Area Forecast Discussion
Issued by NWS Brownsville, TX

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FXUS64 KBRO 271647 AAB
AFDBRO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1147 AM CDT WED AUG 27 2014

.DISCUSSION...LATEST FORECAST TRENDS SUGGEST A DECREASE IN AREAL COVERAGE
OF THUNDERSTORMS AND A DELAY ON THE ONSET OF SHOWERS AND THUNDERSTORMS
IN THE RIO GRANDE VALLEY. WEAK SEA BREEZE AND A SUBTLE INCREASE IN
MOISTURE ARE COMBINING WITH THE DAYTIME HEATING TO PRODUCE
ISOLATED SHOWERS ALONG THE IMMEDIATE COAST LATE THIS MORNING. THE
BROAD CYCLONIC CIRCULATION AROUND THE SURFACE LOW, CENTERED
APPROXIMATELY 165 MILES ENE OF PORT ISABEL, IS PRODUCING A
NORTHERLY WIND OR PARALLEL FLOW ALONG THE COAST. THIS SHOULD LIMIT
THE WESTWARD MOVEMENT OF THE SEA BREEZE FRONT. THUS, HAVE LOWERED
POPS ACROSS THE MIDDLE AND UPPER VALLEYS FOR THE AFTERNOON. KEPT
THE 30 PERCENT POPS FOR THE COASTAL COUNTIES THIS AFTERNOON BUT
CONFIDENCE IS LOW IF COVERAGE WILL MEET THESE NUMBERS WITH THE
REGION STILL ON THE WEST OR SUBSIDENCE SIDE OF THE LOW PRESSURE
AREA. BETTER CHANCES FOR MOST AREAS TO SEE RAIN, SOME HEAVY...IS
STILL ANTICIPATED THURSDAY AS THE LOW PRESSURE AREA APPROACHES THE
LOWER TEXAS COAST. ALL OTHER ELEMENTS REMAIN THE SAME.

&&

.DISCUSSION...UPDATED FOR LATEST MARINE DISCUSSION BELOW.

&&

.MARINE...A BIT MORE SUSTAINED HIGHER WINDS DUE TO THE SLIGHTLY
TIGHTER CIRCULATION AROUND THE LOW PRESSURE AREA APPROXIMATELY 165
MILES ENE OF PORT ISABEL HAVE ALLOWED FOR SEAS TO INCREASE THIS
MORNING. THE HIGHER WINDS AND SEAS TO PERSIST UNTIL THE LOW MOVES
INLAND LATER THURSDAY NIGHT. WINDS AND SEAS COULD APPROACH SMALL
CRAFT ADVISORY CONDITIONS FAR OFFSHORE WITH EXERCISE CAUTION
CLOSER TO SHORE ON THURSDAY.

&&

.PREV DISCUSSION... /ISSUED 623 AM CDT WED AUG 27 2014/

DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.

AVIATION...CLOUD COVER APPEARS TO BE HOLDING OFF THIS MORNING
DESPITE A LARGE INCREASE IN LOW LEVEL MOISTURE SO REMOVED THE
TEMPO GROUPS. EXPECTING SCATTERED SHOWERS TO BUILD INTO
THUNDERSTORMS THIS AFTERNOON AND ADDED TEMPO THUNDER GROUPS TO ALL
3 TAF SITES. PREVAILING CONDITIONS WILL BE VFR WITH BRIEF MVFR
VISBY POSSIBLE IN SHOWERS. SHIFTED A LITTLE MORE OPTIMISTIC ON CIG
TONIGHT TO VFR UNTIL 09Z BUT CONFIDENCE IS LOW ON TIMING THROUGH
THE OVERNIGHT. /68-JGG/

PREV DISCUSSION... /ISSUED 303 AM CDT WED AUG 27 2014/

SHORT TERM /NOW THROUGH THURSDAY/...

