942  
FXCA62 TJSJ 290753  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
353 AM AST WED MAR 29 2017  
   
SYNOPSIS
 
A SURFACE HIGH ACROSS THE SOUTHWEST ATLANTIC WILL  
PUSH THE SURFACE LOW TO THE NORTHEAST OF THE REGION FURTHER  
NORTHEAST WELL AWAY FROM THE LOCAL ISLANDS. AS THIS HAPPENS, THE  
LOCAL WINDS WILL SHIFT TO THE NORTH NORTHEAST TODAY. LINGERING  
MOISTURE ACROSS THE REGION WILL COMBINE WITH LOCAL EFFECTS TO  
INDUCE THE DEVELOPMENT OF SHOWERS AND POSSIBLE THUNDERSTORMS ALONG  
AND SOUTH OF CORDILLERA CENTRAL TODAY. WINDS ARE EXPECTED TO  
BECOME MORE EASTERLY BY THE WEEKEND AS THE SURFACE HIGH DRIFT  
EASTWARD WHILE WEAKENING. NORTH SWELL IS EXPECTED TO AFFECT THE  
LOCAL WATERS LATE WEDNESDAY AND THURSDAY.  
 

 
   
SHORT TERM...TODAY THROUGH FRIDAY
 
 
PARTLY CLOUDY SKIES PREVAILED ACROSS THE LOCAL ISLANDS OVERNIGHT.  
SOME LIGHT PASSING SHOWERS WERE SEEN ACROSS THE CARIBBEAN COASTAL  
WATERS. LOCAL AREA REMAINS UNDER THE INFLUENCE OF A SURFACE LOW  
PRESSURE SYSTEM WHICH WAS LOCATED SEVERAL HUNDRED MILES NORTHEAST OF  
THE AREA. TRAILING MOISTURE ASSOCIATED WITH THIS FEATURE WILL  
CONTINUE TO AID IN THE DEVELOPMENT OF SHOWERS AND POSSIBLE  
THUNDERSTORMS MAINLY OVER THE CORDILLERA CENTRAL OF PUERTO RICO. THE  
DIFFERENCE TODAY IT IS THAT THE WIND HAS SHIFTED NORTHERLY. AS A  
RESULT,SHOWER ACTIVITY WILL BE FOCUS MAINLY OVER THE SOUTHERN SLOPES  
OF PUERTO RICO.  
 
AS THE AFORMENTIONED AREA OF LOW PRESSURE CONTINUE TO MOVE AWAY FROM  
THE AREA, A DRIER AIRMASS IS EXPECTED TO ENCOMPASS THE REGION  
THURSDAY AND FRIDAY AS A HIGH PRESSURE SYSTEM BUILDS ACROSS THE  
WESTERN ATLANTIC.  
   
LONG TERM...SATURDAY THROUGH WEDNESDAY
 
 
A WEAK SURFACE HIGH PRESSURE IS EXPECTED TO DEVELOP ACROSS THE  
CENTRAL ATLANTIC EARLY IN THE WEEKEND TO MAINTAIN AN EASTERLY TRADE  
WIND FLOW ACROSS THE LOCAL ISLANDS SATURDAY AND SUNDAY. AT THE SAME  
TIME A SURFACE LOW EMERGING ACROSS THE NORTHEASTERN UNITED STATES  
SEABOARD WILL PUSH THE SURFACE HIGH EASTWARD WHILE WEAKENING. AS  
THIS HAPPENS PATCHES OF MOISTURE ASSOCIATED WITH A FRONTAL  
REMNANTS WILL COMBINE WITH LOCAL EFFECTS BOTH DAYS TO PRODUCE AN  
INCREASE IN CLOUDINESS AND SHOWER ACTIVITY ACROSS PUERTO RICO AND  
THE U.S. VIRGIN ISLANDS DURING THE WEEKEND, BUT AT THIS TIME NOT  
WIDESPREAD OR SIGNIFICANT PRECIPITATION IS EXPECTED DURING THIS  
PERIOD.  
 
AS THE AFOREMENTIONED SURFACE LOW AND ASSOCIATED FRONTAL BOUNDARY  
MOVES NORTHEASTWARD TOWARD THE NORTH CENTRAL ATLANTIC, ANOTHER  
STRONGER SURFACE HIGH IS EXPECTED TO DEVELOP AND DRIFT ACROSS THE  
WESTERN ATLANTIC. THIS FEATURE WILL BRING AN EAST NORTHEAST TRADE  
WIND FLOW ACROSS THE FORECAST AREA LATE MONDAY THROUGH AT LEAST  
WEDNESDAY. AN UPPER LEVEL RIDGE IS EXPECTED TO BUILD AND  
STRENGTHENING OVER THE NORTHEAST CARIBBEAN DURING THE WEEKEND AND  
IS EXPECTED TO PERSIST OVER THE REGION THROUGH AT LEAST WEDNESDAY.  
THIS FEATURE WILL INHIBIT THE DEVELOPMENT OF WIDESPREAD OR DEEP  
CONVECTION ACROSS THE LOCAL ISLANDS DURING THE FORECAST PERIOD,  
BUT MOISTURE EMBEDDED IN THE TRADES WILL CONTINUE TO COMBINE WITH  
LOCAL EFFECTS TO PRODUCE SOME SHOWER ACTIVITY ACROSS WESTERN AND  
INTERIOR PUERTO RICO EACH DAY.  
 

 
   
AVIATION
 
MAINLY VFR CONDITIONS ARE EXPECTED TO PREVAIL ACROSS ALL  
TAF SITES THROUGH AT LEAST 29/16Z. PERIODS OF MVFR CONDITIONS CAN BE  
EXPECTED ACROSS TJPS AND TJMZ BETWEEN 29/16Z THROUGH 29/22Z IN SHRA.  
LOW LEVEL WINDS WILL BE MAINLY NORTH AND NORTHWEST AT 10 KTS OR  
LESS.  
 

 
   
MARINE
 
SEAS OF 3 TO 5 FEET WILL CONTINUE TO PREVAIL ACROSS  
THE ATLANTIC WATERS, WITH SEAS 2 TO 4 FEET ACROSS THE CARIBBEAN  
WATERS. A MODERATE RISK OF RIP CURRENT WILL CONTINUE ACROSS THE  
ATLANTIC SHORELINE OF PUERTO RICO TODAY AND TONIGHT. A NORTHERLY  
SWELL WILL ARRIVE ACROSS THE LOCAL WATERS LATE WEDNESDAY INTO  
THURSDAY WITH SEAS INCREASING UP TO 6 FEET.  
 

 
   
PRELIMINARY POINT TEMPS/POPS
 
 
SJU 84 75 84 74 / 20 10 10 10  
STT 84 74 85 73 / 40 20 20 20  
 

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

 
 

 
 
SHORT TERM...FC  
LONG TERM....JF  
 
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