066  
FXCA62 TJSJ 170134  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
934 PM AST WED JAN 16 2019  
   
UPDATE
 
 
MODERATE TO HEAVY RAINFALL FELL ACROSS PORTIONS OF ARECIBO THIS  
EVENING, WHICH CAUSED A FLASH FLOOD ADVISORY TO BE ISSUED FOR THE  
AREA. THE SEA BREEZE DEVELOPED LATE THIS AFTERNOON AND ENHANCED  
SHOWERS ACTIVITY ACROSS EASTERN, INTERIOR AND NORTHERN AREAS OF  
PUERTO RICO. ADDITIONALLY LOW-LEVEL MOISTURE ALSO AIDED IN SHOWER  
DEVELOPMENT.  
 
MOISTURE IS FORECAST TO INCREASE TOMORROW AND FINALLY REACH A  
PEAK LATE FRIDAY. THEREFORE, EXPECT SHOWERS ACTIVITY TO INCREASE  
TOMORROW THROUGH FRIDAY AS A RESULT OF INCREASING MOISTURE.  
HOWEVER, SHOWERS WILL BE SHORT-LIVED DUE TO DRIER AIR THAT WILL  
BE IN THE MID AND UPPER LEVELS OF THE ATMOSPHERE. THE DRIER WILL  
LIMIT VERTICAL DEVELOPMENT OF SHOWERS OVER THE AREA, THUS SHOWERS  
ARE EXPECTED TO BE SHORT-LIVED.  
 

 
 
   
AVIATION
 
 
VRF CONDS ARE FORECAST TO CONTINUE ACROSS MOST TERMINAL SITES  
THROUGH 17/12Z, BUT +SHRA COULD CAUSE SOME TERMINAL SITES TO FALL  
BRIEFLY TO MVRF CONDS. MOISTURE OVER THE AREA IS CAUSING +RA OVER  
PORTIONS OF EASTERN AND CENTRAL PUERTO RICO. SHRA ARE POSSIBLE  
ACROSS THE LOCAL TERMINALS DURING THE OVERNIGHT AND EARLY MORNING  
HOURS, ESPECIALLY FOR TERMINALS TJSJM TIST, AND TISX. SFC WINDS  
WILL BE OUT OF THE EAST AT 5 TO 10 KTS, WIND BRIEFLY TURN TO THE  
SOUTHEAST AT 014 TO 016 KFT, THEN WIND TURN TO THE WEST TO  
NORTHWEST AT 024 TO 046 KFT WITH WINDS RANGING FROM 30 TO 60 KTS.  
 

 
   
MARINE
 
 
SEAS WILL REMAIN BETWEEN 3 TO 5 FEET ACROSS MOST OF THE LOCAL  
WATERS THROUGH FRIDAY. A NORTHERLY SWELL WILL CONTINUE TO MOVE  
INTO THE AREA THROUGH FRIDAY, THUS INCREASING RISK OF RIP  
CURRENTS TO HIGH FROM THE COASTLINE OF ARECIBO TO CAROLINA ON  
THURSDAY MORNING.  
 

 
   
PREV DISCUSSION
 
/ISSUED 423 PM AST WED JAN 16 2019/  
 
SYNOPSIS...  
TRADE WINDS BROUGHT A SURGE OF MOISTURE ACROSS THE ISLANDS TODAY.  
THE SOUTH-SOUTHEAST STEERING WIND FLOW SUPPORTED THE DEVELOPMENT  
OF SHOWERS ALONG AND TO THE NORTH OF THE CORDILLERA CENTRAL THIS  
AFTERNOON. MOISTURE ADVECTION WILL CONTINUE ACROSS THE AREA AND  
PREVAIL THROUGH THE WEEKEND. LACK OF UPPER LEVEL SUPPORT WILL  
SUPPRESS ANY VERTICAL DEVELOPMENT LIMITING RAINFALL ACCUMULATIONS  
THROUGH THE FORECAST PERIOD.  
 
SHORT TERM...TONIGHT THROUGH FRIDAY...  
 
A SURGE OF MOISTURE AND SOUTH-SOUTHEAST STEERING WIND FLOW AID IN  
THE DEVELOPMENT OF SCATTERED SHOWERS ALONG AND TO THE NORTH OF  
THE CORDILLERA CENTRAL THIS AFTERNOON. THIS ACTIVITY WILL CONTINUE  
THROUGH THIS EVENING. RAINFALL ACCUMULATIONS WILL BE MINIMAL DUE  
TO THE LACK OF UPPER LEVEL SUPPORT. RAINFALL ACTIVITY WILL SLOWLY  
DIMINISH ACROSS THE NORTH AND WESTERN SECTIONS OF PUERTO RICO LATE  
TONIGHT, WHILE THE WINDWARD SECTIONS OF U.S. VIRGIN ISLANDS AND  
PUERTO RICO WILL CONTINUE TO OBSERVE BRIEF PASSING SHOWERS AT  
TIMES. THE SOUTHERN SLOPES OF PUERTO RICO COULD EXPECT MOSTLY  
CLEAR SKIES WITH NO SHOWER ACTIVITY.  
 