THE SETUP...THIS MORNING THERE IS WEAK UPPER LEVEL TROUGHING
SITUATED OVER THE COASTAL PLAINS OF TEXAS AND SLIGHTLY STRONGER
UPPER LEVEL RIDGING CENTERED ABOUT 100 MILES EAST SOUTHEAST OF
BROWNSVILLE. THE TROUGHING IS WEAKENING AS A LARGER POLAR
JET/TROUGH STRENGTHENS OVER THE WEST AND THE RIDGING IS SLOWLY
MOVING WESTWARD BRINGING WITH IT MUCH DEEPER AND RICHER MOISTURE
VALUES WHICH HAVE BEGUN MOVING INTO THE AREA PER AMSU/SSMI TOTAL
PRECIPITABLE WATER ESTIMATES. IR/ASCAT AND SURFACE OBSERVATIONS
SHOW A WEAK CONVECTIVELY INDUCED SURFACE CIRCULATION...LARGELY
DEVOID OF ANY CONVECTION AT THE MOMENT...ABOUT 170 MILES EAST
NORTHEAST OF BROWNSVILLE...ALSO DRIFTING WESTWARD AT ABOUT THE
SAME RATE AS THE UPPER RIDGE. THIS FEATURE IS MENTIONED IN THE NHC
TROPICAL WEATHER OUTLOOK AS AN EXTREMELY UNLIKELY CANDIDATE FOR
TROPICAL CYCLONE FORMATION. WATER VAPOR AND GOES SATELLITE DERIVED
WINDS CONTINUE TO CONFIRM 25 TO 30 KNOT UPPER LEVEL WINDS ABOVE
THE SURFACE CIRCULATION KEEPING ANY REAL ORGANIZATION/GROWTH
UNLIKELY. ALTHOUGH THE CIRCULATION DOES MAINTAIN SOME IDENTITY IN
GLOBAL MODEL RUNS AS IT DRIFTS WESTWARD INTO DEEP SOUTH TEXAS
HELPING TO ENHANCED SHOWER AND STORM ACTIVITY OVER THE NEXT 24
HOURS OR SO WHICH SEEMS REASONABLE.

TODAY...
IMPACT...SCATTERED MAINLY PM STORMS WITH LOCAL HEAVY RAINFALL
THREAT. NUMEROUS STORMS OFFSHORE.

LIGHT TO MODERATE NORTHEASTERLY WINDS WILL MAINTAIN OR INCREASE
SLIGHTLY AS THE SURFACE LOW APPROACHES. EXPECTING ABOUT 8 TO 15
MPH OVER THE LAND AREAS AND AROUND 15 KNOTS OVER THE MARINE ZONES.
THIS SHOULD ALLOW A STRONG SEA BREEZE FRONT TO ESTABLISH AND EXPECT
DAYTIME HEATING TO WORK WITH THE SEA BREEZE TO PRODUCE SCATTERED
SHOWERS AND THUNDERSTORMS TODAY STARTING IN THE MID TO LATE
MORNING AND LASTING THROUGH EARLY AFTERNOON. NUMEROUS SHOWERS AND
STORMS ARE FORECAST OVER THE MARINE AREAS THROUGH MOST OF THE DAY
AND ARE ALREADY STARTING TO SPARK ON RADAR THIS MORNING. AS UPPER
RIDGING MOVES OVERHEAD STEERING FLOW SHOULD BECOME VERY WEAK AND
ANY STORMS THAT FORM WILL LIKELY BE FAIRLY SLOW MOVING AND THIS
WILL WORK WITH PRECIPITABLE WATER VALUES AROUND 2.00 INCHES TO
PRODUCE A THREAT OF LOCALLY HEAVY RAINFALL WITH ANY STORMS THAT
GET GOING. STILL PREFER THE GFS/ECMWF OVER THE NAM WITH THIS SETUP
GIVEN EACH MODELS TRADITIONAL SKILL WITH THESE TYPE SYSTEMS.

TONIGHT...
IMPACT...NUMEROUS STORMS OFFSHORE...FEWER STORMS INLAND.

GFS/ECMWF SHOW BROAD 850/SFC TROUGHING WITH A WEAK CENTRAL
CIRCULATION APPROACHING THE COAST PROVIDING LOW LEVEL CONVERGENCE
FOR ISOLATED TO SCATTERED SHOWERS TONIGHT OVER LAND AND SCATTERED TO
NUMEROUS SHOWERS OVER THE MARINE ZONES. WINDS SHOULD BECOME PRETTY
LIGHT TONIGHT OVER LAND ALTHOUGH 15 TO 20 KNOT WINDS OVER THE MARINE
ZONES APPEAR TO BE AN INCREASING POSSIBILITY.

