889  
FXCA62 TJSJ 230039  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
839 PM AST THU AUG 22 2019  
   
UPDATE
 
FORECAST REMAINS ON TRACK. LINGERING LOW-LEVEL MOISTURE  
ASSOCIATED WITH A DEPARTING WEAK TROPICAL WAVE WILL PERSIST OVER  
THE AREA THROUGH FRIDAY. THIS WILL RESULT IN SOME PASSING SHOWERS  
ACROSS PORTIONS OF SOUTHEASTERN AND EASTERN PUERTO RICO AS WELL AS  
ACROSS PORTIONS OF THE USVI DURING THE OVERNIGHT AND EARLY  
MORNING HOURS OF FRIDAY. THEN, AS THE LOW-LEVEL MOISTURE COMBINES  
WITH STRONG DAYTIME HEATING AND LOCAL EFFECTS, SCATTERED SHOWERS  
AND ISOLATED THUNDERSTORMS WILL DEVELOP AND AFFECT PORTIONS OF  
NORTHWEST PUERTO RICO AND POSSIBLY DOWNWIND OF THE USVI AND EL  
YUNQUE, AFFECTING THE SAN JUAN METRO AREA, DURING THE EARLY TO  
MID-AFTERNOON HOURS. GIVEN THAT THERE WILL BE A MID TO UPPER-LEVEL  
RIDGE NEAR THE AREA, UPPER-LEVEL DYNAMICS ARE EXPECTED TO REMAIN  
NON-EXISTENT. IN ADDITION, THE LOW-LEVEL FLOW WILL REMAIN PRETTY  
FAST FROM THE EAST-SOUTHEAST BETWEEN 15 AND 20 KNOTS. THESE  
FACTORS WILL LIMIT THE INTENSITY AS WELL AS THE DURATION OF THE  
SHOWERS, THEREFORE, SIGNIFICANT RAINFALL ACCUMULATIONS ARE NOT  
EXPECTED.  
 

 
   
AVIATION
 
MAINLY VFR CONDITIONS ARE EXPECTED DURING THE FORECAST  
PERIOD. VCSH EXPECTED ACROSS TJSJ/TISX/TIST/TNCM/TKPK. SCT  
SHRA/TSRA EXPECTED ACROSS NORTHWEST PR BETWEEN 23/16Z AND 22/23Z,  
AFFECTING THE VICINITY OF TJMZ/TJBQ. BRIEF MVFR CONDITIONS ARE  
POSSIBLE. LIGHT AND VARIABLE WINDS OVERNIGHT, INCREASING TO 10 TO  
20 KTS WITH HIGHER GUSTS FROM ESE WITH SEA BREEZE VARIATIONS  
DEVELOPING AFTER 23/13Z.  
 

 
   
MARINE
 
CHOPPY SEAS UP TO 6 FEET EXPECTED ACROSS THE ATLANTIC  
WATERS, THEREFORE, SMALL CRAFT OPERATORS SHOULD EXERCISE CAUTION.  
SEAS OF UP TO 5 FEET EXPECT ELSEWHERE. WINDS ARE EXPECTED TO RANGE  
BETWEEN 10 AND 20 KNOTS FROM THE EAST. THERE IS A MODERATE RISK  
OF RIP CURRENTS ACROSS THE NORTHERN AND SOUTHEASTERN BEACHES OF  
PUERTO RICO AND ACROSS MOST OF THE BEACHES OF VIEQUES, CULEBRA,  
AND SAINT CROIX THROUGH TONIGHT. IN ADDITION TO THESE  
AFORMENTIONED AREAS, THE MODERATE RISK OF RIP CURRENTS WILL  
EXTEND TO THE SOUTHWESTERN BEACHES OF PUERTO RICO AS WELL AS THE  
NORTHWESTERN BEACHES OF SAINT THOMAS ON FRIDAY.  
 

 
   
PREV DISCUSSION
 
/ISSUED 145 PM AST THU AUG 22 2019/  
 
SYNOPSIS...PASSING TROPICAL WAVE AND ASSOCIATE PLUME OF MOISTURE  
WILL AFFECT THE REGION THROUGH FRIDAY. RELATIVE STABLE CONDITIONS  
ARE EXPECTED ON SATURDAY, BEFORE THE NEXT TROPICAL WAVE  
APPROACHES THE REGION LATE SATURDAY NIGHT INTO SUNDAY. ALTHOUGH  
THE ENTRANCE OF RELATIVELY DRIER AND STABLE AIR MASS ACCOMPANIED  
BY SUSPENDED SAHARAN DUST WILL DOMINATE THE LOCAL AREA, LOCALLY  
INDUCED SHOWERS ARE EXPECTED EACH AFTERNOON. LACK OF UPPER LEVEL  
SUPPORT WILL LIMIT THUNDERSTORM DEVELOPMENT.  
 
SHORT TERM...TONIGHT THROUGH SATURDAY...  
 
