768
FXCA62 TJSJ 180901
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
501 AM AST FRI JUL 18 2025
KEY MESSAGES
* SLIGHTLY HAZY SKIES TODAY WITH SHOWERS AND ISOLATED THUNDERSTORMS,
PARTICULARLY DURING THE AFTERNOON OVER SECTORS OF THE INTERIOR,
WESTERN AND SOUTHWESTERN PR. FLOOD RISK FROM LIMITED TO
ELEVATED.
* A HEAT ADVISORY IS IN EFFECT BETWEEN 10 AM AND 5 PM AST ALONG
COASTAL URBAN AREAS OF PUERTO RICO.
* THERE IS A MODERATE RISK OF LIFE-THREATENING RIP CURRENTS ACROSS
THE NORTHERN AND EASTERN BEACHES OF PUERTO RICO, CULEBRA, AND
ST.CROIX TODAY. A LOW RISK IS MAINLY EXPECTED DURING THE
WEEKEND THROUGH EARLY NEXT WEEK.
SHORT TERM...TODAY THROUGH SUNDAY
A DRIER AIR MASS LIMITS RAIN ACTIVITY ACROSS THE ISLANDS, WHILE THE
DOPPLER RADAR DETECTED SCATTERED SHOWERS ACROSS THE LOCAL WATERS.
SKIES WERE MOSTLY CLEAR TO PARTLY CLOUDY, WITH SOME HAZE DUE TO THE
SAHARAN AIR LAYER MOVING ACROSS. WARMER-THAN-NORMAL MINIMUM
TEMPERATURES WERE OBSERVED ONCE AGAIN, WITH TEMPERATURES RANGING
FROM THE UPPER 60S IN THE MOUNTAINS TO THE UPPER 70S OR LOW 80S IN
COASTAL URBAN AREAS. WINDS WERE MAINLY FROM THE EAST AT 10 MPH OR
LESS, WITH VARIATIONS DUE TO LAND BREEZES.
AS THE DAY BEGINS WITH WARMER-THAN-NORMAL TEMPERATURES UNDER THE
INFLUENCE OF AN EXITING SAHARAN AIR LAYER, YOU CAN EXPECT WARM TO
HOT HEAT INDICES DURING THE PEAK HEATING TODAY. THEREFORE, A HEAT
ADVISORY IS IN EFFECT BETWEEN 10 AM AND 5 PM AST ALONG THE COASTAL
URBAN AREAS IN PUERTO RICO. ADDITIONALLY, THE ISLANDS OF VIEQUES,
CULEBRA, AND THE US VIRGIN ISLANDS CAN ALSO EXPECT EXCESSIVE HEAT
INDEX VALUES.
THE AVAILABLE MOISTURE, COMBINED WITH LOCAL EFFECTS, LINGERING
CONCENTRATIONS OF DUST PARTICLES, AND SEA BREEZES, WILL PROMOTE
STRONG ISOLATED AFTERNOON THUNDERSTORMS ACROSS THE INTERIOR AND
WESTERN SECTIONS OF PR, AS WELL AS SHOWERS DOWNWIND FROM THE US
VIRGIN ISLANDS. AN ELEVATED RISK OF FLOODING DUE TO HEAVY DOWNPOURS
ASSOCIATED WITH THE AFTERNOON THUNDERSTORMS WILL BE PRESENT FOR THE
INTERIOR AND SOUTHWESTERN SECTIONS OF PR.
ALTHOUGH WE OBSERVED SOME DISCREPANCIES REGARDLESS OF THE POSITION
OF A RETROGRADING TUTT LOW AND THE MOISTURE POOLING OVER THE
ISLANDS, SATURDAY PRESENT A GOOD CHANCE TO SEE THE FORMATION OF
THUNDERSTORMS ACROSS THE ISLANDS. THIS TUTT LOW WILL INDUCE A
SURFACE TROUGH THAT WILL SWING BY THE ISLANDS ON SATURDAY, LEAVING
A TRAILING OF MOISTURE ON SUNDAY. THUS, AT THIS TIME WE ARE
FORECASTING AN ACTIVE AFTERNOON WITH SOME ISOLATED TO SCATTERED
THUNDERSTORMS MAINLY ACROSS PORTIONS OF PR, AND THE USVI MAY HAVE
A GOOD POTENTIAL TO OBSERVE OCCASIONAL PERIODS OF SHOWERY WEATHER.
ADDITIONALLY, A PERIOD OF WARM TO HOT HEAT INDICES IS EXPECTED TO
PERSIST ON SATURDAY AND SUNDAY, ESPECIALLY IN LOCATIONS WITHOUT
RAIN ACTIVITY DURING THE AFTERNOON. SUNDAY LOOKS LIKE A TYPICAL
SUMMER DAY IN THE TROPICS.
LONG TERM...MONDAY THROUGH FRIDAY
AT THE BEGINNING OF THE LONG-TERM PERIOD, A MID TO UPPER LEVEL RIDGE
BUILDING FROM THE CENTRAL ATLANTIC INTO THE NORTHEASTERN CARIBBEAN
WILL SHIFT FURTHER WEST AND DISPLACE THE PREVAILING TROUGH PATTERN.