SATELLITE IMAGERY DETECTED ANOTHER SURGE OF MOISTURE WHICH MODEL  
GUIDANCE SUGGEST ITS ARRIVAL ACROSS THE U.S. VIRGIN ISLANDS AND  
EASTERN PUERTO RICO AFTER MIDNIGHT INTO FRIDAY MORNING. SHOWERS  
WILL AFFECT THESE AREAS, WHILE THE REST OF PUERTO RICO WILL HAVE  
MOSTLY CLEAR SKIES. BY FRIDAY AFTERNOON, A SURFACE PERTURBATION  
WILL INTERACT WITH THIS MOISTURE INDUCING AFTERNOON SHOWERS ACROSS  
AND TO THE WEST OF THE CORDILLERA CENTRAL. SOME SHOWERS SHOULD NOT  
BE RULED OUT OVER THE SAN JUAN METRO AREA. AN ADVECTIVE PATTERN  
WILL CONTINUE ON FRIDAY AS ADDITIONAL CLOUDS AND SHOWERS WILL  
CONTINUE TO MOVE ACROSS THE ISLANDS.  
 
LONG TERM...SATURDAY THROUGH WEDNESDAY...PREVIOUS DISCUSSION.  
 
ENOUGH LOW-LEVEL MOISTURE WILL REMAIN PRESENT ON SATURDAY TO  
RESULT IN BRIEF PASSING SHOWERS ACROSS PORTIONS OF EASTERN PUERTO  
RICO AND THE USVI DURING THE MORNING HOURS. THIS WILL BE FOLLOWED  
BY THE DEVELOPMENT OF LOCALLY AND DIURNALLY INDUCED SHOWERS  
ACROSS INTERIOR AND WESTERN PORTIONS OF PUERTO RICO DURING THE  
MID TO LATE AFTERNOON HOURS.  
 
AS THE AFORMENTIONED MID TO UPPER-LEVEL RIDGE AMPLIFIES OVERHEAD  
LATE IN THE WEEKEND THROUGH THE FIRST PART OF NEXT WEEK, THE LOW-  
LEVEL MOISTURE IS EXPECTED TO GRADUALLY ERODE. THIS WILL RESULT IN  
MAINLY FAIR WEATHER CONDITIONS WITH VERY LIMITED SHOWER ACTIVITY  
EXPECTED ACROSS THE REGION. BY THE MIDDLE OF NEXT WEEK, MODEL  
GUIDANCE IS SUGGESTING AN INCREASE IN THE WINDS FROM THE NORTHEAST  
AS A STRONG SURFACE HIGH PRESSURE MOVES OFF THE NORTHEAST COAST  
OF THE UNITED STATES INTO THE WESTERN ATLANTIC, TIGHTENING THE  
PRESSURE GRADIENT SOMEWHAT.  
 
AVIATION...VFR CONDITIONS EXPECTED ACROSS THE LOCAL TERMINALS  
THROUGH THE FORECAST PERIOD. HOWEVER, SHRA MAY RESULT IN BRIEF MVFR  
CONDITIONS AT TJMZ THROUGH 17/00Z. AFTERNOON CONVECTION WILL ALSO  
BRING VCSH TO TJBQ, TJPS AND TJSJ THROUGH 16/22Z. AS PATCHES OF  
MOISTURE MOVE ACROSS THE REGION, VCSH ARE EXPECTED AT TIST, TISX,  
TNCM AND TKPK, PARTICULARLY BETWEEN 16/22Z AND 17/14Z. SURFACE WINDS  
WILL CONTINUE FROM THE EAST SOUTHEAST AT AROUND 10-15KT WITH SEA  
BREEZE VARIATIONS THROUGH 16/22Z, BECOMING LIGHT AND VARIABLE  
OVERNIGHT.  
 
MARINE...  
TRANQUIL MARINE CONDITIONS ARE EXPECTED TO CONTINUE ACROSS THE  
REGIONAL WATERS THROUGH THE FORECAST PERIOD. WINDS AROUND 15 KNOTS  
WILL VEER FROM THE EAST-SOUTHEAST THROUGH AT LEAST FRIDAY, WHEN  
THE TYPICAL EASTERLY TRADE ARE FORECAST TO RETURN. SEAS WILL RANGE  
BELOW 5 FEET. A NORTHERLY SWELL IS MOVING ACROSS THE ATLANTIC  
WATERS AND WILL CONTINUE THROUGH AT LEAST SATURDAY.  
 
THERE IS A MODERATE RIP CURRENT RISK FOR A FEW BEACHES ALONG THE  
NORTH COAST OF PUERTO RICO. ELSEWHERE, A LOW RIP CURRENT RISK IS  
IN EFFECT. A HIGH RISK OF RIP CURRENTS IS FORECAST FOR SOME NORTH  
FACING BEACHES OF PUERTO RICO TOMORROW.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SJU 71 84 72 84 / 40 30 10 20  
STT 72 84 71 84 / 40 40 30 30  
 

 
   
SJU WATCHES/WARNINGS/ADVISORIES
 
 
PR...HIGH RIP CURRENT RISK FROM 6 AM AST THURSDAY THROUGH LATE  
THURSDAY NIGHT FOR NORTH CENTRAL-SAN JUAN AND VICINITY.  
 
VI...NONE.  
AM...NONE.  

 
 

 
 
SHORT TERM...99  
LONG TERM....99  
 
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