245
FXCA62 TJSJ 201838
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
238 PM AST WED AUG 20 2025
KEY MESSAGES
* LIMITED TO ELEVATED HEAT RISKS WILL CONTINUE FOR PUERTO RICO AND
THE U.S. VIRGIN ISLANDS THROUGH FRIDAY.
* THE NHC IS MONITORING A STRONG TROPICAL WAVE (WITH A MEDIUM
CYCLONIC FORMATION CHANCE) THAT IS FORECAST APPROACH THE ISLANDS
LATE FRIDAY INTO SATURDAY.
* SAHARAN DUST CONCENTRATIONS WILL CONTINUE TONIGHT, THESE
CONCENTRATIONS WILL MAINTAIN HAZY SKIES THROUGH TOMORROW.
* MARINE CONDITIONS WILL DETERIORATE BY THE END OF THE WEEK AS A
NORTHERLY SWELL ARRIVES. BEACHES WILL BE HAZARDOUS ALONG THE
NORTHERN AND WESTERN COAST OF PUERTO RICO, AS WELL AS FOR ST.
THOMAS AND ST. JOHN.
SHORT TERM...TONIGHT THROUGH FRIDAY
SATELLITE AND RADAR OBSERVATIONS INDICATED PREDOMINANTLY SUNNY TO
PARTLY CLOUDY SKIES, WITH HAZY CONDITIONS ACROSS THE REGION. DAYTIME
HIGH TEMPERATURES VARIED NOTABLY, REACHING THE LOWER 80S IN HIGHER
ELEVATIONS AND CLIMBING INTO THE LOW TO MID-90S IN LOWER ELEVATIONS.
HEAT INDEX VALUES SOARED ABOVE 108 DEGREES, WITH SEVERAL STATIONS
RECORDING 112–113 DEGREES OR HIGHER, PARTICULARLY ACROSS THE
COASTAL LOWER ELEVATIONS OF PUERTO RICO, WHERE EXTREME HEAT
WARNINGS WERE IN EFFECT. IN THE U.S. VIRGIN ISLANDS, DAYTIME HIGHS
RANGED FROM 88 TO 95 DEGREES, WITH HEAT INDICES FROM THE MID-100S
TO NEARLY 110F WHERE HEAT ADVISORIES WERE IN EFFECT. WINDS WERE
GENERALLY FROM THE SOUTHEAST TO EAST-SOUTHEAST.
THE SHORT-TERM FORECAST PERIOD FEATURES A GRADUAL TRANSITION BETWEEN
DIFFERENT WEATHER EVENTS, INCLUDING THE SAHARAN AIR LAYER (SAL) AND
A POTENTIALLY VIGOROUS TROPICAL WAVE. FOR THE REMAINDER OF TODAY AND
TOMORROW, HAZY SKIES AND HOT TEMPERATURES WILL PREVAIL. A DRIER-THAN-
NORMAL AIR MASS, WITH PRECIPITABLE WATER VALUES FALLING WELL BELOW
SEASONAL THRESHOLDS, WILL LIMIT CONVECTIVE DEVELOPMENT THROUGH EARLY
FRIDAY.
BY FRIDAY, DUST CONCENTRATIONS ARE EXPECTED TO DECREASE AS THE
VIGOROUS TROPICAL WAVE AND ITS ASSOCIATED MOISTURE FIELD APPROACH
THE REGION, SUPPORTING AN INCREASE IN SHOWERS AND THUNDERSTORM
ACTIVITY. ACCORDING TO THE NATIONAL HURRICANE CENTER, THIS TROPICAL
WAVE HAS A LOW CHANCE OF FORMATION WITHIN THE NEXT 48 HOURS, BUT A
MODERATE PROBABILITY OVER THE NEXT SEVEN DAYS. RESIDENTS ARE ADVISED
TO CONTINUE MONITORING UPDATES, AS ANY CHANGES IN THE WAVE’S
POTENTIAL DEVELOPMENT OR TRACK COULD SIGNIFICANTLY SHIFT THE AREAS
EXPERIENCING THE HEAVIEST SHOWERS AND THUNDERSTORMS, POTENTIALLY
LEADING TO FLOODING.
