Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 120539 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1239 AM CDT FRI SEP 12 2014

.DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

&&

.AVIATION...CONVECTION WILL BE INCREASING OVER THE NEXT 24 HOURS.
CURRENTLY SHOWERS ARE NOTED OVER THE COASTAL WATERS MOVING EAST
TOWARDS THE COAST. SCATTERED CONVECTION THIS MORNING BECOMES
NUMEROUS TO WIDESPREAD LATER THIS AFTERNOON AND TONIGHT. VFR
CONDITIONS EARLY ON TO BECOME MVFR AS THE SHOWER AND THUNDERSTORMS
INCREASE IN COVERAGE. CONFIDENCE IS HIGH ON POOR FLYING CONDITIONS
WITH ATMOSPHERE CONDITIONS BECOMING VERY CONDUCIVE FOR SHOWERS AND
THUNDERSTORMS WITH VERY DEEP MOISTURE PRODUCING A THICK CLOUD
COVER. LIGHT SOUTHEAST TO EAST WINDS WITH SOME OCCASIONAL STRONGER
GUSTS IN AND NEAR THE CONVECTION.

&&

.PREV DISCUSSION... /ISSUED 646 PM CDT THU SEP 11 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...LIGHT EAST TO SOUTHEAST WINDS WILL PREVAIL THROUGH
THE NIGHT WITH SHOWERS BEGINNING TO DEVELOP AFTER MIDNIGHT AS
A TROPICAL WAVE OVER THE GULF WATERS MOVES CLOSER TO THE AREA.
TEMPO GROUPS HAVE BEEN INCLUDED ON ALL TERMINALS ESPECIALLY FOR
THE EARLY MORNING HOURS BEFORE SUNRISE. THIS ACTIVITY COULD REDUCE
VISIBILITY AT TIMES WITH HEAVY DOWNPOURS AND COULD PRODUCE
LIGHTNING AFTER SUNRISE AND BECOME MORE WIDESPREAD THROUGH THE
MORNING HOURS FRIDAY. A BREAK IS POSSIBLE CLOSER TO NOON BUT
EXPECT ANOTHER ROUND OF SHOWERS TO INCREASE IN THE AFTERNOON.

PREV DISCUSSION... /ISSUED 257 PM CDT THU SEP 11 2014/

SHORT TERM /NOW THROUGH FRIDAY NIGHT/...UPPER LEVEL LOW CENTERED
ABOUT 150 MILES SOUTHEAST OF BROWNSVILLE IS MOVING WESTWARD FAIRLY
QUICKLY TODAY AND A STRONG TROPICAL WAVE IS TRACKING BEHIND IT
ABOUT TO EMERGE OFF THE WESTERN YUCATAN PENINSULA. UPPER LEVEL
TROUGHING OVER WYOMING/MONTANA IS MOVING EASTWARD OFF THE FRONT
RANGE ABOUT ON SCHEDULE...CONVERGENCE BEHIND THIS FEATURE WILL
STRENGTHEN PLAINS HIGH PRESSURE THAT WILL SEND A COLD FRONT...
CURRENTLY STALLED NORTH OF SAN ANTONIO...THIS DIRECTION BY
SATURDAY WHICH WILL FURTHER ENHANCE RAINFALL CHANCES.

TONIGHT...GOES SOUNDER AND AMSU/SSMI PRECIPITABLE WATER ESTIMATES
AND THE BEHAVIOR OF THUNDERSTORMS/ARC CLOUDS ON VISIBLE SATELLITE
SHOW THE LINE BETWEEN MOSTLY DRY MID ATMOSPHERIC AIR AND PRETTY
MOIST AIR IS STILL ABOUT 100 TO 150 MILES EAST OF SOUTH PADRE
ISLAND. ON ITS CURRENT TRACK...WHICH LINES UP PRETTY WELL WITH
RUC/NAM/GFS GUIDANCE THAT INCREASED MOISTURE SHOULD ARRIVE AFTER
MIDNIGHT TONIGHT. WILL STILL BE A LITTLE LOW ON LOW LEVEL
CONVERGENCE BUT AT LEAST ISOLATED TO SCATTERED SHOWERS SHOULD
START TO SPRING UP...ESPECIALLY EAST OF 281 IN THE EARLY MORNING
HOURS.

FRIDAY...BY MID TO LATE MORNING A MUCH MORE SATURATED AIR MASS SHOULD
BE IN PLACE WITH A LARGE PERCENTAGE OF THE COLUMN PROJECTED TO HAVE
RH VALUES OVER 70 PERCENT. THIS SHOULD WORK WITH WEAK DIVERGENCE
ALOFT FROM THE RETREATING UPPER LOW AND THE WEAK CONVERGENCE AHEAD
OF THE ADVANCING TROPICAL WAVE TO GENERATE WIDESPREAD SHOWER AND
THUNDERSTORM ACTIVITY BY THE AFTERNOON. LIGHT PREVAILING NORTHEAST
WINDS SHOULD ALSO HELP A DECENT SEA BREEZE FRONT GET STARTED...
ESPECIALLY IF THERE IS A LITTLE MORE SUN EARLY IN THE MORNING.
LOCALLY HEAVY RAINFALL IS POSSIBLE WITH PRECIPITABLE WATER VALUES
MOVING INTO THE 2.0 TO 2.2 INCH RANGE. A BRIEF DROP OFF IN
COVERAGE IS POSSIBLE IN THE LATE AFTERNOON AND EVENING AS DAYTIME
HEATING WANES.

