815  
FXCA62 TJSJ 122043  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
443 PM AST WED AUG 12 2020  
   
SYNOPSIS
 
A TROPICAL WAVE CURRENTLY OVER THE AREA WILL MOVE  
AWAY TONIGHT, WITH MUCH DRIER AIR EXPECTED TO MOVE IN WITH FAIR  
WEATHER CONDITIONS EXPECTED. THIS RELATIVELY DRY AIR MASS WILL  
PREVAIL ACROSS THE AREA THROUGH THE END OF THE WORK WEEK,  
THEREFORE, SHOWER ACTIVITY WILL BE LIMITED. TROPICAL DEPRESSION  
ELEVEN, FORECAST TO BECOME A TROPICAL STORM LATER TONIGHT, IS  
STILL FORECAST TO PASS NORTH OF THE AREA DURING THE WEEKEND WITH  
NO DIRECT IMPACTS EXPECTED AT THIS TIME.  
 

 
   
SHORT TERM...TONIGHT THROUGH FRIDAY
 
 
THE SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A TROPICAL  
WAVE WILL CONTINUE TO LINGER ACROSS PORTIONS OF WESTERN PUERTO  
RICO THROUGH THE EARLY EVENING HOURS BEFORE DISSIPATING COMPLETELY.  
AS THE TROPICAL WAVE EXITS THE AREA TONIGHT, A MUCH DRIER AIR  
MASS WILL MOVE IN. THEREFORE, FAIR WEATHER CONDITIONS ARE  
EXPECTED. THIS RELATIVELY DRY AIR MASS IS EXPECTED TO PREVAIL  
THROUGH THE END OF THE WORK WEEK, RESULTING IN LIMITED SHOWER  
ACTIVITY. HOWEVER, PATCHES OF LOW-LEVEL MOISTURE WILL MOVE OVER  
THE AREA FROM TIME TO TIME, WHICH COULD CAUSE SOME PASSING  
SHOWERS TO DEVELOP ACROSS THE REGIONAL WATERS AND AFFECT PORTIONS  
OF EASTERN PUERTO RICO AND THE USVI DURING THE OVERNIGHT AND  
MORNING HOURS FOLLOWED BY THE DEVELOPMENT OF SOME AFTERNOON  
CONVECTION ACROSS WESTERN PUERTO RICO.  
 

 
   
PREV DISCUSSION
 
/ISSUED 429 AM AST WED AUG 12 2020/  
   
LONG TERM...SATURDAY THROUGH THURSDAY
 
 
THE FORECAST FOR SATURDAY, AND, INDEED, THE REST OF THE WEEKEND  
AND INTO MONDAY, IS QUITE DEPENDENT ON THE DEVELOPMENT AND  
TRAJECTORY OF TROPICAL DEPRESSION ELEVEN. SHOULD THE SYSTEM  
STRENGTHEN, AS IS PRESENTLY EXPECTED, IT WOULD BE LIKELY TO PULL  
NORTHWARD, AWAY FROM ANOTHER TROPICAL WAVE, AS IT NEARS THE  
CARIBBEAN. IN THIS SCENARIO, A DRY SLOT FORMS BETWEEN THE TROPICAL  
CYCLONE AND THE WAVE. THAT BEING SAID, THERE DOES REMAIN SOME  
UNCERTAINTY, AS WE ARE STILL SEVERAL DAYS OUT. A SHIFT IN THE  
STRENGTH OR TRAJECTORY WOULD SHIFT THE TIMING AND LOCATION OF ANY  
POSSIBLE DRY SLOT. A LESS LIKELY SCENARIO INVOLVES THE SYSTEM NOT  
STRENGTHENING, OR BEING SHORT-LIVED. THIS HAS THE POTENTIAL TO  
LEAD TO MORE MOISTURE BEING BROUGHT THROUGH THE AREA. WHILE THIS  
CURRENTLY DOES NOT LOOK LIKELY, IT CANNOT BE FULLY RULED OUT.  
EITHER WAY, IT DOES LOOK TO BE A FAIRLY RAINY WEEKEND,  
INCREASINGLY SO AS WE MOVE INTO SUNDAY. WIDESPREAD SHOWERS ARE  
LIKELY BY SUNDAY, WITH ISOLATED TO LOCALLY SCATTERED  
THUNDERSTORMS. CONDITIONS ALOFT ARE EXPECTED TO BE MORE FAVORABLE  
FOR CONVECTIVE ACTIVITY, BUT NOT VERY FAVORABLE. THIS WILL STILL  
HELP CONTRIBUTE TO THE AFTERNOON SHOWERS AND THUNDERSTORMS,  
THOUGH.  
 
