725
FXCA62 TJSJ 301743
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
143 PM AST MON JUN 30 2025
KEY MESSAGES
* MODERATE CONCENTRATIONS OF SAHARAN DUST THROUGH EARLY TUESDAY.
ANOTHER PLUME OF SAHARAN DUST CAN REACH THE REGION TO END THE
WEEK.
* BREEZY WINDS WILL SUSTAIN CHOPPY SEAS AND MAINTAIN A MODERATE
RISK OF RIP CURRENTS ALONG EXPOSED BEACHES THROUGH MIDWEEK.
* ANOTHER TROPICAL WAVE IS FORECAST TO AFFECT THE ISLANDS ON
FRIDAY, AGAIN INCREASING SHOWER AND THUNDERSTORM ACTIVITY.
SHORT TERM...TONIGHT THROUGH WEDNESDAY
CALM AND STABLE WEATHER DOMINATED THE REGION TODAY. SKIES WERE
HAZY DUE TO MODERATE CONCENTRATIONS OF SAHARAN DUST. DAYTIME HIGHS
REACHED THE UPPER 80S TO LOW 90S ALONG THE COASTS, WHILE MOUNTAIN
AREAS REMAINED IN THE UPPER 70S TO LOW 80S. WINDS WERE FROM THE
EAST AT 9 TO 25 MPH, WITH THE STRONGEST OBSERVED ALONG COASTAL
AREAS.
DRY AND STABLE CONDITIONS WILL PERSIST TONIGHT INTO TUESDAY, UNDER
THE INFLUENCE OF A MID-LEVEL RIDGE AND A STRONG SURFACE HIGH-
PRESSURE SYSTEM OVER THE CENTRAL ATLANTIC. THESE FEATURES WILL
CONTINUE TO SUPPORT BREEZY EASTERLY WINDS, AND LIMITED SHOWER
ACTIVITY ACROSS THE REGION.
A WEAK SURFACE DISTURBANCE IS FORECAST TO APPROACH THE REGION LATE
TUESDAY NIGHT INTO WEDNESDAY, BRINGING OCCASIONAL PATCHES OF
MOISTURE EMBEDDED IN THE TRADE WINDS. THIS COULD LEAD TO SLIGHTLY
INCREASED CLOUD COVER AND ISOLATED SHOWERS FROM TIME TO TIME.
THE MID-LEVEL RIDGE WILL BEGIN TO WEAKEN AS A MID-TO-UPPER-LEVEL
LOW DEEPENS TO THE NORTHEAST. ALTHOUGH THIS CHANGE MAY ALLOW FOR
SOME VERTICAL DEVELOPMENT, MID-LEVEL HUMIDITY WILL REMAIN BELOW
AVERAGE, WHICH MAY LIMIT MORE WIDESPREAD CONVECTION. NONETHELESS,
MARGINAL INSTABILITY AND AVAILABLE MOISTURE COULD TRIGGER A FEW
ISOLATED SHOWERS MAINLY OVER WESTERN PUERTO RICO DURING THE
AFTERNOON.