FRIDAY NIGHT...THE MAIN 850/700MB TROUGH ASSOCIATED WITH THE
TROPICAL WAVE ARRIVES LATE FRIDAY NIGHT. STRONG CONVERGENCE IN THIS
AREA...WITH 850MB WINDS INCREASING TO AROUND 35 KTS...WHICH LOOKS
APPROPRIATE CONSIDERING CURRENT SCATTEROMETER AND GOES DERIVED WIND
FIELD PLOTS...PUMPS IN EVEN RICHER AND DEEPER MOISTURE WHICH SHOULD
WORK WITH THE LOW CONVERGENCE TO PRODUCE WIDESPREAD SHOWERS AND
STORMS. SOME TROPICAL BANDING SHOULD ALSO BE POSSIBLE IN THIS REGIME
AND WITH PWAT VALUES FROM NUMEROUS 12Z GUIDANCE MEMBERS RANGING FROM
2.2 TO 2.5 INCHES A MORE SIGNIFICANT THREAT FOR HEAVY RAINFALL AND
FLOODING EXISTS. STILL TOO EARLY FOR A FLASH FLOOD WATCH BUT WITH 6
HOUR FLASH FLOOD GUIDANCE AROUND 3 INCHES ENOUGH OF A RISK MAY
DEVELOP TO REQUIRE A WATCH DURING LATER SHIFTS. MAIN THREAT WILL BE
IF ANY BANDING SETS UP OVER THE METROPOLITAN AREAS WHICH COULD
PRODUCE A QUICK 4 TO 5 INCHES OF RAINFALL. AREA AVERAGES WILL BE
LESS...LIKELY AROUND 1 TO 2 INCHES. /68-JGG/

LONG TERM /SATURDAY THROUGH WEDNESDAY/...MAIN FORECAST CHALLENGE
FOR THIS PD WILL BE RAIN ON SATURDAY. FOLLOWING UP FROM FRIDAY...
A DISSIPATING FRONT OVER THE RGV WILL INTERACT WITH TROPICAL WAVES
MOVING ACROSS THE SOUTHWEST GULF TO POTENTIALLY PRODUCE SEVERAL
INCHES OF RAIN FOR THE AREA. MANY LOCATIONS COULD ACHIEVE THEIR
MONTHLY RAINFALL AVERAGE FOR SEPTEMBER OF FOUR TO SIX INCHES. THE
HEAVIEST RAINFALL AMOUNTS ARE EXPECTED ON SAT AS THE INGREDIENTS
COME TOGETHER...CONCENTRATED MAINLY OVER THE LOWER VALLEY AND ALONG
THE RIVER HEADING INLAND TO THE MID AND UPPER VALLEY. AMOUNTS FOR
THE NORTHERN COUNTIES AND THE BRUSH COUNTRY/RANCH LANDS MAY BE A BIT
LESS. SEPTEMBER IS OUR WETTEST MONTH FOR THE SAME REASONS AS WILL BE
IN PLAY THIS WEEKEND. THE UPPER ATMOSPHERE STEERING FLOW THIS TIME
OF YEAR TENDS TO CHANNEL TROPICAL MOISTURE TOWARD THE LOWER TEXAS
COAST...AND WHEN STILL RELATIVELY WEAK AUTUMN FRONTS COME INTO THE
PICTURE...WITH THE POTENTIAL TRIGGERING LIFT...ENHANCED RAINFALL
SCENARIOS ARE THE RESULT.

SATURDAY...CONFIDENCE IS HIGH FOR RAIN...OCCASIONALLY HEAVY...OVER
MOST OF THE CWA. A HALF INCH TO AN INCH AND A HALF OF ACCUMULATION
SHOULD BE THE NORM FOR MOST OF THE VALLEY. DUE TO THE THICKER CLOUD
COVER...HIGH TEMPS WILL BE HELD DOWN INTO THE MIDDLE 80S. URBAN
FLOODING WILL BE LIKELY IN ANY POPULATED AREAS AND ESPECIALLY IN
AREAS WITH POOR DRAINAGE.

SATURDAY EVENING INTO SUNDAY...LIGHTER RESIDUAL RAINS WILL OCCUR...
BUT SOME SHOWERS OR THUNDERSTORMS COULD BECOME GULLY WASHERS WITH
HEAVY RAIN. A SEA BREEZE MAY BE A POSSIBILITY WITH LIGHT ONSHORE
WINDS AND THE REMAINING ELEVATED MOISTURE. HIGH TEMPS SUNDAY WILL
REMAIN DEPRESSED IN THE 80S.

