU 1ST THREE PDS....HIER WEST...FOR THIS PM AND
EVENING...AS NO CONVECTION HAS SHOWN ITSELF NORTH ATTM. AN INCREASE
IN POPS AGAIN MAY BE NEEDED ON AN UPDATE...IF CONVECTION BEGINS
DURING MID PM.

MARINE...AT 8 AM BUOY020 REPORTED SOUTH WINDS AT 6 KNOTS WITH SEAS 2
FOOT. AT NOON...BUOY REPORTED WINDS NORTH AT 10 KNOTS WITH 2 FOOTERS
AT 5 SEC PD. OBVIOUSLY...WX PATTERNS CHANGING QUICKLY. UPPER LEVEL
LOW PRESSURE WILL CONTINUE TO ENHANCE SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS THE COASTAL WATERS THROUGH THE NEXT SEVERAL
DAYS. LIGHT TO MODERATE ONSHORE FLOW WILL PREVAIL DURING THIS TIME.
ONSHORE WINDS WILL BEGIN TO INCREASE THURSDAY IN RESPONSE TO A
TROPICAL WAVE MOVING WESTWARD ACROSS FLORIDA INTO THE EASTERN GULF.
THIS WAVE WILL BRING ANOTHER SIGNIFICANT AMOUNT OF PRECIPITATION TO
THE WATERS FRIDAY THROUGH THE WEEKEND.

AVIATION...MAIN AVIATION CONCERNS REVOLVE AROUND EXPECTED SHOWERS
AND THUNDERSTORMS. VFR CONDITIONS WILL PREVAIL BUT AVIATION
CONDITIONS WILL DETERIORATE NEAR THUNDERSTORMS WITH VIS LESS THAN 3
MILES AND STRONG AND VARIABLE GUSTY WINDS. CIGS CUD DROP TO OVC010CB
IN TSTMS.

.PRELIMINARY POINT TEMPS/POPS...
BROWNSVILLE         BC 075/088 075/088 075 30/50/60/60/60
HARLINGEN           BC 074/089 074/089 074 30/50/60/60/60
MCALLEN             BC 075/090 075/090 075 30/50/60/60/60
RIO GRANDE CITY     BC 074 090 074/090 074 30/50/60/60/60
SOUTH PADRE ISLAND  BC 079/087 078/087 078 30/50/60/60/60

.BRO WATCHES/WARNINGS/ADVISORIES...NONE.

58/64

THIS PRODUCT IS ALSO AVAILABLE ON OUR INTERNET WEB PAGE AT:
HTTP://WWW.SRH.NOAA.GOV/BRO

TXZ248>257-131100-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BROWNSVILLE TX
235 PM CDT TUE AUG 12 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR DEEP SOUTH TEXAS.

.DAY ONE...TODAY AND TONIGHT.

A MOIST AND UNSTABLE ATMOSPHERE...IN COMBINATION WITH A LINGERING
SEA BREEZE FRONT AND DAYTIME HEATING...WILL GENERATE SCATTERED
SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND THIS EVENING. SOME OF
THESE STORMS MAY BE BE SEVERE...PRODUCING WIND GUSTS IN EXCESS OF 60
MPH...HEAVY RAIN...FLOODING OF ROADWAYS...FREQUENT LIGHTNING AND
HAIL.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH SUNDAY.

AN UPPER LEVEL TROUGH WILL APPROACH FROM THE NORTHEAST ON TUESDAY
THEN MOVE WESTWARD INTO MEXICO BY THURSDAY. THIS SYSTEM WILL
DESTABILIZE THE ATMOSPHERE AND INCREASE THE CHANCES FOR SHOWERS AND
THUNDERSTORMS. SOME OF THE SHOWERS AND THUNDERSTORMS COULD PRODUCE
STRONG GUSTY WINDS AND HEAVY RAINS. SCATTERED SHOWERS AND
THUNDERSTORMS WILL TAPER TO ISOLATED COVERAGE FRIDAY AS THE UPPER
LEVEL TROUGH MOVES FARTHER WEST INTO NORTHWESTERN MEXICO AND UPPER
LEVEL HIGH PRESSURE BUILDS IN FROM THE WESTERN GULF.

.SPOTTER INFORMATION STATEMENT.

SPOTTERS AND EMERGENCY MANAGERS ARE ASKED TO MONITOR WEATHER
CONDITIONS CLOSELY THIS AFTERNOON AND TONIGHT.