449  
FXCA62 TJSJ 220026  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
826 PM AST TUE NOV 21 2017  
   
UPDATE
 
PARTLY CLOUDY SKIES PREVAILED ACROSS PUERTO RICO THIS  
EVENING. DOPPLER WEATHER RADAR AND SATELLITES IMAGES DEPICTED  
ONLY FEW PASSING SHOWERS ACROSS THE LOCAL WATERS. HOWEVER, NOT  
SIGNIFICANT PRECIPITATION WAS OBSERVED OVER LAND AREAS. ALTHOUGH  
A MID TO UPPER LEVEL RIDGE WILL CONTINUE TO BUILD ACROSS THE  
FORECAST AREA TONIGHT AND HOLD THROUGH MUCH OF THE WEEK, EAST  
SOUTHEASTERLY WINDS WILL CONTINUE TO BRING PATCHES OF LOW LEVEL  
MOISTURE AT TIMES. THEREFORE, EXPECT A FAIR AND GENERALLY STABLE  
WEATHER PATTERN TONIGHT THROUGH AT LEAST WEDNESDAY WITH LIGHT  
PASSING SHOWERS ACROSS EASTERN PR IN THE MORNING FOLLOWED BY  
LIMITED SHOWER ACTIVITY ACROSS WESTERN PUERTO RICO IN THE  
AFTERNOON. THE CHANCE FOR SHOWER ACTIVITY WILL INCREASE WEDNESDAY  
NIGHT INTO THURSDAY AS LOW LEVEL MOISTURE INCREASES ACROSS THE  
EASTERN CARIBBEAN.  
 

 
   
AVIATION
 
MOSTLY VFR CONDITIONS EXPECTED ACROSS THE LOCAL FLYING  
AREA DURING THE PERIOD. FEW -SHRA EN ROUTE BTW ISLANDS WITH FEW-  
SCT CLD LYRS NR FL030...FL050 OVERNIGHT TIL 22/14Z. L/LVL WNDS FROM  
SE 10-15 KTS, BLO FL100...BCMG SW-W THEN INCR W/HT ABV. SFC WND  
LGT/VRB...BCMG E-SE 10-15 KTS WITH SEA BREEZE VARIATIONS ALONG  
THE COASTAL AREAS AFT 22/14Z. NO SIG WX IMPACT ACROSS THE REGION  
ATTM.  
 

 
   
MARINE
 
SEAS WILL CONTINUE BETWEEN 3-5 FEET ACROSS THE OFFSHORE  
WATERS AND BETWEEN 2-4 FEET ACROSS THE COASTAL WATERS OVERNIGHT.  
SEAS INCREASE UP TO 7 FEET ACROSS THE OFFSHORE ATLANTIC WATERS  
BETWEEN WEDNESDAY NIGHT AND THURSDAY. A SMALL CRAFT ADVISORY WILL  
BE IN EFFECT THROUGH THIS PERIOD. A MODERATE RISK OF RIP CURRENTS  
WILL CONTINUE FOR THE NEXT SEVERAL DAYS ACROSS THE ATLANTIC  
BEACHES OF THE ISLANDS.  
 

 
   
PREV DISCUSSION
 
/ISSUED 505 PM AST TUE NOV 21 2017/  
 
SYNOPSIS...A MID TO UPPER LEVEL RIDGE WILL CONTINUE TO DOMINATE  
THE LOCAL WEATHER PATTERN DURING THE NEXT SEVERAL DAYS. DRIER AIR  
WILL CONTINUE THROUGH WEDNESDAY. MOISTURE INCREASES ONCE AGAIN ON  
THURSDAY AND FRIDAY AS AN INDUCED SURFACE TROF MOVES FROM THE  
EAST. DRIER CONDITIONS RETURN DURING THE WEEKEND.  
 
SHORT TERM...TODAY THROUGH THURSDAY...  
 
LITTLE TO NONE RAIN WAS OBSERVED TODAY OVER LAND AREAS. MOSTLY  
SUNNY SKIES PREVAILED ACROSS ALL ISLANDS. FAIR WEATHER CONDITIONS  
WILL CONTINUE THROUGH WEDNESDAY. A FEW ISOLATED SHOWERS CANT BE  
RULED OUT ACROSS WESTERN PR DURING THE AFTERNOON HOURS. ON  
THURSDAY, AS A WEAK PERTURBATION/INDUCED TROF MOVES FROM THE  
EAST...MOISTURE WILL INCREASE AND A BETTER CHANCE FOR SHOWER WITH  
POSSIBLE ISOLATED THUNDERSTORM DEVELOPMENT IS EXPECTED ALONG THE  
THE CORDILLERA CENTRAL DURING THURSDAY AFTERNOON. TEMPERATURES  
WILL CONTINUE BETWEEN THE HIGH 80S TO LOW 90S ACROSS THE LOWER  
ELEVATIONS EACH DAY.  
 
