Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 171547
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1147 AM AST THU APR 17 2014

.UPDATE...INCREASING CLOUDINESS ACROSS THE REGION ACCOMPANYING WEAK
EASTERLY MOISTURE SURGE MOVING ACROSS THE REGION TODAY. LOCAL SHIP...BUOY
AND SURFACE OBSERVATIONS...AS WELL AS DOPPLER WEATHER RADAR VELOCITY
PRODUCTS SUGGESTS WIND GUST OF UP TO 30 MPH POSSIBLE WITH THE PASSING
SHOWER ACTIVITY. RECENT TJSJ 17/12Z UPPER AIR SOUNDING SHOWED MOST
OF MOISTURE TRAPPED BELOW 700 MILLIBARS...AS RIDGE ALOFT WILL REMAIN
IN PLACE AND MAINTAIN REGION ON SUBSIDENCE/CONVERGENT SIDE OF TUTT
WHICH WILL LINGER ACROSS THE LESSER ANTILLES AND EAST OF THE REGION
THROUGH THE END OF THE WEEK AND INTO THE WEEKEND. NO CHANGES MADE
TO THE INHERITED SHORT TERM FORECAST PACKAGE AT THIS TIME.

&&

.AVIATION UPDATE...SCT-BKN LOW TO MID LVL CLD SPREADING WESTWARD
ACROSS THE FCST AREA FM THE LESSER ANTILLES WITH EMBEDDED -SHRA/SHRA.
EXPECT THESE SHOWERS TO AFFECT MOST TAF SITES FROM TIME TO TIME
DUE TO PASSING SHOWERS AT LEAST UNTIL 17/22Z. BRIEF PRD OF MVFR IN
SHRA/LOW CIG WITH SFC WND GUST UP TO 26 KTS PSBL AT ALL TAF SITES.
MTN TOP OBSCR WILL REMAIN PSBL MAINLY ACROSS PICO DEL ESTE PR...AND
THE REST OF THE CENTRAL MTN RANGE...MAINLY FM 17/17Z-17/22Z. LOW
LEVEL WNDS MAINLY FM E AT 15-20 KTS BLO FL150...BCMG FM N-NW AND
INCR W/HT ABV TO MAX WND OF AROUND 60 KTS OR SO NR FL400.

VISITORS AND LOCAL BEACH GOERS ARE URGED TO BE ALERT AND BE CAUTIOUS
DURING THE NEXT FEW DAYS...SUSTAINED WINDS UP TO 20 MPH WITH OCCASIONAL
HIGHER GUSTS ARE EXPECTED OVER THE COASTAL WATERS AND ALONG THE COASTAL
SHORELINES. THIS WILL RESULT IN CHOPPY AND HAZARDOUS SURF ZONE CONDITIONS.
IN ADDITION...THESE WINDS WILL ENHANCE AND GENERATE DANGEROUS RIP CURRENTS
ESPECIALLY ALONG THE NORTH AND EAST FACING BEACHES.

&&

.MARINE UPDATE...MODERATE TO LOCALLY FRESH TRADE WINDS OF 15 TO 20
KNOTS CONTINUED ACROSS THE REGIONAL WATERS WITH OCCASIONALLY HIGHER
GUSTS UP TO 26 KNOTS OR SO ACCOMPANYING QUICK PASSING SHOWERS.
LOCAL WINDS ARE EXPECTED TO STRENGTHEN ACROSS THE REGIONAL WATERS
THROUGH AT LEAST SATURDAY AS THE SURFACE PRESSURE GRADIENT TIGHTENS.
THEREFORE SMALL CRAFT ADVISORIES WILL REMAIN IN EFFECT FOR MOST OF
THE ATLANTIC WATERS AND LOCAL PASSAGES THROUGH SATURDAY. SMALL
CRAFT OPERATORS SHOULD EXERCISE CAUTION ACROSS THE LOCAL CARIBBEAN
WATERS THIS MORNING BUT A SMALL CRAFT ADVISORY WILL GO INTO EFFECT
FOR THESE WATERS THIS AFTERNOON. PLEASE REFER TO THE LATEST COASTAL
WATERS FORECAST AND MARINE WEATHER MESSAGE ISSUED BY THE WFO SAN
JUAN OFFICE PR.


