223  
FXCA62 TJSJ 170906  
AFDSJU  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE SAN JUAN PR  
506 AM AST THU JUL 17 2025  
   
KEY MESSAGES  
 
* LINGERING MOISTURE FROM A TROPICAL WAVE WILL RESULT IN SHOWERS AND  
ISOLATED THUNDERSTORMS TODAY, ESPECIALLY ACROSS THE INTERIOR AND  
WESTERN PUERTO RICO DURING THE AFTERNOON HOURS.  
 
* MODERATE TO HIGH CONCENTRATIONS OF SAHARAN DUST PARTICLES ARE  
EXPECTED TO GRADUALLY RETURN TODAY AND PREVAIL THROUGH AT LEAST  
FRIDAY NIGHT, RESULTING IN HAZY SKIES, REDUCED VISIBILITY, AND  
POOR AIR QUALITY.  
 
* LIMITED HEAT RISK TODAY ACROSS URBAN AND COASTAL AREAS OF THE  
ISLANDS. AN ELEVATED HEAT RISK IS EXPECTED OVER THE NEXT FEW DAYS,  
WITH HEAT INDICES LIKELY TO MEET HEAT ADVISORY CRITERIA.  
 
* MODERATE TO LOCALLY FRESH WINDS WILL LEAD TO CHOPPY SEAS AND A  
MODERATE RISK OF RIP CURRENTS THROUGH FRIDAY, AN IMPROVEMENT IS  
EXPECTED DURING THE WEEKEND THROUGH EARLY NEXT WEEK, THEN  
INCREASING WINDS AND A MODERATE RISK RETURNING BY TUESDAY.  
 
 
   
SHORT TERM...TODAY THROUGH SATURDAY  
 
THE SKIES WERE MOSTLY CLEAR ACROSS PR'S WEST, SOUTH AND INTERIOR  
SECTIONS, WHILE NORTH AND EAST WINDWARD LOCATIONS IN PR AND THE US  
VIRGIN ISLANDS OBSERVED PARTLY CLOUDY SKIES. ONCE AGAIN, OVERNIGHT  
MINIMUM TEMPERATURES RANGED FROM THE LOW 60S IN THE MOUNTAINS TO THE  
UPPER-70S OR LOW 80S IN COASTAL URBAN AREAS. THE LINGERING MOISTURE  
OF YESTERDAY'S TROPICAL WAVE CAUSED THE DOPPLER RADAR TO DETECT  
SCATTERED TO NUMEROUS SHOWERS ACROSS THE SURROUNDING WATERS AND  
MOVING INLAND OVER THE USVI AND THE WINDWARD LOCATIONS OF PR. WINDS  
WERE MAINLY FROM THE EAST AT 10 MPH OR LESS, WITH LAND BREEZE AND  
LOCALLY HIGHER GUSTS NEAR SHOWERS.  
 
THE TRAILING MOISTURE OF YESTERDA'S TROPICAL WAVE WILL BRING  
ADDITIONAL ROUNDS OF SHOWERS DURING THE MORNING HOURS, BEFORE THE  
ARRIVAL OF A SAHARAN AIR LAYER (SAL) WITH MODERATE TO HIGH  
CONCENTRATIONS OF SUSPENDED DUST PARTICLES LATER THIS MORNING INTO  
THE FRIDAY. REGARDLESS OF THE EXPECTED HAZY SKIES ASSOCIATED WITH  
THE SAL, THE LINGERING MOISTURE WILL RESULT IN SHALLOW RAIN SHOWERS  
AFFECTING POTIONS OF THE WINDWARD LOCATIONS IN THE USVI AND PR  
DURING THE DAY. THEN, LOCAL EFFECTS, DIURNAL HEATING AND SEA BREEZE  
VARIATIONS WILL PROMOTE THE FORMATION OF AFTERNOON SHOWERS DOWNWIND  
FROM THE USVI AND THE LUQUILLO MOUNTAIN RANGE, AS WELL AS ACROSS THE  
INTERIOR AND WESTERN PR. THIS ACTIVITY WILL RESULT IN PONDING OF  
WATER IN ROADS AND POORLY DRAINED AREAS, WITHOUT RULING OUT THE  
POTENTIAL FOR URBAN AND SMALL STREAM FLOODING. ONE OR TWO INTENSE  
THUNDERSTORMS COULD DEVELOP THIS AFTERNOON, ENHANCED BY THE PRESENCE  
OF THE SUSPENDED DUST PARTICLES. TEMPEREATURE-WISE, WE EXPECT MUGGY,  
WARM TO HOT HEAT INDICES DURING THE MAXIMUM HEATING TODAY, POSING A  
PARTICULAR DANGER TO THE MOST VULNERABLE COMMUNITIES.  
 
