Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 200052 AAA
AFDSJU

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAN JUAN PR
852 PM AST FRI SEP 19 2014

.UPDATE...THE GFS MODEL AND THE MIMIC PRODUCT BOTH INDICATE A WEAK
WAVE OR TROUGH MOVING ACROSS PUERTO RICO FROM THE EAST AFTER
20/06Z THAT IS ALREADY AFFECTING THE U.S. VIRGIN ISLANDS. THIS IS
SHOWING UP AS SCATTERED SHOWERS WITH A FEW THUNDERSTORMS...MAINLY OVER THE
LOCAL WATERS FOR NOW...BUT THESE SHOWERS ARE EXPECTED TO CROSS THE
U.S. VIRGIN ISLANDS FROM TIME TO TIME AND ENTER INTO EASTERN
PUERTO RICO. THE MODEL ALSO DEPICTS A SECOND TROUGH OR WAVE
ENTERING ALMOST THE SAME TIME EARLY SUNDAY MORNING. IN BOTH CASES
MOISTURE IS EXPECTED TO LINGER...MAINLY IN THE INTERIOR AND
WESTERN PORTIONS OF PUERTO RICO. THE TUTT LOW THAT HAD ACTED AS A
FOCAL POINT FOR ACTIVITY YESTERDAY IS NOW ALMOST COMPLETELY
DISSIPATED AND WILL PLAY ONLY A VERY MINOR ROLE IN THE CONVECTION
SATURDAY AND SUNDAY. BY MONDAY THERE WILL BE A VERY WEAK EAST-WEST
RIDGE OVER THE AREA AT UPPER LEVELS.

&&

.DISCUSSION...MODELS ARE CONTINUING TO SHOW A TREND IN ELIMINATING
A TROPICAL WAVE TO CROSS ON MONDAY IN FAVOR OF SEVERAL SMALL WAVES
CROSSING THROUGH LATE TONIGHT AND EARLY SUNDAY MORNING. FLOW
MONDAY THROUGH THURSDAY AT 700 MB APPEARS TO FLATTEN
OUT...LEAVING ONLY GOOD MOISTURE IN ITS PLACE. THE GFS NOW SHOWS
PRECIPITABLE WATER REACHING A WEAK PEAK ON SATURDAY AFTERNOON AND A
MAXIMUM OVER 2 INCHES ON SUNDAY AFTERNOON WITH AN INTERVENING
DRIER SLOT OF AIR SATURDAY NIGHT. AFTER SUNDAY AFTERNOON MOISTURE
DIMINISHES STEADILY THROUGH TUESDAY MORNING TO AS LITTLE AS 1.65 INCHES.
MOISTURE GRADUALLY IMPROVES THROUGH THURSDAY AFTERNOON WITH A
SERIES OF RIPPLES IN THE FLOW OUT OF THE CENTRAL ATLANTIC CREATING
MORE SHOWERS IN THE NORMAL DIURNAL PATTERN OF SHOWERS ACROSS THE
ISLANDS.

&&

.AVIATION...PASSING SHRA AND ISOLD TSRA ACTIVITY IS EXPECTED TO
CONTINUE OVERNIGHT UNTIL 20/16Z...POSSIBLY AFFECTING
TJSJ...TIST...TISX...TNCM...AND TKPK BRIEFLY WITH VCSH LIKELY FOR
THOSE TERMINALS. AFTER 20/16Z...SHRA/TSRA DEVELOPMENT ACROSS CENTRAL
AND WESTERN PR WILL CAUSE MTN OBSCURATIONS AND AFFECT TJMZ AND
TJBQ. EASTERLY SFC WINDS WILL PREVAIL OVERNIGHT AT ABOUT 5-10 KTS
INCREASING SLIGHTLY AFTER 20/12Z WITH SEA BREEZE VARIATIONS. TOPS
LATE THIS EVENING HAVE BEEN OBSERVED UP TO 46 KFT.

