688
FXUS64 KBRO 181722 AAB
AFDBRO
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BROWNSVILLE TX
1222 PM CDT SUN AUG 18 2019
DISCUSSION
UPDATED FOR LATEST AVIATION DISCUSSION BELOW.
AVIATION
SATELLITE IMAGES AND SURFACE OBSERVATIONS INDICATE
STREAKS OF CUMULUS CLOUDS ACROSS THE EASTERN PORTIONS OF THE CWA
EARLY THIS AFTERNOON. CEILINGS WERE NEAR 4200FT AT KEBG TO NEAR
10000FT AT KTXW. EXPECT VFR CONDITIONS TO PREVAIL ACROSS THE RIO
GRANDE VALLEY THE REST OF THE AFTERNOON INTO THE EVENING AS THE
500MB SUBTROPICAL RIDGE ACROSS SOUTH TEXAS CONTINUES TO PROVIDE
SUBSIDENCE ACROSS THE AREA.
PREV DISCUSSION
/ISSUED 620 AM CDT SUN AUG 18 2019/
.12Z AVIATION UPDATE
DISCUSSION...UPDATED FOR LATEST AVIATION DISCUSSION BELOW.
AVIATION...VFR CONDITIONS WILL PREVAIL THROUGH THIS TAF CYCLE.
CAN'T RULE OUT A FEW LOW CLOUDS THROUGH THE MORNING HOURS,
HOWEVER, FLIGHT CATEGORIES SHOULD REMAIN UNCHANGED. THE ONLY STORY
WILL BE THE STRONG GUSTY WINDS DURING THE DAYLIGHT HOURS. EXPECT
SOUTHERLY WINDS TO INCREASE TO 20-25KTS IN GUSTS BEFORE DECREASING
SHORTLY AFTER SUNSET.
PREV DISCUSSION... /ISSUED BROWNSVILLE TX 343 AM CDT SUN AUG 18 2019/
SHORT TERM (TODAY THROUGH MONDAY): WITH THE H5 HIGH SITTING RIGHT
OVER THE REGION, PLENTY OF SUBSIDENCE WILL CONTINUE TO LIMIT
CLOUD/PRECIP THROUGH THE SHORT TERM PERIOD. TODAY SHOULD BE VERY
SIMILAR TO YESTERDAY, HOWEVER, SURFACE MOISTURE WILL BE JUST A BIT
HIGHER THAN THE LAST COUPLE OF DAYS. WITH THE INCREASE IN MOISTURE
AND TEMPERATURES HITTING CLOSE TO OR EXCEEDING THE 100 DEGREE MARK,
THE NEED FOR A HEAT ADVISORY IS THERE AS MANY LOCATIONS REACH 110-
115 DEGREE HEAT INDICES. WITH STRONG SURFACE HEATING, LOW LEVEL
MOISTURE WILL MIX OUT ACROSS ZAPATA AND JIM HOGG COUNTIES SO WE'LL
LEAVE THESE COUNTIES OUT OF THE ADVISORY FOR NOW AS HEAT INDEX
VALUES ONLY LOOK TO TOP OUT JUST BELOW ADVISORY THRESHOLDS.
WINDS WILL INCREASE ONCE AGAIN THIS AFTERNOON WITH CONTINUED
INTERACTION BETWEEN THE THERMAL SURFACE LOW UPSTREAM AND THE
SUBTROPICAL HIGH PRESSURE DOWNSTREAM. AFTERNOON BREEZES FROM 25 TO
30 MPH CAN'T BE RULED OUT, ESPECIALLY LOCATIONS CLOSER TO THE LAGUNA
MADRE. WITH SURFACE MOISTURE DECREASING ALONG AND WEST OF HIGHWAY
281, THERE WILL LIKELY BE AN UPTICK IN FIRE WEATHER POTENTIAL. AT
THIS TIME, RH VALUES WILL REMAIN ABOVE THRESHOLDS AND THE STRONGEST
WINDS WILL OCCUR LATER IN THE AFTERNOON AS LOW LEVEL MOISTURE BEGINS
TO INCREASE ONCE AGAIN.
THROUGH THE REMAINDER OF THE SHORT TERM, UPPER LEVEL RIDGE/HIGH WILL
CONTINUE TO BUILD WESTWARD TOWARD WESTERN PARTS OF TEXAS.
THIS WILL GRADUALLY ALLOW MOISTURE TO WORK BACK INTO THE COLUMN.
AT THIS POINT, IT LOOKS LIKE THERE WILL BE A GRADUAL UPTICK IN
RAINFALL CHANCES JUST OFFSHORE. WITH THE RIDGE MOVING WEST,
THICKNESSES DECREASE AND A FEW MORE CU WILL BE LIKELY THE MAX
TEMPERATURES SHOULD BE A DEGREE OR TWO LOWER...THOUGH STILL ABOVE
AVERAGE.