MOISTURE WILL REMAIN IN THE AREA FOR MONDAY, WHEN THERE WILL LIKELY  
BE A CONTINUATION OF SUNDAY, THOUGH SLIGHTLY WEAKER IN TERMS OF  
ACTIVITY. DYNAMIC FORCING ALOFT REMAINS RELATIVELY WEAK, AND ITS  
INFLUENCE WILL WANE SOMEWHAT. DECREASING MOISTURE IS EXPECTED DURING  
THE EVENING AND INTO THE NIGHT. AND BY TUESDAY, CONDITIONS ALOFT  
WILL BECOME DECREASINGLY FAVORABLE FOR CONVECTION, WITH DRYING  
FORECAST FOR THE MID-LEVELS. A LARGE, BUT WEAK, DEVELOPING  
DISTURBANCE WILL HELP BRING ADDITIONAL MOISTURE INTO THE AREA ON  
TUESDAY INTO WEDNESDAY; MOISTURE LEVELS WILL BE NEAR-NORMAL LEVELS,  
CLIMATOLOGICALLY SPEAKING. A TYPICAL PATTERN OF AFTERNOON SHOWERS IN  
THE WEST AND PASSING SHOWERS OVERNIGHT AND INTO THE MORNING IN THE  
EAST WILL PREVAIL THROUGH MIDWEEK. FURTHER DRYING IS EXPECTED  
WEDNESDAY NIGHT INTO THURSDAY, WHICH WILL ACT TO INHIBIT SOME OF THE  
TYPICAL SHOWER ACTIVITY ACROSS THE LOCAL ISLANDS.  
 

 
   
AVIATION
 
 
TROPICAL WAVE MOVING ACROSS THE REGION WILL CONTINUE TO  
BRING SHRA/TSRA TO THE LOCAL FLYING AREA AT LEAST TIL 12/23Z. THIS  
WILL CAUSE VCSH/VCTS IN AND AROUND THE ISLANDS AS WELL AS OVR THE  
LOCAL FLYING AREA. SCT-BKN LYRS NR FL025...FL050...FL100 TIL 13/00Z.  
BRIEF MVFR PSBL AT TJSJ/TJBQ/TJMZ AND EN ROUTE BETWEEN ISLANDS WITH  
SHRA/ISOLD TSRA. SFC WNDS FM E-SE 10-15 KTS WITH OCNL HIR GUST WITH  
SHRA/ISOLD TSRA. WNDS BCMG FM ESE 10 KTS OR LESS AFT 12/23Z.  
 

 
   
MARINE
 
MODERATE TO FRESH EASTERLY WINDS BETWEEN 15 AND 20 KNOTS  
WILL CONTINUE TO RESULT IN SEAS OF BETWEEN 3 AND 6 FEET ACROSS THE  
REGIONAL WATERS, WITH THE HIGHEST SEAS EXPECTED ACROSS THE  
OFFSHORE WATERS. TROPICAL DEPRESSION ELEVEN, CURRENTLY LOCATED  
OVER THE CENTRAL TROPICAL ATLANTIC, IS FORECAST TO MOVE NORTH OF  
THE LOCAL AREA DURING THE UPCOMING WEEKEND. THIS COULD GENERATE  
SOME HAZARDOUS SEAS, MAINLY ACROSS THE OFFSHORE ATLANTIC WATERS. A  
MODERATE RISK OF RIP CURRENTS IS EXPECTED FOR SEVERAL OF THE  
LOCAL BEACHES OF THE ISLANDS, EXCEPT ACROSS THE WESTERN COAST OF  
PUERTO RICO, THROUGH THURSDAY.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SJU 80 90 80 89 / 40 20 20 40  
STT 81 90 80 91 / 40 20 20 40  
 

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

 
 

 
 
SHORT TERM...DSR  
LONG TERM....GL  
PUBLIC DESK...LIS  
 
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