THURSDAY...
IMPACT...SLIGHTLY BETTER STORM CHANCE LOCAL HEAVY RAINFALL THREAT.
PERSISTS. NUMEROUS STORMS OFFSHORE.

THE SURFACE LOW MOVES ONSHORE BUT BROAD LOWER LEVEL TROUGHING
PERSISTS OVER THE AREA AMID VERY RICH AND DEEP MOISTURE AND EXPECT
DAYTIME HEATING AND ANOTHER GOOD SEA BREEZE FRONT TO AID IN
DEVELOPING AND ENHANCING SCATTERED SHOWERS AND STORMS THROUGH MID
TO LATE MORNING. A SIMILAR LARGE SCALE SETUP EXISTS BOTH WEDNESDAY
AND THURSDAY AND THE THREAT OF LOCALLY HEAVY RAINFALL WILL LIKELY
CONTINUE. GFS/ECMWF AGREE ON A SLIGHTLY HIGHER 850-700MB RH AND
BETTER LOW CONVERGENCE AND HAVE SLIGHTLY HIGHER PRECIP CHANCES IN
THE FORECAST THURSDAY AFTERNOON AS A RESULT. THE SPORADIC AND
DISORGANIZED NATURE OF THE EXPECTED CONVECTION BEING THE ONLY
LIMITING FACTOR ON PRECIP CHANCES AT THE MOMENT. /68-JGG/

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...MID LEVEL DUMBELL TYPE
HEIGHT CENTERS OVER FLORIDA AND SOUTHERN CALIFORNIA/BAJA WILL PART
IN THE MIDDLE LIKE THE BIBLICAL RED SEA AS AN EASTERLY WAVE MOVES
ALONG THE NORTHERN GULF COAST AND THEN ATTEMPTS TO HEAD SOUTHWEST
OVER SOUTH TEXAS AND INLAND OVER MEXICO. THE FEATURE WILL HAVE A
LITTLE HELP AS A MID LEVEL SHORT WAVE TROUGH DIGS INTO NORTH TEXAS
THROUGH FRIDAY...BUT ONCE THE TROUGH MOVES FARTHER EAST AND NORTH
THE TWO HEIGHT CENTERS WILL BEGIN TO FILL IN THE GAP OVER SOUTH
TEXAS...AND THE EASTERLY WAVE...IF IT IS STILL DISCERNIBLE LATE IN
THE WEEKEND...WILL MORE OR LESS BE ABSORBED. THE MID LEVEL TROUGH TO
THE NORTH WILL REMAIN BUT A PASSING COMET DRAGGING A TAIL...OR A
WEAK FRONT...ACROSS NORTH TEXAS AROUND SATURDAY WITH LITTLE REAL
IMPACT ON THE CWA. NONETHELESS...THE EASTERLY WAVE WILL BRING HIGH
PRECIPITABLE WATER VALUES...ABOVE TWO INCHES...INTO THE WEST GULF.
THUS...SHOWER ACTIVITY CONTINUING FROM WEDNESDAY INTO THE LONG TERM
WILL HAVE THE POTENTIAL TO DROP UP TO AN INCH OF RAIN IN A FEW
HOURS...WITH LOCALLY HEAVIER AMOUNTS POSSIBLE. THE BEST POTENTIAL
WILL BE THURSDAY AND FRIDAY AFTERNOONS...CONCURRENT WITH DAYTIME
HEATING...WITH ADDITIONAL ACTIVITY SATURDAY...BUT FARTHER INLAND.
ACTIVITY SHOULD DECREASE SUNDAY AND MONDAY AND TEMPERATURES AND HEAT
INDEX VALUES CREEP BACK UP A COUPLE OF DEGREES. EITHER WAY...TEMPS
WILL CONTINUE THE ABOVE NORMAL TENDENCY THROUGH THE LONG TERM.

