286
FXCA62 TJSJ 141512
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1112 AM AST THU AUG 14 2025
UPDATE
RELATED TO THE LATEST TRAJECTORY AND INTENSITY FORECAST FROM NHC
FOR TROPICAL STORM ERIN, POTENTIAL IMPACTS HAVE NOT CHANGED MUCH.
HOWEVER, POPS AND QPF WERE ADJUSTED TO REFLECT THE POTENTIAL
INDIRECT IMPACTS OF ERIN DUE TO ITS FEEDER BANDS AS IT MOVES
NORTHEAST TO NORTH NORTHWEST FROM SATURDAY THROUGH MONDAY.
EXPECTED RAINFALL AMOUNTS OF 2-3 INCHES IN NORTHWESTERN PUERTO
RICO AND 2-4 INCHES ACROSS SOUTHERN AND EASTERN PUERTO RICO, AS
WELL AS VIEQUES, CULEBRA, AND THE USVI, WITH LOCALLY HIGHER
AMOUNTS. THIS COULD PROMOTE URBAN AND SMALL STREAM FLOODING,
LOCALIZED FLASH FLOODING, AND LANDSLIDES.
THE HEAT THREAT EXPECTED FOR THIS UPCOMING WEEKEND WILL LIKELY
REMAIN LIMITED, AS EXTENSIVE CLOUD COVERAGE FROM TROPICAL STORM
ERIN HINDERS MAXIMUM TEMPERATURES FOR THE MOST PART. HOWEVER, AN
ELEVATED TO EVEN SIGNIFICANT HEAT THREAT IS LIKELY BY EARLY NEXT
AS ERIN MOVES NORTH NORTHWEST OF THE REGION, INDUCING SOUTHERLY
WINDS AND BRINGING WARM AIR TO THE ISLANDS.
PREV DISCUSSION
/ISSUED 532 AM AST THU AUG 14 2025/
KEY MESSAGES...
* A HEAT ADVISORY IS IN EFFECT FOR THE URBAN AND COASTAL AREAS OF
PUERTO RICO AND THE U.S. VIRGIN ISLANDS FROM 10 AM AST THIS
MORNING THROUGH 5 PM AST THIS AFTERNOON.
* FOR THE U.S. VIRGIN ISLANDS, LIGHT TO MODERATE SHOWERS DURING
THE MORNING HOURS, WHILE CONVECTION ACTIVITY WILL INCREASE
FLOODING RISK ACROSS INTERIOR AND WESTERN SECTIONS OF PUERTO
RICO IN THE AFTERNOON.
* AN INDUCED SURFACE PERTURBATION WILL BRING FREQUENT PASSING
SHOWERS ACROSS THE U.S. VIRGIN ISLANDS AND WINDWARD SECTIONS OF
PUERTO RICO EARLY FRIDAY MORNING.
* TROPICAL STORM ERIN IS FORECAST TO MOVE NEAR THE ISLANDS BY
SATURDAY. AS A RESULT, RESIDENTS CAN EXPECT HAZARDOUS MARINE
AND COASTAL CONDITIONS FROM SATURDAY THROUGH MONDAY. PLEASE
STAY TUNED FOR FURTHER WEATHER UPDATES ON THIS TROPICAL SYSTEM.
SHORT TERM...TODAY THROUGH SATURDAY
A SURGE OF MOISTURE EMBEDDED IN THE TRADES PRODUCED SCATTERED TO
NUMEROUS SHOWERS ACROSS THE REGIONAL WATERS OF PUERTO RICO AND THE
US VIRGIN ISLANDS. THIS ACTIVITY MOVED INLAND ACROSS THE USVI AND
WINDWARD LOCATIONS OF PR OCCASIONALLY OVERNIGHT. WINDS WERE MAINLY
FROM THE EAST TO EAST-NORTHEAST AT 10 MPH OR LESS, BUT WITH BRIEF
GUSTY WINDS, AND UNDER LAND BREEZE FLUCTUATION ACROSS THE LEEWARD
SIDE OF THE ISLANDS. ADDITIONALLY, AND ONCE AGAIN, WE OBSERVED
ANOTHER NIGHT WITH WARMER-THAN-NORMAL MINIMUM TEMPERATURES.
