621  
FXCA62 TJSJ 230910  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
510 AM AST SUN JUL 23 2017  
   
SYNOPSIS
 
LINGERING MOISTURE ASSOCIATED WITH A DEPARTING  
TROPICAL WAVE WILL PREVAIL EARLY THIS MORNING FOLLOWED BY A  
DRIER AIR MASS MOVING INTO THE FORECAST AREA. THE PROXIMITY  
OF AN UPPER LEVEL TROUGH WILL ASSURE SHOWER AND THUNDER  
DEVELOPMENT EACH AFTERNOON TUESDAY THROUGH THE UPCOMING  
WEEKEND.  
 

 
   
SHORT TERM...SUNDAY THROUGH TUESDAY
 
 
ALTHOUGH A TROPICAL WAVE CONTINUES TO MOVE FARTHER AWAY AND  
A DRIER MASS WILL ENCOMPASS THE FORECAST AREA; THE CHANCE FOR  
SHOWER AND THUNDERSTORM DEVELOPMENT REMAINS POSSIBLE ACROSS THE  
LOCAL ISLANDS TODAY.  
 
AS A DRIER MASS ENCOMPASS THE LOCAL ISLANDS, MOSTLY FAIR WEATHER  
CONDITIONS AS WELL AS AN INCREASE IN SAHARAN DUST PARTICULATE ARE  
EXPECTED ACROSS THE FORECAST AREA. HOWEVER, LINGERING LOW-LEVEL  
MOISTURE COMBINED WITH THE LOCAL AND DIURNAL EFFECTS WILL RESULT  
IN THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS ACROSS THE INTERIOR  
AND WESTERN PR, AS WELL AS OVER THE SAN JUAN METROPOLITAN AREA  
WITHIN THE SAN JUAN STREAMER IN THE AFTERNOON. LIMITED SHOWER  
ACTIVITY EXPECTED MONDAY AND EARLY TUESDAY.  
   
LONG TERM...WEDNESDAY THROUGH SUNDAY
 
 
WEAK RIDGE PATTERN ALOFT IS EXPECTED TO ERODE BY THURSDAY AS A  
MID TO UPPER LEVEL TROUGH WHICH IS NOW LOCATED ACROSS THE CENTRAL  
ATLANTIC SHIFTS WESTWARD. THE AFOREMENTIONED THROUGH IS EXPECTED  
TO PREVAIL NORTH OF THE LOCAL ISLANDS THROUGH THE UPCOMING WEEKEND.  
THE PROXIMITY OF THIS FEATURE COMBINED WITH PRECIPITABLE WATER  
VALUES NEAR OR SLIGHTLY ABOVE THE NORMAL RANGE WILL ASSURE AFTERNOON  
SHOWERS AND THUNDERSTORMS ACROSS THE INTERIOR AND WEST SECTIONS  
OF PUERTO RICO EACH DAY. A BROAD SURFACE HIGH PRESSURE ACROSS THE  
CENTRAL ATLANTIC WILL YIELD EAST SOUTHEAST WINDS THROUGH THE  
FORECAST PERIOD TO RESULT IN ABOVE NORMAL TEMPERATURES PARTICULARLY  
ACROSS THE NORTHERN SLOPES OF PUERTO RICO.  
 

 
   
AVIATION
 
MAINLY VFR CONDITIONS EXPECTED TO PREVAIL ACROSS ALL  
TERMINALS. HOWEVER, BRIEF RA/VCSH PERIODS POSSIBLE AT TIMES  
THROUGH 12Z ACROSS THE USVI/EASTERN PR TERMINALS. SHRA/TSRA  
POSSIBLE BETWEEN 16Z-22Z ACROSS THE NORTHWEST SECTIONS OF PR,  
IMPACTING MAINLY TJBQ/TJMZ. LOW LEVEL WINDS EXPECTED TO PREVAIL  
ESE AT 8-15 KTS WITH SEA BREEZE VARIATIONS AFTER 14Z.  
 

 
   
MARINE
 
TRANQUIL MARINE CONDITIONS ARE EXPECTED TO PREVAIL  
DURING THE NEXT SEVERAL DAYS WITH SEAS 3 TO 5 FEET AND EASTERLY  
WINDS 15 TO 20 KNOTS.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SJU 89 81 89 81 / 30 10 10 30  
STT 90 79 90 79 / 30 10 20 40  
 

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

 
 

 
 
SHORT TERM...ICP  
LONG TERM....OM  
AVIATION.....DS  
 
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