LONG TERM...THURSDAY THROUGH MONDAY
ALTHOUGH THURSDAY WILL START WITH BELOW NORMAL CONCENTRATIONS OF
PRECIPITABLE WATER (PWAT), PERIPHERAL MOISTURE FROM AN APPROACHING
TROPICAL WAVE WILL INCREASE PWAT TO AROUND 1.8 INCHES BY THURSDAY
AFTERNOON AND EVENING. A SURFACE HIGH OVER THE ATLANTIC WILL
PROMOTE UP TO BREEZY EAST TO EAST-SOUTHEAST STEERING FLOW THROUGH
SATURDAY, BACKING THEREAFTER. THE DIURNAL SHOWER PATTERN WILL BE
LIMITED FOR MOST OF THURSDAY, WITH PASSING MORNING SHOWERS AND
AFTERNOON SHOWERS AND STRONGER SHOWERS OVER WESTERN PR. AVAILABLE
MOISTURE WILL REMAIN BELOW 850 MB ON THURSDAY. HOWEVER, DEEPER
MOISTURE WILL REACH THE AREA ON FRIDAY AS PWAT VALUES INCREASE TO
2 INCHES OR MORE. THEREFORE, FRIDAY IS EXPECTED TO BE THE WETTEST
DAY, AS A TROPICAL WAVE CROSSES THE ISLANDS AND A RETROGRADING
MID- TO UPPER-LEVEL LOW ALSO APPROACHES. THIS WILL PROMOTE A BOOST
IN THE DIURNAL PATTERN AND OVERALL INCREASED SHOWER AND T-STORM
ACTIVITY OVER THE REGION, A LIMITED TO ELEVATED FLOODING RISK WILL
REMAIN. GALVEZ-DAVIDSON INDEX (GDI) VALUES ARE FORECASTED TO
REACH +45 ON FRIDAY, MEANING THAT THUNDERSTORM AND HEAVY RAINFALL
POTENTIAL WILL REMAIN. PWAT VALUES WILL QUICKLY DROP TO BELOW
NORMAL BY SATURDAY BEFORE BOUNCING BACK TO AROUND 1.8 IN BY SUNDAY
THROUGH MONDAY AS MOISTURE REMAINS OF THE WAVE ARE CIRCLED BACK
TOWARDS THE ISLANDS BY THE SURFACE HIGH. THE MID- TO UPPER- LEVEL
LOW WILL CONTINUE TO BE NEAR THE ISLANDS DURING THE WEEKEND AND
INTO EARLY NEXT WEEK, PROMOTING SOME INSTABILITY. 925 MB
TEMPERATURES WILL BE ABOVE NORMAL WITH A LIMITED TO POSSIBLY
ELEVATED HEAT RISK EACH AFTERNOON. THE PRESENCE OF SAHARAN DUST,
INCREASING AS THE PERIOD CONTINUES, CAN ALSO SERVE TO LIMIT
NIGHTTIME COOLING. THIS SAHARAN DUST CAN ALSO SERVE AS A LIMITING
FACTOR FOR FRIDAY'S TROPICAL WAVE.
AVIATION
(18Z TAFS)
VFR CONDITIONS EXPECTED ACROSS ALL TAF SITES DURING THE NEXT 24
HOURS. MODERATE CONCENTRATIONS OF SAHARAN DUST WILL RESULT IN HZ,
WITH VISIBILITY OCCASIONALLY REDUCED TO 6 SM. E WINDS WILL
PREVAIL, DECREASING TO 7 TO 12KTS AFTER 30/23Z.
MARINE
MARINERS CAN EXPECT CHOPPY SEAS ACROSS THE LOCAL ATLANTIC AND
CARIBBEAN WATERS DUE PERSISTENT MODERATE TO FRESH EASTERLY WINDS.
SMALL CRAFT SHOULD EXERCISE CAUTION OVER MOST LOCAL WATERS. A MASS
OF DRIER AIR WITH SUSPENDED SAHARAN DUST PARTICLES WILL CONTINUE TO
FILTER INTO THE AREA, MAINTAINING HAZY SKIES THROUGH EARLY TUESDAY.
A TROPICAL WAVE IS FORECAST TO MOVE OVER THE LOCAL WATERS ON
FRIDAY, INCREASING SHOWER AND THUNDERSTORM CHANCES.
BEACH FORECAST
A MODERATE RISK OF RIP CURRENTS (LIFE-THREATENING RIP CURRENTS
ARE POSSIBLE IN THE SURF ZONE) WILL BE IN EFFECT FOR MOST
NORTHERN, SOUTHERN AND EASTERN BEACHES OF PUERTO RICO, AS WELL AS
FOR BEACHES OF CULEBRA, VIEQUES, SOUTHERN ST. JOHN, SOUTHERN ST.
THOMAS AND ALL BUT WESTERN ST. CROIX. ALTHOUGH OTHER AREAS HAVE A
LOW RISK OF RIP CURRENTS, KEEP IN MIND THAT LIFE- THREATENING RIP
CURRENTS OFTEN OCCUR IN THE VICINITY OF GROINS, JETTIES, REEFS,
AND PIERS. THE LOW RISK OF RISK OF RIP CURRENTS WILL SPREAD
TOMORROW TO ST. THOMAS AND ST. JOHN. UP TO A MODERATE RISK OF RIP
CURRENTS WILL REMAIN FOR MOST OF THE PERIOD
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM/MARINE/BEACH FORECAST...MMC
LONG TERM...MRR
AVIATION...DSR/MMC
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