&&

.PREV DISCUSSION... /ISSUED 529 AM AST THU APR 17 2014/

SYNOPSIS...AT UPPER LEVELS...ALTHOUGH STRONG LOW PRESSURE 2700
MILES NORTHEAST OF THE AREA PULLS AWAY ON SATURDAY ANOTHER WEAK
CUT-OFF LOW FORMS ABOUT 1000 MILES NORTHEAST AND DROPS INTO THE
WESTERN TROPICAL ATLANTIC LATE SUNDAY. THIS KEEPS A RIDGE WEST OF
PUERTO RICO AND THE U.S. VIRGIN ISLANDS UNTIL IT PASSES THROUGH ON
SUNDAY. A TROUGH MOVES THROUGH LATE NEXT WEEK.

AT MID LEVELS...A TROUGH EXTENDS INTO THE EASTERN CARIBBEAN FROM A
STRONG LOW 2700 MILES NORTHEAST OF THE AREA. HIGH PRESSURE HAS
CONTINUED OVER THE WESTERN AND CENTRAL CARIBBEAN. HIGH PRESSURE IN
THE EASTERN TROPICAL ATLANTIC WILL RIDGE ACROSS AND CONNECT TO THE
HIGH IN THE CARIBBEAN NEXT WEEK.

AT LOWER LEVELS...HIGH PRESSURE IN THE NORTHWEST CENTRAL ATLANTIC
WILL DRIFT SOUTH AND WEAKEN NOW THROUGH TUESDAY. A LOW PRESSURE IN
THE GULF OF MEXICO ON FRIDAY WILL JOIN THE WEAKNESS OFF THE
EASTERN COAST OF THE UNITED STATES OVER THE WEEKEND AND MOVE
NORTHEAST EARLY NEXT WEEK. LOW LEVEL WINDS WILL TURN SOUTHERLY
EARLY NEXT WEEK AND THE TRAILING TROUGH WILL MOVE THROUGH THE AREA
LATE NEXT WEEK.

DISCUSSION...SHOWER ACTIVITY INCREASED CONSIDERABLY OVER THE
LOCAL WATERS AND BROUGHT MEASURABLE RAINS TO THE FOOTHILLS ON THE
NORTHERN AND EASTERN COASTS. AMOUNTS WERE GENERALLY LIGHT. THE
GFS INCREASED THE AMOUNT OF PRECIPITABLE WATER EXPECTED OVER AREA
TODAY FROM YESTERDAYS SOLUTION AND THIS ALSO REPRESENTS MORE
MOISTURE THAN WAS SEEN YESTERDAY. THEREFORE EXPECT SHOWERS TO
FORM OVER THE CORDILLERA CENTRAL FIRST AND THEN MUCH OF WESTERN
AND INTERIOR PUERTO RICO AND TO COVER MORE AREA AND YIELD MORE
RAINFALL THAN YESTERDAY. WINDS WILL SHIFT FROM SLIGHTLY EAST
NORTHEAST TO SLIGHTLY EAST SOUTHEAST DURING THE DAY AND SO EXPECT
BETTER RAINFALL COVERAGE OF THE NORTHWEST PORTION OF PUERTO RICO
THIS AFTERNOON THAN WAS EXPERIENCED YESTERDAY. AS WITH
YESTERDAY...SOME SHOWERS ARE EXPECTED TO LINGER INTO THE EVENING
TONIGHT AS WELL. MOISTURE PEAKS THIS AFTERNOON...BUT THE GFS NOW
SHOWS A SECONDARY MOISTURE PEAK FRIDAY MORNING...THEREFORE EXPECT
GOOD SHOWER COVERAGE AROUND THE LOCAL ISLANDS OVERNIGHT TONIGHT.
THIS MOISTURE IS ALSO CONSIDERABLY DEEPER...WITH 50 PERCENT
RELATIVE HUMIDITY NOW AS HIGH AS 18K FT. MOISTURE REACHES A
MINIMUM OVERNIGHT ON FRIDAY AND THEN RATCHETS BACK UP THROUGH
WEDNESDAY NIGHT. SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED
TO RETURN TO THE AREA SUNDAY AND LAST THROUGH AT LEAST THE
FOLLOWING THURSDAY. FOR MOST AREAS THIS SHOULD GREATLY AMELIORATE
THE DRIER THAN NORMAL CONDITIONS EXPERIENCED SO FAR THIS MONTH.
DUE TO THE PREVAILING RIDGE...THE UPPER LEVELS WILL NOT CONTRIBUTE
TOO MUCH TO THE DEVELOPMENT OF THUNDERSTORMS...BUT A SLIGHT CHANCE
HAS BEEN INCLUDED IN THE FORECAST TODAY AND FRIDAY BECAUSE THE
MOISTURE IN THE SOUNDING WILL ALLOW CLOUDS TO GROW MORE DEEPLY
DESPITE THE RELATIVELY STABLE ATMOSPHERE. NEXT WEEK CONDITIONS
WILL BE EVEN MORE FAVORABLE.

