180  
FXCA62 TJSJ 040824  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
424 AM AST FRI JUL 4 2025  
   
KEY MESSAGES
 
 
* THE INCREASE IN MOISTURE FROM A TROPICAL WAVE WILL ENHANCE PEAK  
HEAT INDICES AROUND THE COASTAL AREAS, RESULTING IN AN  
ELEVATED HEAT THREAT FOR VULNERABLE COMMUNITIES SUCH AS ADULTS  
AGED 65 AND OLDER AND CHILDREN. STAY HYDRATED THROUGHOUT THE  
DAY.  
 
* A TROPICAL WAVE WILL INCREASE THE POTENTIAL FOR SHOWERS  
ACROSS NORTHWESTERN PUERTO RICO.  
 
* A PULSE OF SAHARAN DUST PARTICLES WILL MOVE INTO THE AREA,  
RESULTING IN HAZY SKIES AT LEAST UNTIL MONDAY.  
 
* THERE IS A LOW RISK OF RIP CURRENT FOR ALL BEACHES ACROSS THE  
ISLANDS TODAY 4TH OF JULY.  
 

 
   
SHORT TERM...TODAY THROUGH SUNDAY
 
 
THE NIGHT WAS TRANQUIL WITH VERY LITTLE RAIN OBSERVED OVER LAND OR  
NEAR THE LOCAL WATERS. THERE ARE SOME THUNDERSTORMS WELL TO THE  
NORTH ASSOCIATED WITH A TROUGH, AND ANOTHER CLUSTER OF STORMS OVER  
THE CARIBBEAN SEA.  
 
A SURFACE HIGH PRESSURE WILL MAINTAIN A PRONOUNCED EAST-SOUTHEAST  
WIND FLOW TODAY. THIS WIND FLOW WILL CAUSE TEMPERATURES TO SOAR ONCE  
AGAIN, WITH HIGHS IN THE UPPER 80S AND LOW 90S, AND ELEVATED HEAT  
INDICES FOR MOST COASTAL AND URBAN AREAS. THIS LEVEL OF HEAT WILL BE  
PARTICULARLY DANGEROUS FOR THOSE MOST SENSITIVE TO HEAT OR WITHOUT  
ADEQUATE HYDRATION OR COOLING. MEANWHILE, A TROPICAL WAVE WILL MOVE  
SOUTH OF THE REGION, INCREASING MOISTURE A BIT. THIS WAVE WILL BRING  
SOME PASSING SHOWERS OVER EASTERN PUERTO RICO AND THE VIRGIN  
ISLANDS, BUT THE STRONGEST ACTIVITY IS ANTICIPATED TO DEVELOP IN THE  
INTERIOR AND NORTHWEST. THE COMBINATION OF STRONG DIURNAL HEATING  
AND THE AVAILABLE MOISTURE HAVE THE POTENTIAL TO TRIGGER STRONG  
THUNDERSTORMS ACROSS THE INTERIOR AND NORTHWEST, WITH A LOCALIZED,  
BUT ELEVATED RISK OF URBAN AND SMALL STREAM FLOODING. FREQUENT  
LIGHTNING CAN BE ANTICIPATED WITH THESE STORMS AS WELL.  
 
AS THE WAVE DEPARTS, A DENSE SAHARAN AIR LAYER FOLLOWS, WITH HIGH  
CONCENTRATIONS OF PARTICULATE ANTICIPATED. THE AIR MASS WILL BEGIN  
TO REACH THE VIRGIN ISLANDS THIS MORNING, AND THEN ADVANCING INTO  
PUERTO RICO IN THE AFTERNOON. HAZY SKIES WILL PREVAIL THROUGH THE  
ENTIRE WEEKEND, SO ANYONE SENSITIVE SHOULD TAKE THE NECESSARY  
PRECAUTIONS. IT WILL BE HOT TOO, AND IT IS VERY LIKELY THAT THE  
CRITERIA FOR HEAT ADVISORIES WILL BE MET IN PUERTO RICO EACH DAY. IN  
THE VIRGIN ISLANDS, VIEQUES AND CULEBRA, THE RISK OF HEAT WILL BE  
LIMITED, SO EVERYONE IS ENCOURAGE TO STAY HYDRATED, SEEK SHADED  
AREAS, AND TAKE PLENTY OF BREAKS IF YOU NEED TO SPEND LONG PERIOD OF  
TIMES OUTSIDE. EVEN WITH THE DUST, THERE IS A CHANCE OF AFTERNOON  
THUNDERSTORMS EACH DAY ALONG THE INTERIOR AND WESTERN PUERTO RICO,  
ALTHOUGH RAINFALL ACCUMULATIONS ARE NOT EXPECTED TO BE TOO  
SIGNIFICANT OR LONG-LASTING.  
   