LONG TERM....FROM PREVIOUS DISCUSSION....FRIDAY THROUGH  
WEDNESDAY...  
 
HIGH PRESSURE THAT FORMS JUST NORTH OF THE MONA CHANNEL WEDNESDAY  
NIGHT WILL BRING IN MOISTURE ON THURSDAY FROM THE NORTHEAST THAT  
WILL LINGER UNTIL EARLY SATURDAY MORNING. THIS AND THE EASTERLY  
WAVE THAT WILL MOVE THROUGH ON FRIDAY WILL CONTINUE THE GOOD  
CHANCES FOR BOTH NIGHT AND EARLY MORNING SHOWERS IN EASTERN PUERTO  
RICO AND THE U.S. VIRGIN ISLANDS AND SHOWERS AND ISOLATED  
THUNDERSTORMS IN WESTERN PUERTO RICO IN THE AFTERNOON. A BREAK IN  
THE MOISTURE WILL OCCUR OVER THE WEEKEND. AS A COLD FRONT SWEEPS  
DOWN THROUGH THE LAST OF THE BAHAMA ISLANDS ON MONDAY A NEW SURGE  
OF TROPICAL MOISTURE INVADES THE AREA FROM THE CARIBBEAN SEA TO  
THE SOUTH. LOWER LEVELS WILL THEN SEE WET AND DRY PERIODS DURING  
THE FIRST PART OF NEXT WEEK AND THE FRONT WILL LIFT TO THE NORTH  
MID WEEK NEXT WEEK BEFORE REACHING THE AREA.  
 
THE RIDGE OF HIGH PRESSURE AT UPPER LEVELS WILL CONTINUE JUST  
EAST OF THE AREA AND KEEP CONVECTION LIMITED. THE DEEP LONG WAVE  
TROUGH INVADING THE WESTERN ATLANTIC ON SUNDAY WILL WEAKEN IN THE  
PROCESS OF FLATTENING THAT RIDGE IN ITS PASSAGE THROUGH THE AREA  
ON WEDNESDAY OF NEXT WEEK. ALTHOUGH GOOD MOISTURE WILL BE  
AVAILABLE DURING THE WEEK NEXT WEEK IT WILL NOT BE AS STRONG AS  
HAS OCCURRED IN THE LAST FEW DAYS.  
 
AVIATION...VFR CONDS ACROSS THE FLYING AREA AND AT ALL TERMINALS  
DURG THE PRD. FEW SHRA EN ROUTE BTW ISLANDS WITH FEW-SCT CLD LYRS NR  
FL030...FL050 OVERNIGHT TIL 22/14Z. L/LVL WNDS FM SE 10-15 KTS,BLO  
FL100...BCMG SW-W THEN INCR W/HT ABV. SFC WND LGT/VRB...BCMG E-SE 10-  
15 KTS WITH SEA BREEZE VARIATIONS ALONG THE COASTAL AREAS AFT  
22/14Z. NO SIG WX IMPACT ACROSS THE REGION ATTM.  
 
MARINE...SEAS WILL CONTINUE BETWEEN 3-5 FEET ACROSS THE OFFSHORE  
WATERS AND BETWEEN 2-4 FEET ACROSS THE COASTAL WATERS THROUGH  
WEDNESDAY. SEAS INCREASE UP TO 7 FEET ACROSS THE OFFSHORE ATLANTIC  
WATERS BETWEEN WEDNESDAY NIGHT AND THURSDAY. A SMALL CRAFT  
ADVISORY WILL BE IN EFFECT THROUGH THIS PERIOD. A MODERATE RISK OF  
RIP CURRENTS WILL CONTINUE FOR THE NEXT SEVERAL DAYS ACROSS THE  
ATLANTIC BEACHES OF THE ISLANDS.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SJU 75 88 76 88 / 20 20 30 50  
STT 76 87 77 85 / 20 30 50 50  
 

 
   
SJU WATCHES/WARNINGS/ADVISORIES
 
 
PR...FLASH FLOOD WATCH THROUGH WEDNESDAY AFTERNOON FOR NORTHWEST-  
WESTERN INTERIOR.  
 
VI...NONE.  
AM...SMALL CRAFT ADVISORY FROM 8 PM WEDNESDAY TO 2 PM AST THURSDAY  
FOR ATLANTIC WATERS OF PUERTO RICO AND USVI FROM 10 NM TO  
19.5N.  
 

 
 

 
 
SHORT TERM...JF  
LONG TERM....DS  
 
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