ADDITIONAL MOISTURE EMBEDDED IN THE TRADES WILL BRING ANOTHER DAY
WITH OCCASIONAL SHOWERS ACROSS THE WINDWARD LOCATIONS IN THE USVI
AND PR. AT THE SAME TIME, THIS MOISTURE WILL COMBINE WITH THE ABOVE-
NORMAL MAXIMUM TEMPERATURES TO RESULT IN ANOTHER DAY WITH WARM TO
HOT HEAT INDICES, ESPECIALLY ACROSS THE URBAN COASTAL LOCATIONS IN
PR AND THE US VIRGIN ISLANDS. AS A RESULT, A HEAT ADVISORY IS IN
EFFECT FROM 10 AM AST TO 5 PM AST. THIS LEVEL OF HEAT AFFECTS MOST
INDIVIDUALS SENSITIVE TO HEAT, ESPECIALLY THOSE WITHOUT EFFECTIVE
COOLING AND/OR ADEQUATE HYDRATION. BY THE AFTERNOON, ANOTHER ROUND
OF STRONG CONVECTION WILL RESULT IN FLOODING RAINS ACROSS THE
INTERIOR AND WESTERN LOCATIONS OF PR, AND DOWNWIND FROM THE USVI.
WESTERN PR HAS AN ELEVATED RISK OF OBSERVING FLOODING RAINS TODAY,
WHILE THE USVI HAS A LIMITED RISK OF FLOODING RAINS.
ON FRIDAY, AN INDUCED SURFACE PERTURBATION WILL BRING FREQUENT
PASSING SHOWERS ACROSS THE USVI AND WINDWARD SECTIONS OF PR EARLY
FRIDAY MORNING. HOWEVER, THE WARM TO HOT SPELL WILL CONTINUE BY MID-
MORNING INTO THE AFTERNOON, AS THE PERTURBATION EXITS THE REGION,
LEAVING ITS LINGERING MOISTURE OVER US. THE PERTURBATION WILL BE
FOLLOWED BY AN AREA OF SUBSIDENCE AHEAD OF ERIN, WHICH WILL LIMIT
RAIN ACTIVITY BEFORE THE ONSET OF THE EXTERNAL BANDS OF THE SYSTEM,
WHICH ARE FORECAST TO ARRIVE AS EARLY AS SATURDAY MORNING AND MOST
LIKELY AROUND SATURDAY EVENING. THIS PATTERN WILL RESULT IN SQUALLY
WEATHER, WHICH COULD CAUSE STRONG GUSTY WINDS (IN SOME INSTANCES,
THESE SQUALLS COULD BRING TROPICAL STORM WIND FORCE) AND OCCASIONAL
PERIODS OF HEAVY RAIN.
LONG TERM...SUNDAY THROUGH THURSDAY...
THE LONG-TERM FORECAST REMAINS ON TRACK, AS THE WET AND UNSETTLED
PATTERN IS EXPECTED TO CONTINUE. BASED ON THE LATEST NHC'S
TRAJECTORY AND INTENSITY FORECAST FOR ERIN, ITS CENTER SHOULD MOVE
OFF TO THE NORTHEAST OF THE NORTHEAST CARIBBEAN AROUND EARLY
SUNDAY MORNING. HOWEVER, IF THIS FORECAST VALIDATES, ERIN'S
EXTERNAL RAIN BANDS COULD TURN MORE FREQUENT AS ERIN APPROACHES
THE ISLANDS FROM A DISTANCE. NEVERTHELESS, THE PROXIMITY OF ERIN
WILL SHIFT FROM THE SOUTH TO THE SOUTHWEST AROUND SUNDAY, POOLING
PLENTY OF TROPICAL MOISTURE OVER THE ISLANDS THROUGH MONDAY.
BASED ON THE LATEST MODEL GUIDANCE, PRECIPITABLE WATER VALUES ARE
LIKELY TO EXCEED THE 75TH PERCENTILE (2.0 - 2.2 INCHES, WITH LOW
CHANCE OF REACHING 2.4 INCHES), WELL ABOVE CLIMATOLOGICAL NORMAL.
UNDER A S-SW WIND FLOW, IT IS LIKELY TO OBSERVE AN ADVECTIVE
PATTERN DURING THE MORNING HOURS, WITH SHOWERS AND THUNDERSTORMS
AFFECTING WINDWARD SECTIONS OF THE LOCAL ISLANDS, BUT THE CONCERN
REMAINS HIGH FOR THE INTERIOR AND NORTHERN PORTIONS OF PUERTO RICO
AND THE U.S. VIRGIN ISLANDS. DUE TO CONTINUOUS SHOWER ACTIVITY
AND SATURATED SOILS, THE POTENTIAL TO OBSERVE URBAN FLOODING,
LANDSLIDES ALONG STEEP TERRAINS, AND RIVER FLOODING WILL INCREASE.
WE EXPECT FUTURE ADJUSTMENTS TO THE FORECAST DUE TO THE EXISTING
ERROR ASSOCIATED WITH DAY 4 IN THE FORECAST. THUS, WE ENCOURAGE
EVERYONE IN PUERTO RICO AND THE US VIRGIN ISLANDS TO KEEP AN EYE
ON ERIN OVER THE NEXT FEW DAYS, AS THE INTENSITY AND TRACK
FORECAST WILL UNDERGO CHANGES, AND OUR WEATHER FORECAST DEPEND ON
ITS PROGRESS. STAY TUNED FOR FURTHER UPDATES.