REMNANTS FROM AFTERNOON SHOWER AND THUNDERSTORM ACTIVITY IS  
EXPECTED TO LINGER ACROSS PORTIONS OF NORTHWESTERN PUERTO RICO AND  
WATERS WEST OF PUERTO RICO THROUGH THE EVENING HOURS. DURING THE  
OVERNIGHT AND EARLY MORNING HOURS, SHOWERS AND POSSIBLE ISOLATED  
THUNDERSTORMS, ASSOCIATED TO A PASSING TROPICAL WAVE, ARE EXPECTED  
TO AFFECT THE REGIONAL WATERS AND PORTIONS OF EASTERN PUERTO RICO  
AND THE U.S. VIRGIN ISLANDS. AS THE DAY PROGRESSES, LOCALLY  
INDUCED SHOWERS ARE EXPECTED TO DEVELOP OVER THE NORTHWESTERN  
QUADRANT OF PUERTO RICO, AS WELL AS DOWNWIND FROM THE LOCAL  
ISLANDS AND SIERRA DE LUQUILLO. ALTHOUGH UPPER LEVEL SUPPORT FOR  
THUNDERSTORM DEVELOPMENT IS NOT EXPECTED, ISOLATED THUNDERSTORMS  
CANNOT BE RULED OUT IN THE AFTERNOON. LOCALIZED URBAN AND SMALL  
STREAM FLOODING POSSIBLE ACROSS THE NORTHWESTERN QUADRANT OF THE  
ISLAND.  
 
SOMEWHAT IMPROVED CONDITIONS ARE EXPECTED BETWEEN LATE FRIDAY  
NIGHT INTO SATURDAY. HOWEVER, LOCALLY INDUCED SHOWERS ARE  
POSSIBLE, PARTICULARLY DURING THE AFTERNOON HOURS. IF ANY, ABOVE-  
NORMAL TEMPERATURES AND HEAT INDEX WILL BE A THREAT DURING THIS  
PERIOD.  
 
LONG TERM...SUNDAY THROUGH WEDNESDAY...  
 
PREV DISCUSSION... /ISSUED 503 AM AST THU AUG 22 2019/  
 
SUNDAY, RESIDUAL MOISTURE ASSOCIATED WITH A TROPICAL WAVE WILL LINGER  
THROUGH THE EARLY AFTERNOON ON SUNDAY. THE MOISTURE COUPLED WITH  
DAYTIME HEATING AND LOCAL EFFECTS WILL YIELD SHOWERS AND  
THUNDERSTORMS DURING THE AFTERNOON ACROSS THE INTERIOR AND WESTERN  
AREAS OF PUERTO RICO. THERE IS A POSSIBILITY FOR URBAN AND SMALL  
STREAM FLOODING DURING THE AFTERNOON IN FLOOD PRONE AREAS. SUNDAY  
EVENING THE MOISTURE WILL ABATE AS A DRY SAHARAN AIR MASS PUSH IN  
FROM THE EAST ATLANTIC. THE DRY SAHARAN AIR IS FORECAST TO PERSIST  
THROUGH EARLY PART OF THE NEXT WEEK. THEREFORE, EXPECT HAZY SKIES  
WITH ISOLATED TO SCATTERED SHOWERS MAINLY DURING THE AFTERNOON WITH  
THE CHANCE FOR ISOLATED THUNDERSTORMS OVER WESTERN PUERTO RICO. ONCE  
AGAIN SHOWERS WILL DEVELOP DUE TO DAYTIME HEATING AND LOCAL EFFECTS.  
HOWEVER, DUE TO MODEST LOW-LEVEL MOISTURE AND LIMITED UPPER-LEVEL  
INSTABILITY AS A RESULT OF MID TO UPPER-LEVEL RIDGES SHOWERS WILL BE  
SHORT-LIVED. BY TUESDAY THE 700 MB HIGH SHIFT TO THE SOUTHWEST THIS  
SHIFT IN THE HIGH WILL ALLOW THE TROPICAL MOISTURE TO POOL INTO THE  
REGION FROM THE EAST. THE RETURN OF THE DEEP TROPICAL MOISTURE WILL  
CAUSE THE DRY SAHARAN AIR TO DIMINISH OVER THE REGION. ALSO, THE  
TROPICAL MOISTURE WILL AID IN THE DEVELOPMENT OF SHOWERS AND  
ISOLATED THUNDERSTORMS DURING THE AFTERNOON ESPECIALLY OVER AND  
SOUTH OF THE CORDILLERA CENTRAL THROUGH THE MIDDLE OF THE WEEK.  
 
AVIATION...BRIEF PERIODS OF MVFR CONDS WILL REMAIN POSSIBLE AT JBQ  
IN SHRA/TSRA THROUGH ABOUT 22/22Z. AS THE TROPICAL WAVE MOVES AWAY  
TONIGHT, CONDITIONS WILL IMPROVE WITH VCSH POSSIBLE AT THE LEEWARD  
AND USVI TERMINALS OVERNIGHT. ESE WINDS AT 10 TO 15 KNOTS WITH SOME  
SEA BREEZE VARIATIONS THROUGH 22/22Z BECOMING LIGHT AND VARIABLE  
OVERNIGHT.  
 
MARINE...CHOPPY MARINE CONDITIONS WITH SEAS UP TO 6 FEET AND  
WINDS UP TO 20 KNOTS EXPECTED ACROSS THE ATLANTIC WATERS. THUS,  
SMALL CRAFT OPERATORS SHOULD EXERCISE CAUTION ACROSS THESE AREAS.  
ELSEWHERE, TRANQUIL MARINE CONDITIONS WITH SEAS UP TO 5 FEET AND  
WINDS UP TO 15 KNOTS ARE EXPECTED TO PREVAIL. THERE IS A MODERATE  
RISK OF RIP CURRENTS FOR THE NORTHERN AND SOUTHEASTERN BEACHES OF  
PUERTO RICO, AS WELL AS MOST BEACHES OF VIEQUES, CULEBRA AND SAINT  
CROIX.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SJU 78 91 78 90 / 40 10 50 50  
STT 80 91 80 88 / 40 30 40 40  
 

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

 

 
 
SHORT TERM...GL  
LONG TERM....WS  
 
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