LONG TERM...SATURDAY THROUGH WEDNESDAY
PREV DISCUSSION
/ISSUED 326 AM AST WED AUG 20 2025/
THE LATEST GUIDANCE CONTINUE TO SUGGEST THAT THE STRONG TROPICAL
WAVE MONITORED BY THE NATIONAL HURRICANE CENTER SHOULD MOVE TO THE
NORTHEAST OF THE LOCAL ISLANDS ON SATURDAY. THIS WAVE WILL SHIFT
THE WINDS FROM THE NORTH, WHICH PLENTY OF MOISTURE REACHING PUERTO
RICO AND THE VIRGIN ISLANDS. SHOWERS AND THUNDERSTORMS ARE
EXPECTED TO STREAM INTO THE REGION, MAINTAINING AND ELEVATED RISK
OF FLOODING, AND A LIMITED RISK OF LIGHTNING. AS THE WAVE LIFTS
INTO THE WESTERN ATLANTIC, THE TRADE WINDS WILL TURN SOUTHEAST AS
THE AIR MASS DRIES. SOME SAHARAN DUST WILL REACH THE ISLAND BY
EARLY IN THE WORKWEEK. TEMPERATURES WILL WARM UP TOO, WITH A HIGH
LIKELIHOOD OF EXPERIENCING HEAT THAT IMPACTS THOSE SENSIBLE TO
HEAT, ESPECIALLY WITHOUT EFFECTIVE COOLING OR ADEQUATE HYDRATION.
BY TUESDAY, AND UPPER LEVEL TROUGH AND A REFLECTION IN THE MID
AND LOW LEVELS WILL MOVE IN. HOWEVER, AT THE SURFACE, MOISTURE
WILL BE BELOW NORMAL. NEVERTHELESS, SOME PASSING SHOWERS CAN BE
SEEN IN THE VICINITY OF THE VIRGIN ISLANDS AND EASTERN PUERTO RICO
AT TIMES TOO. THEN, BY MID-WEEK, THE SURFACE HIGH PRESSURE OVER
THE CENTRAL ATLANTIC WILL CAUSE THE TRADE WINDS TO BE ORIENTED
FROM THE SOUTH-SOUTHEAST. MOISTURE WILL BEGIN TO LIFT FROM
THE CARIBBEAN SEA, ONCE AGAIN INCREASING THE POTENTIAL FOR SHOWERS
AND THUNDERSTORMS.
AVIATION
(18Z TAFS)
EXPECT CALM WX CONDS WITH HAZY SKIES DUE TO EXTENSIVE AREA WITH
SUSPENDED SAHARAN DUST PARTICULATES. WINDS WILL PREVAIL FROM THE SE-
ESE AT 10-15 KT WITH GUSTS UP TO 25 KT IN SEA BREEZE VARIATIONS.
WINDS BCMG E AROUND 10 KT AFT 20/22Z IN LAND BREEZES. WINDS WILL
RETURN FROM THE E AT AROUND 12-18 KT WITH HIGHER GUSTS AND SEA
BREEZE AFT 21/13Z.
MARINE
TONIGHT INTO TOMORROW, LIGHT TO MODERATE SOUTHEASTERLY WINDS WILL
BACK TO BECOME MORE EAST-NORTHEAST. A STRONG TROPICAL WAVE (WITH A
60 PERCENT CYCLONIC FORMATION CHANCE) IS EXPECTED TO APPROACH THE
EASTERN CARIBBEAN ON FRIDAY, INCREASING THUNDERSTORM ACTIVITY IN
GENERAL THROUGH SATURDAY. A LONG PERIOD NORTHERLY SWELL FROM DISTANT
HURRICANE ERIN WILL ARRIVE LATE FRIDAY AND INTO THE WEEKEND,
RESULTING IN HAZARDOUS SEAS FOR THE ATLANTIC WATERS AND PASSAGES.
BEACH FORECAST
THERE IS A MODERATE RISK OF RIP CURRENTS FOR THE NORTHERN BEACHES OF
PUERTO RICO, CULEBRA AND SOME BEACHES OF THE NORTHERN USVI. LOW RISK
ELSEWHERE. BY TOMORROW, THE MODERATE RISK WILL SPREAD TO NORTH-
FACING BEACHES OF AGUADA AND RINCON. BY SATURDAY, A NORTHERLY SWELL
IS FORECAST TO ARRIVE, INCREASING THE RISK TO HIGH FOR MOST BEACHES
IN NORTHERN PUERTO RICO, AND ALSO IN THE NORTHERN VIRGIN ISLANDS.
DANGEROUS BREAKING WAVES CAN BE EXPECTED AS WELL FOR THE WEEKEND AND
EARLY NEXT WEEK.
SJU WATCHES/WARNINGS/ADVISORIES
PR...EXTREME HEAT WARNING UNTIL 5 PM AST THIS AFTERNOON FOR
PRZ001>005-007-008-010-011.
HEAT ADVISORY UNTIL 5 PM AST THIS AFTERNOON FOR PRZ012-013.
VI...HEAT ADVISORY UNTIL 5 PM AST THIS AFTERNOON FOR VIZ001-002.
AM...NONE.
CVB/MRR
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