WINDS WILL SHIFT MORE FROM THE EAST. IT SEEMS THAT MONDAY WILL BE
THE DAY WITH THE LEAST RAIN AND THE MOST STABLE CONDITIONS OF THE
FORECAST PERIOD. MODELS SUGGEST PRECIPITABLE WATER WILL DROP TO
AROUND 1.3 TO 1.4 INCHES, WHICH IS BELOW NORMAL VALUES. 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 RANGE FROM NONE TO LIMITED AT THE START
OF THE WEEK. FROM MONDAY NIGHT ONWARD, ANOTHER TUTT LOW WILL APPROACH
THE REGION, BRINGING A WIND SURGE AND A SERIES OF DISTURBANCES WITH
PATCHES OF MOISTURE FROM TUESDAY THROUGH THURSDAY, LIKELY ACCOMPANIED
BY SOME SAHARAN DUST THAT COULD ENHANCE THUNDERSTORMS DEVELOPMENT
DURING THE AFTERNOONS. AT THIS TIME, EXPECT VARIABLE WEATHER CONDITIONS
DURING THOSE DAYS AND BREEZY TO WINDY EASTERLY WINDS, WITH EARLY
MORNING CONVECTION BETWEEN THE USVI AND EASTERN SECTIONS OF PUERTO
RICO, FOLLOWED BY AFTERNOON CONVECTION WITH ISOLATED THUNDERSTORMS
OVER PARTS OF THE INTERIOR AND WESTERN PUERTO RICO. FLOOD RISK SHOULD
RANGE FROM LIMITED TO ELEVATED EACH AFTERNOON IN THOSE AREAS. MODELS
SUGGEST PRECIPITABLE WATER WILL FLUCTUATE AROUND 1.6 TO 1.7 INCHES,
WHICH IS CONSIDERED NEAR SEASONAL VALUES. ADDITIONALLY, WARM TO HOT
TEMPERATURES WILL CONTINUE TO DOMINATE DURING THIS PERIOD, AS INDICATED
BY ABOVE- NORMAL 925 MB TEMPERATURES. THIS WILL LIKELY TRIGGER HEAT
ADVISORY CONDITIONS ACROSS MOST COASTAL AND URBAN AREAS OF PUERTO RICO
EACH DAY. 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.
TOWARD THE END OF THE PERIOD, THE LATEST GUIDANCE SUGGESTS THE ARRIVAL
OF A TROPICAL WAVE ALONG WITH WELL ABOVE-NORMAL PRECIPITABLE WATER.
UPPER-LEVEL DYNAMICS WILL LIKELY SUPPORT AN UNSTABLE WEATHER PATTERN
BEGINNING FRIDAY. STAY TUNED OVER THE NEXT FEW DAYS FOR FORECAST
UPDATES AND ADJUSTMENTS, AS WE ARE STILL ONE WEEK OUT AND
CONFIDENCE REMAINS LOW.
AVIATION
(06Z TAFS)
ANOTHER TYPICAL SUMMER DAY WITH VFR CONDITIONS TODAY. HOWEVER, HAZY
SKIES WILL PERSIST THROUGH EARLY THIS AFTERNOON. THEN, SHRA/TSRA
WILL DEVELOP ALONG THE CORDILLERA CENTRAL AND W/SW PR BETWEEN 18/15-
23Z. EXPECT CALM TO LIGHT AND VARIABLE WINDS THROUGH 18/13Z, THEN
WINDS WILL RETURN FROM THE E/ENE AT 15-20 KT WITH HIGHER GUSTS NEAR
25-30KT AND SEA BREEZE VARIATIONS.
MARINE
A SURFACE HIGH PRESSURE OVER THE ATLANTIC WILL MAINLY PROMOTE MODERATE
EASTERLY WINDS OVER SEVERAL DAYS, BECOMING MODERATE TO FRESH AGAIN
AROUND TUESDAY NEXT WEEK. SHOWERS AND ISOLATED THUNDERSTORMS ARE
EXPECTED ACROSS THE WESTERN WATERS OF PUERTO RICO AND THE MONA PASSAGE
THIS AFTERNOON. A SAHARAN AIR LAYER WILL RESULT IN HAZY SKIES THROUGH
TONIGHT, PARTICULARLY ACROSS THE CARIBBEAN WATERS. AN INDUCED SURFACE
TROUGH WILL INCREASE SHOWER ACTIVITY ACROSS THE WATERS DURING THE
WEEKEND.
BEACH FORECAST
TODAY, THERE IS A MODERATE RISK OF LIFE-THREATENING RIP CURRENTS ACROSS
THE NORTHERN AND EASTERN BEACHES OF PUERTO RICO, CULEBRA, AND ST.CROIX.
A LOW RISK IS MAINLY EXPECTED DURING THE WEEKEND THROUGH EARLY NEXT
WEEK, WITH SOME EXCEPTIONS ACROSS NORTHERN EXPOSED BEACHES. LIFE-
THREATENING RIP CURRENTS MAY STILL OCCUR, ESPECIALLY NEAR GROINS,
JETTIES, REEFS, AND PIERS. INCREASING WINDS STARTING AROUND TUESDAY
AND WEDNESDAY MAY ONCE AGAIN RAISE THE RISK TO MODERATE ALONG MOST
LOCAL BEACHES, ALWAYS SWIM NEAR A LIFEGUARD AND FOLLOW THE ADVICE OF
LOCAL BEACH PATROLS AND FLAG WARNING SYSTEMS.
HEAT INDEX VALUES LIKELY EXCEEDING 100°F EACH DAY. STAY WELL HYDRATED,
SEEK SHADE FREQUENTLY, AND AVOID OUTDOOR ACTIVITY DURING PEAK SUN HOURS.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY FROM 10 AM THIS MORNING TO 5 PM AST THIS AFTERNOON
FOR PRZ001>005-007-008-010-011.
VI...NONE.
AM...NONE.
SHORT TERM/AVIATION...CAM
LONG TERM/MARINE/BEACH FORECAST...YZR
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