&&

.MARINE...WITH TRADE WINDS MODERATE AT BEST AND NO STRONG STORMS
IN THE ATLANTIC EXPECT LITTLE CHANGE IN THE MARINE CONDITIONS.
SOME THUNDERSTORMS AND GUSTY WINDS MAY BE ENCOUNTERED AS THE
TROUGHS MOVE THROUGH THE AREA OTHERWISE EXPOSED WATERS SHOULD SEE
NO MORE THAN 3 TO 5 FOOT SEAS FOR AT LEAST THE NEXT 7 DAYS.


&&

.PREV DISCUSSION... /ISSUED 242 PM AST FRI SEP 19 2014/

SYNOPSIS...TUTT LOW WILL CONTINUE TO MEANDER OVER THE NORTHEAST
CARIBBEAN DURING THE NEXT FEW DAYS. AS TROPICAL WAVE ACROSS THE
MONA PASSAGE MOVES FURTHER WEST...WEATHER CONDITIONS WILL CONTINUE
TO IMPROVE ACROSS THE LOCAL ISLANDS. THE NEXT TROPICAL WAVE
PASSAGE IS EXPECTED ON MONDAY.

DISCUSSION...AS TROPICAL WAVE ACROSS THE MONA PASSAGE CONTINUES
TO MOVE FURTHER WEST....WEATHER CONDITIONS WILL CONTINUE TO IMPROVE
ACROSS THE LOCAL ISLANDS. ALTHOUGH...POTENTIAL FOR ADDITIONAL
SHOWERS AND THUNDERSTORMS LATE THIS AFTERNOON AND EARLY IN THE
EVENING WILL PERSIST MAINLY OVER THE CORDILLERA AND W PR.

MEANDERING TUTT LOW ACROSS THE AREA...WILL CONTINUE TO ENHANCE TRADE
WIND SHOWERS ACROSS THE EASTERN CARIBBEAN WITH SOME OF THEM REACHING
USVI AND E PR LATE THIS EVENING AND SATURDAY MORNING. SATURDAY
AFTERNOON THROUGH AT LEAST MONDAY...A MORE TYPICAL WEATHER PATTERN
WILL PREVAIL ACROSS THE LOCAL ISLANDS WITH A FEW PASSING SHOWERS
ACROSS USVI AND E PR IN THE MORNING FOLLOWED BY AFTERNOON CONVECTION
ACROSS THE CORDILLERA AND WEST PUERTO RICO IN THE AFTERNOON. SOME
OF THESE AFTERNOON SHOWERS AND THUNDERSTORMS MAY BECOME STRONG AS
TUTT AXIS MOVES WEST OF PR.

ANOTHER TROPICAL WAVE AND ASSOCIATED AREA OF LOW PRESSURE NEAR 48
WEST WILL CONTINUE WESTWARD...AND APPROACH THE LESSER ANTILLES
SUNDAY. IT IS TO THEN FORECAST TO ENTER AND MOVE ACROSS THE
EASTERN CARIBBEAN LATE SUNDAY AND INTO MONDAY...INCREASING ONCE
AGAIN THE CHANCE OF SHOWERS AND THUNDERSTORMS.

AVIATION...SHRA/TSRA ACTIVITY IS EXPECTED TO CONTINUE OVER CENTRAL
AND WESTERN PR UNTIL AROUND 19/23Z...WITH MVFR/IFR CONDS AND
MOUNTAIN OBSCURATION. VCSH/VCTS POSSIBLE FOR ISLAND AND TJSJ TAF
SITES THROUGH THE NIGHT. WINDS E TO SE OF 10-15 KT WILL PREVAIL
BELOW FL150...WITH HIGHER GUSTS AROUND 30 KT NEAR TSRA.

MARINE...MARINE CONDITIONS WILL CONTINUE MAINLY 5 FEET OR LESS WITH
WINDS GENERALLY UP TO 17 KNOTS TONIGHT. LOCALLY HEAVY RAINFALL AND
STRONG GUSTY WINDS ARE POSSIBLE WITH ANY THUNDERSTORM THAT
DEVELOPS ACROSS THE WATERS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  78  88  79  88 /  40  40  30  30
STT  78  89  78  89 /  50  50  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...NONE.
&&

$$

25/12




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