CHANCES FOR RAIN WILL LINGER INTO MONDAY AND TUESDAY DUE TO THE OLD
FRONTAL BOUNDARY REMAINING IN THE AREA PROVIDING A FOCUS FOR LIFT.
NONETHELESS...HIGH TEMPS WILL BEGIN TO DRIFT UP AS MORE SUNSHINE
ENTERS THE PICTURE.

STILL A BIT EARLY FOR A FLASH FLOOD WATCH BUT CONFIDENCE IN HEAVIER
SOAKING RAINS IS HIGH. FLASH FLOODING WILL DEPEND ON STORM DURATION
AND TRAINING. WIDESPREAD MODERATE RAINFALL LAST WEEK HAS PRIMED SOIL
CONDITIONS SOMEWHAT AND FLASH FLOOD GUIDANCE IS 1 TO 2 INCHES LOWER
THEN BEFORE LAST WEEK`S RAINFALL...BUT IS STILL 3 TO 5 INCHES IN AN
HOUR. MAINTAINED POPS AT 80 PERCENT SATURDAY ACROSS THE ENTIRE RIO
GRANDE VALLEY REGION WHICH IS IN LINE WITH MODEL GUIDANCE.

SUNDAY THROUGH WEDNESDAY...MID LEVEL MOISTURE WILL BEGIN TO DRY OUT
AND THE MODELS ARE PRETTY CONSISTENT ON TAPERING OFF RAIN CHANCES...
THOUGH RESIDUAL MOISTURE WILL BE PRESENT AND COULD COUPLE WITH A
LIGHT EASTERLY WIND AND THE OLD FRONT STATIONARY JUST OFF THE LOWER
TEXAS COAST. 850-700MB WINDS REMAIN SOUTHEAST WHICH SHOULD AIDE IN
THE LOW TO MID LEVEL CONVERGENCE. 30-40 PERCENT POPS SHOULD SUFFICE
SUNDAY AND MONDAY AND 20-30 PERCENT TUESDAY AND WEDNESDAY AT THIS
TIME. SLOW RECOVERY OF TEMPERATURES EXPECTED WITH THE SLOW DRYING.

MARINE...
NOW THROUGH FRIDAY NIGHT...LIGHT TO MODERATE EAST TO SOUTHEAST
WINDS ARE FORECAST THROUGH THE REST OF THE DAY WITH LOW TO
MODERATE SEAS. MOISTURE STREAMING IN FROM THE EAST IS EXPECTED TO
SPARK AN INCREASE IN SHOWER AND THUNDERSTORM ACTIVITY OVER THE
LOWER TEXAS COASTAL WATERS STARTING TONIGHT AND ESPECIALLY ON
FRIDAY AND FRIDAY NIGHT. SOUTHEASTERLY WINDS ARE EXPECTED TO
INCREASE ON FRIDAY NIGHT AS A TROPICAL WAVE MOVES INTO THE AREA.
EXERCISE CAUTION CONDITIONS ARE EXPECTED WITH ADVISORY CONDITIONS
POSSIBLE DUE TO ROUGHENING SEAS. MARINERS ARE ASKED TO CHECK THE
LATEST FORECASTS BEFORE DEPARTING.

SATURDAY THROUGH MONDAY...BORDERLINE SMALL CRAFT ADVISORY CONDITIONS
WILL BE POSSIBLE SATURDAY AS LONG PERIOD SWELLS MOVE NORTHEAST ON
FRESH SOUTHEAST WINDS OVER THE SOUTHWEST GULF. NUMEROUS MARINE
SHOWER AND THUNDERSTORM ACTIVITY WILL BE ONGOING SATURDAY AS A
TROUGH OF LOW PRESSURE FORMS ALONG THE NORTHEAST MEXICAN COAST.
LOWERED VISIBILITY OF 3 TO 5 MILES AND STRONG GUSTY WINDS WILL BE AN
ISSUE FOR BOATERS IN AND NEAR CONVECTION. ROUGHER SURF COULD RUN UP
TO THE DUNE LINE...ESPECIALLY SATURDAY EVENING NEAR HIGH TIDE.
CROWDS RETURNING TO THE BEACH SUNDAY AFTER A WASHOUT ON SATURDAY
WILL FACE AN ELEVATED RIP CURRENT RISK.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  87  81  84  77 /  80  80  80  50
BROWNSVILLE          88  79  84  76 /  80  80  80  50
HARLINGEN            88  79  85  75 /  80  80  80  50
MCALLEN              89  79  85  75 /  80  80  80  50
RIO GRANDE CITY      91  78  84  74 /  80  80  80  50
SOUTH PADRE ISLAND   87  81  83  79 /  80  80  80  50

&&

.BRO WATCHES/WARNINGS/ADVISORIES...
TX...NONE.
GM...NONE.
&&

$$

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