MOISTURE WILL ERODE LATER THIS EVENING, AS WE FORECAST THE SAL  
CONCENTRATIONS TO PEAK TONIGHT INTO EARLY FRIDAY MORNING, LIMITING  
RADIATIONAL NIGHTTIME COOLING. THUS, FRIDAY MORNING MAY BEGIN WITH  
WARMER-THAN-NORMAL MINIMUM TEMPERATURES, MAKING IT EASIER TO REACH  
ADVISORY OR EXTREME HEAT WARNING CRITERIA. REGARDLESS, WE CANNOT  
RULE OUT THE TYPICAL RAIN PATTERN, CONSISTING OF PASSING SHOWERS  
ACROSS THE WINDWARD LOCATIONS, FOLLOWED BY AFTERNOON CONVECTION  
ACROSS THE WESTERN PORTIONS OF PR AND DOWNWIND FROM THE US VIRGIN  
ISLANDS.  
 
MODEL GUIDANCE SUGGEST A RETROGRADING TUTT WILL MOVE INTO THE REGION  
AROUND SATURDAY. THIS WILL INDUCE A SURFACE TROUGH, POTENTIALLY  
BRINGING ADDITIONAL TROPICAL MOISTURE OVER PUERTO RICO AND THE US  
VIRGIN ISLANDS. UNDER THESE CONDITIONS, THERE IS A MODERATE CHANCE  
OF WET AND UNSTABLE WEATHER, WHICH COULD LEAD TO A HEIGHTENED RISK  
OF FLOODING RAINS IN THE AFTERNOON AND EVENING ON SATURDAY.  
RESIDENTS AND VISITORS IN PR AND THE USVI SHOULD STAY TUNED FOR  
FURTHER UPDATES REGARDING THIS WEATHER PATTERN.  
   
LONG TERM...SUNDAY THROUGH THURSDAY  
 
AT THE BEGINNING OF THE LONG TERM PERIOD, THE TUTT LOW WILL BE  
POSITIONED TO THE NORTHWEST OF THE REGION ALONG WITH AN INDUCED LOW-  
LEVEL TROUGH EXPECTED TO MOVE ACROSS THE NORTHEASTERN CARIBBEAN  
THROUGH THE WEEKEND, BRINGING SHOWERY WEATHER. THE LATEST MODEL  
GUIDANCE SUGGESTS THAT PRECIPITABLE WATER CONTENT WILL BE UP TO 1.8-  
2.0 INCHES ON SUNDAY, WHICH IS CONSIDERED AVERAGE TO ABOVE AVERAGE.  
IN GENERAL, THESE WEATHER FEATURES WILL ENHANCE EARLY MORNING  
CONVECTION BETWEEN THE USVI AND EASTERN SECTIONS OF PUERTO RICO,  
FOLLOWED BY AFTERNOON THUNDERSTORMS OVER PORTIONS OF THE INTERIOR  
AND WESTERN PUERTO RICO. IT THAT SCENARIO MATERIALIZES, THERE WILL  
BE AN ELEVATED FLOOD RISK ACROSS THE NORTHWESTERN QUADRANT OF PUERTO  
RICO DUE TO A SOUTHEASTERLY WIND FLOW. ON MONDAY, A MID TO UPPER  
RIDGE BUILDING FROM THE CENTRAL ATLANTIC INTO THE NORTHEASTERN  
CARIBBEAN WILL SHIFT FURTHER WEST AND DISPLACE THE TROUGH PATTERN.  
WINDS WILL SHIFT MORE FROM THE EAST. MID-LEVEL MOISTURE IS EXPECTED  
TO DECREASE, AND RAINFALL WILL LIKELY FOLLOW A MORE TYPICAL DIURNAL  
PATTERN DRIVEN BY DAYTIME HEATING AND LOCAL EFFECTS. FLOOD RISK  
SHOULD REMAIN FROM NONE TO LIMITED STARTING THE WEEK. MONDAY NIGHT  
ONWARD, ANOTHER TUTT LOW WILL APPROACH THE REGION BRINGING A WINDS  
SURGE AND A SERIES OF DISTURBANCES WITH PATCHES OF MOISTURE TUESDAY  
AND WEDNESDAY, LIKELY EMBEDDED WITH SAHARAN DUST. AT THE MOMENT,  
THERE IS SOME DISCREPANCIES IN THE GLOBAL MODELS, BUT WE WILL  
CONTINUE TO MONITOR CONDITIONS FOR ANY FORECAST UPDATE. AT THIS  
TIME, EXPECT VARIABLE WEATHER CONDITIONS THOSE DAYS WITH EARLY  
MORNING CONVECTION BETWEEN THE USVI AND EASTERN SECTIONS OF PUERTO  
RICO, FOLLOWED BY CONVECTION WITH ISOLATED THUNDERSTORMS OVER  
PORTIONS OF THE INTERIOR AND WESTERN PUERTO RICO EACH AFTERNOON.  
MODEL SUGGEST PRECIPITABLE WATER WILL FLUCTUATE AROUND 1.6 TO 1.7  
INCHES, WHICH IS CONSIDERED SEASONAL VALUES. BY THURSDAY, MOISTURE  
CONTENT WILL DECREASE TO BELOW AVERAGE VALUES HELPING TO REDUCE  
SHOWER FREQUENCY.  
 