BY TUESDAY NIGHT, A SURFACE HIGH PRESSURE OVER THE CENTRAL
ATLANTIC SHOULD STRENGTHEN, PROMOTING WINDS FROM THE SOUTHEAST.
BASED ON THE DETERMINISTIC GUIDANCE OF THE GFS AND ECMWF, PWAT
WILL LIKELY DECREASE TO SEASONAL VALUES (1.6 - 1.8 INCHES).
NEVERTHELESS, MODEL SOLUTIONS CURRENTLY AGREE THAT AN UPPER-LEVEL
TROUGH WILL LIKELY APPROACH THE CWA BY WEDNESDAY MORNING,
INCREASING MOISTURE CONTENT ONCE AGAIN.
WITH A S-SE WIND FLOW, ABUNDANT MOISTURE, AND ABOVE- NORMAL 925
MB TEMPERATURES, THE HEAT RISK IS LIKELY TO INCREASE EARLY NEXT
WEEK. THE MOST LIKELY SCENARIO WOULD BE HEAT INDEXES ACROSS URBAN
AND COASTAL AREAS REACHING HEAT ADVISORY OR HEAT WARNING CRITERIA,
BUT THIS WILL DEPEND ON THE BEHAVIOR OF ERIN DURING THAT PERIOD.
AVIATION...
(06Z TAFS)
EXPECT VFR CONDITIONS THROUGH MUCH OF THE FORECAST PERIOD.
OCCASIONAL SHRA WILL ARRIVE ACROSS IST/ISX/JSJ THROUGHOUT THE DAY,
WITH SHRA/TSRA DEVELOPING ACROSS THE INTERIOR AND WESTERN SECTIONS
OF PR BY THIS AFTERNOON (14/16-23Z). THIS TSRA COULD IMPACT JBQ AND
THE VCTY OF JPS. EXPECT E-ENE WINDS AT AROUND 10 KT THROUGH AT LEAST
14/13Z, AFTER THAT, THEY WHEN WILL RANGE BETWEEN 15-20 KT WITH
HIGHER GUSTS AND SEA BREEZE VARIATIONS.
MARINE...
AN INDUCED EASTERLY PERTURBATION CROSSING THE LESSER ANTILLES WILL
MOVE ACROSS PR AND THE USVI TOMORROW, INCREASING SHOWER ACTIVITY,
LOCAL WINDS, AND SEAS MAINLY ACROSS THE CARIBBEAN SEA. THE EXTERNAL
BANDS OF ERIN, PRODUCING SQUALLY WEATHER, WILL ARRIVE AS EARLY AS
SATURDAY MORNING AND MOST LIKELY AROUND SATURDAY EVENING, AS ERIN'S
NHC TRAJECTORY FORECAST MOVES IT OFF TO THE NORTHEAST AWAY FROM
PR/USVI OVER THE ATLANTIC OCEAN THROUGHOUT THE WEEKEND. ERIN'S
HAZARDOUS SWELL ACTION WILL IMPACT THE ATLANTIC AND CARIBBEAN
PASSAGES FROM SATURDAY EVENING THROUGH AT LEAST EARLY NEXT WEEK.
MARINERS AND VISITORS ARE URGED TO CLOSELY MONITOR THE EVOLUTION OF
ERIN.
BEACH FORECAST...
THE RISK OF RIP CURRENTS CONTINUES ACROSS THE NORTH AND EAST-
FACING BEACHES IN PUERTO RICO AND ST. CROIX IN THE U.S. VIRGIN
ISLANDS. THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS THE LOCAL
WATERS AND MAY APPROACH SOME COASTAL AREAS DURING THE MORNING.
ADDITIONALLY, SHOWERS AND THUNDERSTORMS OVER INTERIOR AND WESTERN
PUERTO RICO COULD MOVE OVER COASTAL AREAS AS WELL. BEACHGOERS
MUST EXERCISE CAUTIONS AND STAY WEATHER ALERT.
IMPORTANT: ERIN'S SWELL ACTION COULD DETERIORATE MARINE AND
COASTAL CONDITIONS, CREATING LIFE-THREATENING RIP CURRENTS FOR
THIS UPCOMING WEEKEND. RESIDENTS AND VISITORS ARE URGE TO AVOID
THE COASTAL AREAS FROM SATURDAY AFTERNOON TROUGH MONDAY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY UNTIL 5 PM AST THIS AFTERNOON FOR PRZ001>005-007-
008-010>013.
VI...HEAT ADVISORY UNTIL 5 PM AST THIS AFTERNOON FOR VIZ001-002.
AM...NONE.
CVB/GRS
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