Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 180208 AAA
AFDSJU

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SAN JUAN PR
1008 PM AST FRI APR 17 2015

.SYNOPSIS...THE 18/00Z SOUNDING CAME IN WITH ALMOST 1.5 INCHES OF
PRECIPITABLE WATER. WINDS ARE ALREADY SHOWING THE SHIFT TO
SOUTHEAST AT THE SURFACE AND SOUTH SOUTHEAST AT 850 MB WITH LIGHT
WINDS UP TO 25 KFT. SHOWERS ARE STILL MOVING TOWARD THE WEST
NORTHWEST BUT ARE BEGINNING TO PENETRATE A LITTLE FURTHER INLAND
OVER EASTERN PUERTO RICO AND HAVE FORMED A STREAM OF SHOWERS
ISSUING FROM OFFSHORE FROM VEGA BAJA THAT LOOKS LIKE IT WILL
PERSIST FOR AT LEAST ANOTHER SEVERAL HOURS. SHOWERS ARE ALSO
MOVING ACROSS SAINT CROIX THIS EVENING THOUGH AMOUNTS ARE
GENERALLY LIGHT.

&&

.DISCUSSION...THE UPPER LEVEL TROUGH IS FAIRLY WEAK...BUT THERE
IS A PATCH OF MOISTURE APPROACHING THE U.S. VIRGIN ISLANDS AND
PUERTO RICO THAT WILL BRING ANOTHER ROUND OF SHOWERS TONIGHT
ACCORDING TO THE MIMIC PRODUCT AND TOMORROW ACCORDING TO THE 850
MB RH VALUES...AND THE GFS FORECAST PRECIPITABLE WATER WHICH WILL
INCREASE A LITTLE MORE TOMORROW AFTERNOON. THE GFS IS ALSO
FORECASTING STRONG DIVERGENCE OVER MOST OF PUERTO RICO CENTERED
OVER LAGUNA SAN JOSE AT 18/18Z. AM TAKING THIS TO MEAN THAT THERE
IS A POSSIBILITY OF A STREAMER OFF OF EL YUNQUE WITH MODERATE TO
HEAVY RAIN. WINDS ARE NOT WELL ALIGNED FROM THE SURFACE THROUGH
700 MB...SO WILL ASSIGN RELATIVELY LOW CONFIDENCE IN THIS FOR
NOW...BUT HAVE RAISED THE POP FROM EL YUNQUE TO BAYAMON AS A
PRECAUTION.

&&

.AVIATION...MOSTLY VFR CONDITIONS EXPECTED ACROSS THE LOCAL FLYING
AREA DURING THE FORECAST PERIOD. HOWEVER...VCSH POSSIBLE ACROSS
TISX...TIST AND TJSJ AS WELL AS ACROSS TNCM AND TKPK DURING THE
OVERNIGHT HOURS AS SCT SHRA MOVES THROUGH THE LOCAL AREA. SHRA/TSRA
DEVELOPING ACROSS THE NW QUADRANT OF PR AFTER 18/17Z MAY CAUSE AT
LEAST VCSH/VCTS WITH POSSIBLE MVFR CONDS DUE TO REDUCED VISIBILITY
AND CEILINGS AT TJMZ AND TJBQ.

&&

.MARINE...CONDITIONS REMAIN BELOW SMALL CRAFT ADVISORY LEVELS
THROUGH NEXT WEEK...BUT SMALL CRAFT WILL NEED TO EXERCISE CAUTION
ALONG THE NORTH AND SOUTH COASTS FOR WINDS FOR THE NEXT SEVERAL
DAYS. SEAS MAY REACH 6 FEET IN THE NORTHEASTERN LOCAL OUTER
ATLANTIC WATERS LATER NEXT WEEK IN THE CURRENT OUTLOOK.

&&

.PREV DISCUSSION... /ISSUED 259 PM AST FRI APR 17 2015/

SYNOPSIS...UPPER LEVEL TROUGH IS EXPECTED TO HOLD INTO SUNDAY AS
UPPER LEVEL RIDGE BUILDS ONCE AGAIN EARLY NEXT WEEK. SURFACE
HIGH PRESSURE MOVING INTO THE CENTRAL ATLANTIC WILL CONTINUE TO
PROMOTE MODERATE EASTERLY TRADE WINDS ACROSS THE REGION. THE WINDS
WILL SHIFT FROM THE SOUTHEAST DURING THE WEEKEND AS THE HIGH
PRESSURE MOVES INTO THE CENTRAL AND EASTERN ATLANTIC.

DISCUSSION...SHOWERS AND THUNDERSTORMS DEVELOPED BY EARLY
AFTERNOON ALONG THE CORDILLERA CENTRAL AND WESTERN PUERTO RICO.
BY 2 PM...THE DOPPLER RADAR ESTIMATED AROUND 2 INCHES OF RAIN OVER
SECTIONS OF YAUCO...VILLALBA AND MOCA. SHOWERS SHOULD CONTINUE
AT LEAST UNTIL SUNSET...WITH A FEW OF THEM MAINLY OVER WESTERN PR
THRU THE EARLY EVENING HOURS. SATELLITE IMAGERY SUGGESTS A WEAK INDUCED
LOW LEVEL TROUGH ACROSS THE NORTHEASTERN CARIBBEAN. MODEL GUIDANCE
INDICATES THAT THE DISTURBANCE SHOULD CONTINUE TO MOVE WITH THE
SOUTHEASTERLY WIND FLOW INTO THE ATLANTIC WATERS.

THE UPPER LEVEL TROUGH WILL INCREASE MOISTURE AND INSTABILITY
WITH BETTER CHANCE FOR ENHANCED SHOWER ACTIVITY ACROSS THE ISLANDS
AND COASTAL WATERS AT LEAST UNTIL MONDAY. LESSER ACTIVITY IS
EXPECTED BY MID WEEK AS THE UPPER LEVEL RIDGE BUILDS ACROSS THE
REGION FROM THE WEST ONCE AGAIN PLACING THE AREA ON THE
CONVERGENT/SUBSIDENT SIDE OF WEAKENING UPPER TROUGH. AS THE RIDGE
BUILDS ALOFT INTO EARLY NEXT WEEK...THE FREQUENCY AND AREAL
COVERAGE OF SHOWER AND THUNDERSTORM ACTIVITY WILL DECREASE AND
ALLOW FOR MOSTLY FAIR WEATHER SKIES TO PREVAIL ONCE AGAIN.

AVIATION...SHOWERS AND POSSIBLE T-STORM IN THE VCNTY OF TJBQ AND
TJMZ THRU 22Z WITH MVFR CIGS AND AGAIN ON SAT MAINLY AT TJBQ.
OTHERWISE...VFR CONDITIONS WITH WINDS BECOMING MORE SOUTHEAST.

MARINE...SMALL CRAFT SHOULD CONTINUE TO EXERCISE CAUTION ACROSS
THE CARIBBEAN WATERS DUE TO WINDS UP TO 20 KNOTS. IN GENERAL
EXPECT SEAS OF 5 FEET OR LESS TO CONTINUE FOR THE NEXT SEVERAL
DAYS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  74  88  74  89 /  40  30  40  40
STT  77  84  77  85 /  30  30  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
AM...NONE.
&&

$$

25/12



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