LONG TERM (MONDAY NIGHT THROUGH SATURDAY): WITH 500 MB RIDGING
ALOFT, SUBSIDENCE WILL REMAIN IN CONTROL THROUGH TUESDAY. WEDNESDAY
THROUGH THURSDAY IS MARKED BY A 500 MB LOW/INVERTED TROUGH THAT
NUDGES INTO DEEP SOUTH TEXAS, CAUSING THE 500 MB HIGH TO RETREAT TO
THE FOUR CORNERS REGION. THE WEAKNESS IN 500 MB HEIGHTS ALONG WITH
LOW TO MID LEVEL MOISTURE ADVECTION WILL BRING INCREASED CLOUD COVER
AND POPS INTO OUR CWA. AS SUCH, TEMPERATURES ARE EXPECTED TO DROP A
COUPLE OF DEGREES TO NEAR NORMAL AND BRING A LITTLE RESPITE FROM THE
OPPRESSIVE HEAT. BEST CHANCE OF SHOWERS AND THUNDERSTORMS WILL BE
ALONG THE COASTAL AREAS AND OFFSHORE WHERE MODELS KEEP THE MAJORITY
OF THE MOISTURE.
THURSDAY NIGHT INTO THE REST OF THE FORECAST PERIOD WILL DEPEND
PRIMARILY ON THE DEVELOPMENT OF A 500 MB CLOSED LOW IN THE WESTERN
GULF. THE ECMWF HAS THIS FEATURE SKIRT ALONG THE NORTHWESTERN GULF
ON FRIDAY AND KEEPS THE BULK OF THE LOW TO MID LEVEL MOISTURE
OFFSHORE. HOWEVER, THE GFS SHOWS THIS FEATURE TO BE LESS ORGANIZED
AND BRINGS THE MOISTURE FURTHER INLAND ACROSS OUR CWA AS IT MAKES
ITS TREK ALONG THE NORTHWESTERN GULF. REGARDLESS OF THE
DISCREPANCIES BETWEEN THE MODELS, BOTH ARE IN AGREEMENT WITH THE
INCREASED MOISTURE OVER OUR COASTAL REGION AND GULF WATERS FRIDAY,
SO HAVE INCREASED POPS A BIT FOR THIS AREA.
MARINE (TODAY THROUGH MONDAY): WITH THE PRESSURE GRADIENT BETWEEN
THE THERMAL LOW UPSTREAM AND BERMUDA HIGH DOWNSTREAM, CAUTIONARY
HEADLINES WILL LIKELY PERSIST ACROSS THE LAGUNA MADRE TODAY. GULF
WATERS WILL NEED CAUTIONARY HEADLINES IN CWF THIS MORNING AND ONCE
AGAIN THIS EVENING AND OVERNIGHT AFTER SUNSET AS THE STRONGER WINDS
SHIFT OFFSHORE. SEAS WILL BUILD TO AROUND 4 FEET OR SO AND REMAIN
ELEVATED THROUGH THE SHORT TERM PERIOD. TOWARD THE END OF THE
PERIOD, SCATTERED SHOWERS AND PERHAPS A FEW THUNDERSTORMS MAY BE
POSSIBLE AS TROPICAL MOISTURE BEGINS TO MOVE INTO THE REGION.
MONDAY NIGHT THROUGH THE REST OF THE PERIOD WILL SEE GRADUALLY
DECREASING WINDS AND SEAS AS THE PRESSURE GRADIENT WEAKENS
WEDNESDAY ACROSS THE DEEP SOUTH TEXAS COASTAL WATERS. MODERATE TO
LIGHT SOUTH TO SOUTHEAST WINDS WILL PERSIST THROUGH WEDNESDAY
AFTERNOON AND THEN BECOME GENERALLY LIGHT WHILE SEAS WILL TREND
FROM 3 TO 5 FEET ON TUESDAY TO 2 TO 4 FEET FOR THE REMAINDER OF
THE PERIOD. THROUGHOUT THIS PERIOD, THERE WILL BE A SLIGHT CHANCE
TO CHANCE OF SHOWERS AND THUNDERSTORMS OVER THE COASTAL GULF
WATERS.
BRO WATCHES/WARNINGS/ADVISORIES
TX...HEAT ADVISORY UNTIL 6 PM CDT THIS EVENING FOR TXZ250>257-351-353.
GM...NONE.
THIS PRODUCT IS ALSO AVAILABLE ON THE WEB AT:
HTTP://WEATHER.GOV/RGV
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