527  
FXCA62 TJSJ 240849  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
449 AM AST THU MAY 24 2018  
   
SYNOPSIS
 
A SHORT WAVE TROUGH ALOFT IS FORECAST TO SWING NORTH OF THE  
ISLANDS AS A TUTT LOW MOVES NORTHEASTWARD FROM THE LEEWARD  
ISLANDS THE NEXT FEW DAYS. THE ISLANDS WILL BE WEDGE BY A RIDGE  
TO THE NORTHWEST AND A TUTT LOW TO THE NORTHEAST THROUGH THE  
UPCOMING WEEKEND. TROPICAL WAVE WILL APPROACH THE LESSER ISLANDS  
BETWEEN SATURDAY NIGHT INTO SUNDAY MORNING.  
 

 
   
SHORT TERM...TODAY THROUGH SATURDAY
 
 
NOT MUCH CHANGE TO THE LOCAL WEATHER PATTERN IS EXPECTED FOR TODAY  
ACROSS THE FORECAST AREA. PARTLY TO VARIABLY CLOUDY SKIES WITH BRIEF  
PASSING SHOWER ACTIVITY ARE EXPECTED ACROSS EASTERN PORTIONS OF  
PUERTO RICO AND THE USVI DURING THE MORNING HOURS. DURING THE  
AFTERNOON, HEAVY SHOWERS AND POSSIBLY A FEW ISOLATED THUNDERSTORMS  
ARE EXPECTED TO DEVELOP ACROSS THE NORTHWEST QUADRANT OF PUERTO  
RICO. ADDITIONAL SHOWER DEVELOPMENT IS EXPECTED ACROSS THE SAN JUAN  
METRO AREA DOWNWIND FROM EL YUNQUE AS WELL AS SOME POSSIBLE  
STREAMERS DEVELOPING DOWNWIND FROM THE USVI. THE RAINFALL EXPECTED  
ACROSS THE NORTHWEST QUADRANT OF PUERTO RICO AS WELL AS ACROSS THE  
SAN JUAN METRO AREA COULD RESULT IN PONDING OF WATER ON ROADWAYS AND  
IN POOR DRAINAGE AREAS AS WELL AS SOME LOCALIZED URBAN AND SMALL  
STREAM FLOODING.  
 
MODEL GUIDANCE CONTINUES TO INDICATE AN INCREASE IN LOW-LEVEL  
MOISTURE VIA A SOUTHEASTERLY WIND FLOW FOR FRIDAY AND SATURDAY.  
THEREFORE, CONTINUE TO EXPECT PASSING TRADE WIND SHOWERS AFFECTING  
EASTERN PORTIONS OF PUERTO RICO AND USVI DURING THE MORNING HOURS  
FOLLOWED BY HEAVY SHOWERS DEVELOPING ACROSS THE NORTHWEST QUADRANT  
OF PUERTO RICO AS WELL AS ACROSS PORTIONS OF THE SAN JUAN METRO AREA  
DOWNWIND FROM EL YUNQUE DURING THE AFTERNOON HOURS. GIVEN THE RECENT  
RAINFALL ACTIVITY, THE POTENTIAL EXISTS FOR URBAN AND SMALL STREAM  
FLOODING WHERE THE HEAVIEST RAINFALL OCCURS.  
   
LONG TERM...SUNDAY THROUGH FRIDAY
 
 
AN INCREASE IN LOW LEVEL MOISTURE IS EXPECTED BY EARLY NEXT WEEK  
AS A TROPICAL WAVE COMBINE WITH AN UPPER LEVEL TROUGH AND PLENTY  
OF LOW LEVEL MOISTURE AT THE SURFACE. AS A RESULT, SCATTERED TO  
NUMEROUS SHOWERS WITH ISOLATED THUNDERSTORMS ARE EXPECTED TO  
AFFECT THE LOCAL AREA SUNDAY INTO MONDAY. BEST ACTIVITY IS  
EXPECTED TO DEVELOP ACROSS THE CORDILLERA CENTRAL OF PUERTO RICO.  
A DRIER AIR MASS IS EXPECTED TO ENCOMPASS THE REGION TUESDAY AND  
WEDNESDAY, FOLLOWED BY ANOTHER TROPICAL WAVE WHICH IS FORECAST BY  
SJU-GFS MODEL TO REACH THE NORTHEAST CARIBBEAN BY THURSDAY NEXT  
WEEK.  
 

 
   
AVIATION
 
MAINLY VFR CONDS EXPECTED ACROSS ALL TERMINALS THROUGH  
24/16Z. A FEW BRIEF PASSING SHRA COULD AFFECT THE USVI AND TJSJ  
TERMINALS DURING THE MORNING HOURS. +SHRA AND ISOLATED TS  
DEVELOPMENT EXPECTED ACROSS WESTERN AND NORTHWESTERN SECTIONS OF PR  
AFTER 24/16Z. THEREFORE, MVFR CONDITIONS ARE EXPECTED ACROSS TJBQ  
AND TJMZ TERMINALS. VCSH POSSIBLE ACROSS TJSJ BETWEEN 24/16-20Z.  
WINDS WILL BE FROM THE E-SE BETWEEN 15-20 KTS WITH SEA BREEZE  
VARIATIONS AND OCCASIONAL GUSTS THROUGH 24/22Z. WINDS EXPECTED TO  
DIMINISH BELOW 10KTS AFTER 24/23Z.  
 

 
   
MARINE
 
SEAS BETWEEN 4 TO 6 FEET AND WINDS UP TO 20 KNOTS ARE  
EXPECTED ACROSS THE LOCAL WATERS. SMALL CRAFT OPERATORS ARE URGE  
TO EXERCISE CAUTION ACROSS MOST WATERS.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SJU 87 77 87 77 / 40 40 40 30  
STT 87 77 87 77 / 30 30 30 30  
 

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

 
 

 
 
SHORT TERM...GL  
LONG TERM....FC  
 
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