LONG TERM...MONDAY TROUGH FRIDAY
 
 
FROM MONDAY INTO TUESDAY, AN UPPER-LEVEL CUT-OFF LOW WILL POSITION  
ITSELF OVER HISPANIOLA, PROVIDING ENOUGH INSTABILITY ALOFT TO  
SUPPORT SOME CONVECTIVE DEVELOPMENT ACROSS THE REGION. HOWEVER,  
DESPITE THIS INSTABILITY, MOISTURE LEVELS ACROSS PUERTO RICO AND  
THE U.S. VIRGIN ISLANDS WILL REMAIN LIMITED, PARTICULARLY AT MID  
TO UPPER LEVELS, WHERE RELATIVE HUMIDITY VALUES ARE FORECAST TO  
STAY LOW. THIS LACK OF DEEP MOISTURE WILL PREVENT WIDESPREAD OR  
LONG-LASTING SHOWER ACTIVITY. AT THE SURFACE, CONDITIONS WILL BE  
DRIVEN BY A SURFACE HIGH-PRESSURE SYSTEM TO THE NORTH OF THE  
REGION, PROMOTING EASTERLY WINDS FROM MONDAY INTO EARLY TUESDAY.  
BY LATE TUESDAY, AS THE BROAD SURFACE HIGH EXPANDS AND  
ESTABLISHES ITSELF OVER THE CENTRAL ATLANTIC, SURFACE WINDS WILL  
GRADUALLY SHIFT FROM THE SOUTHEAST. ACCORDING TO THE GALVEZ-  
DAVISON INDEX (GDI), THE BEST CHANCE FOR NOTABLE CONVECTIVE  
DEVELOPMENT WILL OCCUR ON TUESDAY, WITH THE POTENTIAL FOR A FEW  
ISOLATED THUNDERSTORMS DURING THE AFTERNOON HOURS. THE FOCUS OF  
THE SHOWERS WILL BE ON THE NORTHWESTERN QUADRANT LEAVING THE REST  
OF THE ISLANDS WITH LESS POTENTIAL TO OBSERVED SHOWER ACTIVITY.  
 
BY WEDNESDAY, A NEW PLUME OF SAHARAN DUST WILL BEGIN TO MOVE INTO  
THE REGION, LIMITING AFTERNOON SHOWER DEVELOPMENT DESPITE  
LINGERING INSTABILITY. THESE DUST PARTICLES ARE FORECAST TO  
PERSIST THROUGH FRIDAY, CONTRIBUTING TO HAZY SKIES, REDUCED AIR  
QUALITY, AND LIMITED RAINFALL ACTIVITY ACROSS THE ISLANDS.  
ALTHOUGH SOME LOW-LEVEL MOISTURE MAY BECOME TRAPPED BENEATH THE  
DUST LAYER, ANY RESULTING SHOWERS WILL BE BRIEF AND ISOLATED.  
SURFACE WINDS WILL REMAIN FROM THE SOUTHEAST THROUGH MIDWEEK AS  
THE HIGH MAINTAINS ITS POSITION OVER THE CENTRAL ATLANTIC, HELPING  
TO SUSTAIN VARIABLE BUT GENERALLY SUPPRESSED AFTERNOON CONVECTION.  
OVERALL, THE WEATHER PATTERN FOR THE LATTER HALF OF THE WEEK WILL  
FEATURE PARTLY CLOUDY SKIES, HAZY CONDITIONS, AND LIMITED RAINFALL  
POTENTIAL.  
 

 
   
AVIATION
 
 
(06Z TAFS)  
 
MOSTLY VFR CONDITIONS EXPECTED TO PREVAIL EARLY IN THE DAY. SHRA AND  
TSRA ARE EXPECTED AFTER 17Z FOR THE WESTERN CORDILLERA CENTRAL AND  
TJBQ, WITH MOUNTAIN OBSCURATION AND PERIODS OF REDUCED VIS AND LOW  
CEILINGS. A TROPICAL WAVE WILL BRING ADDITIONAL SHRA INTO THE AREA,  
BUT WITH LITTLE IMPACTS TO OPERATIONS. HZ DUE TO SAHARAN DUST WILL  
MOVE INTO THE USVI TERMINALS AFTER 13Z, AND GRADUALLY PROGRESSING  
INTO PR. VIS ARE EXPECTED TO REMAIN ABOVE 6SM. WINDS WILL BE FROM  
THE SE AT 11-16 KTS, WITH STRONGER GUSTS.  
 

 
   
MARINE
 
 
A BROAD SURFACE HIGH PRESSURE OVER THE CENTRAL ATLANTIC AND A  
TROPICAL WAVE WILL CONTINUE TO RESULT IN MODERATE TO FRESH  
EASTERLY WINDS ACROSS THE REGION. THEREFORE, WIND-DRIVEN SEAS WILL  
RESULT IN CHOPPY MARINE CONDITIONS ACROSS THE OFFSHORE ATLANTIC  
WATERS AND THE OFFSHORE CARIBBEAN WATERS. FOR TODAY INTO MONDAY,  
SAHARAN DUST PARTICLES WILL BE IN PLACE, RESULTING IN HAZY SKIES  
AND LIMITED SHOWER ACTIVITY.  
 

 
   
BEACH FORECAST
 
 
GOOD NEWS FOR TODAY 4TH OF JULY, ALL THE COASTAL AREAS OF PUERTO  
RICO AND THE US VIRGIN ISLANDS THE RISK OF RIP CURRENT WILL REMAIN  
LOW AND IT WILL PERSIST LOW FOR AT LEAST SUNDAY WHEN TURN MODERATE  
TO ST. CROIX. THE RISK OF RIP CURRENT WILL BECOME MODERATE FOR THE  
NORTHWESTERN SECTIONS OF PUERTO RICO BY MONDAY.  
 

 
   
SJU WATCHES/WARNINGS/ADVISORIES
 
 
PR...HEAT ADVISORY FROM 10 AM THIS MORNING TO 4 PM AST THIS AFTERNOON  
FOR PRZ001>005-007-008-010-011.  
 
VI...NONE.  
AM...NONE.  

 
 

 
 
SHORT TERM & AVIATION...ERG  
LONG TERM & MARINE....LIS  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab PR Page Main Text Page