ADDITIONALLY, WARM TO HOT TEMPERATURES ARE ANTICIPATED EACH DAY,  
LIKELY TRIGGERING HEAT ADVISORY CONDITIONS ACROSS MOST COASTAL AND  
URBAN AREAS OF PUERTO RICO. RESIDENTS AND VISITORS ARE ENCOURAGED TO  
STAY HYDRATED, AVOID OUTDOOR ACTIVITY DURING PEAK HEAT HOURS, WEAR  
LIGHT CLOTHING, AND CHECK ON VULNERABLE INDIVIDUALS AND PETS.  
 
 
   
AVIATION  
 
(06Z TAFS)  
 
EXPECT OCCASIONAL SHRA/+SHRA ACROSS THE LOCAL TERMINALS OF E-PR/USVI  
THRU 17/16Z. LOCAL EFFECTS AND SEA BREEZE VARIATIONS WILL RESULT IN  
AFTERNOON SHRA/TSRA ACROSS THE INTERIOR AND WESTERN PR, WHICH COULD  
IMPACT JPS/JBQ OR EVEN JSJ. THIS ACTIVITY COULD RESULT IN BRIEF MVFR  
OR EVEN IFR CONDITIONS, ESPECIALLY BETWEEN 17/16-22Z. HAZY SKIES  
WILL RETURN LATER THIS MORNING, LIMITING VISIBILITIES, FROM 17/12Z,  
PEAKING AFTER 18/00Z. EXPECT CALM TO LIGHT AND VRB WINDS THRU  
17/13Z, THEN E/ESE BETWEEN 15-20 KT THROUGH 17/13Z WITH HIGHER GUSTS  
NEAR 25-30KT AND SEA BREEZE VARIATIONS.  
 
 
   
MARINE  
 
A SURFACE HIGH PRESSURE SYSTEM OVER THE ATLANTIC WILL PROMOTE  
MODERATE TO LOCALLY FRESH EASTERLY WINDS THROUGH TONIGHT ACROSS THE  
REGIONAL WATERS AND LOCAL CARIBBEAN PASSAGES—EXPECT CHOPPY SEAS AS  
WELL. REMNANT MOISTURE FROM A TROPICAL WAVE WILL RESULT IN SHOWERS  
AND ISOLATED THUNDERSTORMS TODAY. ADDITIONALLY, A SAHARAN AIR LAYER  
WILL GRADUALLY ARRIVE TODAY, BRINGING HAZY SKIES THROUGH FRIDAY  
NIGHT. ANOTHER DISTURBANCE IS ANTICIPATED BY THE WEEKEND,  
POTENTIALLY INCREASING SHOWER ACTIVITY ACROSS THE WATERS. WINDS WILL  
REMAIN MODERATE THROUGH THE WEEKEND, INCREASING AGAIN FROM MONDAY  
NIGHT ONWARD.  
 
 
   
BEACH FORECAST  
 
TODAY, THERE IS A MODERATE RISK OF LIFE-THREATENING RIP CURRENTS  
ACROSS THE NORTHERN AND EASTERN BEACHES OF PUERTO RICO, VIEQUES,  
CULEBRA, AND ST. CROIX. A LOW RISK IS EXPECTED ELSEWHERE; HOWEVER,  
LIFE-THREATENING RIP CURRENTS MAY STILL OCCUR, ESPECIALLY NEAR  
GROINS, JETTIES, REEFS, AND PIERS. ALWAYS SWIM NEAR A LIFEGUARD AND  
FOLLOW THE ADVICE OF LOCAL BEACH PATROLS AND FLAG WARNING SYSTEMS.  
 
SIMILAR CONDITIONS WILL LIKELY PERSIST TOMORROW, FRIDAY. AFTER THAT,  
A LOW RISK IS MAINLY EXPECTED THROUGH EARLY NEXT WEEK, WITH SOME  
EXCEPTIONS ACROSS NORTHERN EXPOSED BEACHES. INCREASING WINDS  
STARTING AROUND TUESDAY MAY ONCE AGAIN RAISE THE RISK TO MODERATE.  
 
HAZY CONDITIONS ARE EXPECTED TO PERSIST THROUGH AT LEAST FRIDAY,  
WITH HEAT INDEX VALUES LIKELY EXCEEDING 100°F. STAY WELL HYDRATED,  
SEEK SHADE FREQUENTLY, AND AVOID OUTDOOR ACTIVITY DURING PEAK SUN  
HOURS.  
 
 
   
SJU WATCHES/WARNINGS/ADVISORIES  
 
PR...NONE.  
VI...NONE.  
AM...NONE.  
 
 
 
 
SHORT TERM/AVIATION...CAM  
LONG TERM/MARINE/BEACH FORECAST...YZR  
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