FINALLY...A TROPICAL WAVE IN THE EASTERN CARIBBEAN LOOKS LIKE IT HAS
THE POTENTIAL TO TRANSLATE WEST TOWARD AND INTO THE BAY OF CAMPECHE
LATE IN THE WEEKEND AND INTO THE EARLY PART OF NEXT WEEK...WITH THE
MODELS HINTING AT A WEAK SURFACE LOW FORMING AT THAT TIME. BEYOND
SENDING A FEW SHOWERS NORTH MONDAY NIGHT INTO TUESDAY HOWEVER...AM
NOT LOOKING FOR SIGNIFICANT FURTHER DEVELOPMENT JUST YET. THUS...
THE MAIN GAME IN TOWN WILL BE THE EASTERLY WAVE OVER THE NORTHWEST
AND WEST GULF LATE THIS WEEK.

THE INHERITED FORECAST WAS IN PRETTY GOOD SHAPE. THE LONG RANGE
MODELS WERE IN REASONABLE AGREEMENT WITH THE UNFOLDING SCENARIO.
CHANGES WERE FEW. INCREASED POP CHANCES SLIGHTLY HERE AND THERE...
AS GUIDANCE NUMBERS TREND UP...BUT MAINTAINED CHANCE CATEGORY IN ALL
CASES.

MARINE...
NOW THROUGH THURSDAY...
A WEAK LOW PRESSURE SYSTEM WILL MOVE FROM THE WESTERN GULF OF MEXICO
INTO THE LOWER TEXAS COASTAL WATERS TODAY AND TONIGHT. THIS WILL
CAUSE AN INCREASE TO MORE MODERATE NORTHEASTERLY WINDS AND MAKE SEAS
SLIGHTLY MORE MODERATE THAN WHAT HAS BEEN EXPERIENCED THE LAST FEW
DAYS. WINDS MAY RISE TO EXERCISE CAUTION LEVELS THIS AFTERNOON AND
TONIGHT OUT OF THE NORTHEAST BEFORE SHIFTING TO THE EAST ON
THURSDAY. NUMEROUS SHOWERS AND THUNDERSTORMS ARE FORECAST STARTING
LATER TODAY AND PERSISTING THROUGH THURSDAY ON THE GULF WATERS WITH
MORE SCATTERED ACTIVITY ON THE LAGUNA AND VERY CLOSE TO THE COAST.

THURSDAY NIGHT THROUGH SUNDAY...A WEAK MID LEVEL INVERTED TROUGH
WILL LIE OVER EXTREME NORTHEAST MEXICO...AND WILL ALSO EXTEND NORTH
INTO SOUTH TX. THE TROUGH WILL COMBINE WITH AMPLE LOW LEVEL TROPICAL
MOISTURE TO PROLONG MARINE CONVECTION THROUGH THE LONG TERM. GIVEN
THAT THE WEAKNESS WILL REMAIN MORE OR LESS A FEATURE OVER SOUTH TX
BETWEEN HEIGHT CENTERS ON EITHER SIDE...A PERSISTENT AND UNSTABLE
MARINE ENVIRONMENT WILL BE THE RULE...WITH ONGOING SCATTERED SHOWERS
AND A FEW THUNDERSTORMS MOVING INTO AND ACROSS THE LOWER TX COASTAL
WATERS. LIGHT TO MODERATE SOUTH SOUTHEAST WINDS WILL INCREASE TO MDT
SATURDAY NIGHT THROUGH SUNDAY NIGHT AS HIGH PRESSURE BUILD INTO THE
GULF FROM THE EAST...AND SEAS WILL INCREASE TO BETWEEN 4 AND 6 FEET
OFFSHORE LATE IN THE LONG TERM...WITH POSSIBLE SMALL CRAFT EXERCISE
CAUTION CONDITIONS...ESPECIALLY FARTHER THAN A FEW MILES AWAY FROM
THE IMMEDIATE COAST.

&&

.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL  93  79  91  79 /  30  30  30  40
BROWNSVILLE          96  78  93  79 /  30  30  40  40
HARLINGEN            97  76  95  78 /  30  30  40  40
MCALLEN             100  79  98  79 /  10  20  40  40
RIO GRANDE CITY     101  79  99  79 /  10  10  30  40
SOUTH PADRE ISLAND   89  78  88  80 /  30  30  40  40

&&

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

$$

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