AVIATION...AS AN AREA OF MOISTURE CONTINUES TO MOVE WESTWARD ACROSS
THE LEEWARD ISLANDS INTO EASTERN PR EARLY THIS MORNING...PASSING
SHOWERS AND BRIEF MVFR CIGS ARE POSSIBLE IN AND AROUND
TJSJ...TIST...TISX...TNCM AND TKPK. AFTER 17/16Z...SHRA WILL DEVELOP
ONCE AGAIN ACROSS THE CENTRAL INTERIOR AND WESTERN PR RESULTING IN
MVFR CONDITIONS AFFECTING TJMZ AND MOUNTAIN OBSCURATIONS ISLAND-WIDE.
WINDS WILL BE EAST 15-20 KTS FM THE SFC TO AROUND 10 KFT.

MARINE...SEAS HAVE BEGUN TO RISE AND BUOY 41043 HAS NOW REACHED
7.5 FEET SEVERAL TIMES OVERNIGHT. THEREFORE THE INITIAL SMALL
CRAFT ADVISORY FOR THE OUTER ATLANTIC WATERS WAS MOVED UP TO 9 AM
AST THIS MORNING. SEAS WILL REMAIN HAZARDOUS THROUGH SUNDAY IN
MOST UNPROTECTED WATERS OF THE FORECAST AREA.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  85  75  86  75 /  50  60  50  30
STT  84  75  85  76 /  50  60  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 6 AM AST SUNDAY
     FOR ANEGADA PASSAGE SOUTHWARD TO 17N-CARIBBEAN WATERS OF
     PUERTO RICO FROM 10 NM TO 17N-COASTAL WATERS OF NORTHERN
     USVI AND CULEBRA OUT 10 NM-COASTAL WATERS OF SOUTHERN USVI
     VIEQUES AND EASTERN PUERTO RICO OUT 10 NM.

     SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 6 AM AST SUNDAY
     FOR COASTAL WATERS OF NORTHERN PUERTO RICO OUT 10 NM-MONA
     PASSAGE SOUTHWARD TO 17N.

     SMALL CRAFT ADVISORY FROM 3 PM FRIDAY TO 6 AM AST SUNDAY FOR
     COASTAL WATERS OF NORTHWESTERN PUERTO RICO OUT 10 NM.

     SMALL CRAFT ADVISORY UNTIL 6 AM AST SUNDAY FOR ATLC WATERS OF
     PUERTO RICO AND USVI FROM 10NM TO 19.5N.

&&

$$

09/64





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