847
FXCA62 TJSJ 180635
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
235 AM AST SUN OCT 18 2026
..NEW SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST
KEY MESSAGES
ISSUED AT 235 AM AST SUN OCT 18 2026
* SHOWERS AND THUNDERSTORMS MAY CAUSE LOCALIZED FLOODING TODAY
AND MONDAY. FLOODING AND LIGHTNING THREATS WILL DECREASE MIDWEEK
BEFORE INCREASING AGAIN LATE IN THE WORKWEEK AND THROUGH THE
WEEKEND.
* A LINGERING NORTHERLY SWELL WILL SUBSIDE TODAY, FOLLOWED BY A
STRONGER SWELL MONDAY NIGHT, BRINGING DANGEROUS RIP CURRENTS,
HIGHER SURF, AND HAZARDOUS SEAS, PEAKING TUESDAY.
* LIMITED HEAT IMPACTS WILL MAINLY AFFECT HEAT-SENSITIVE
INDIVIDUALS DURING THE LATE MORNING AND EARLY AFTERNOON EACH
DAY.
* ACROSS THE U.S. VIRGIN ISLANDS, RAINFALL IMPACTS WILL REMAIN
LIMITED THROUGH TUESDAY, FOLLOWED BY INCREASING SHOWERS AND
THUNDERSTORMS LATE IN THE WORKWEEK. MARINE AND BEACH CONDITIONS
WILL DETERIORATE MONDAY NIGHT.
SHORT TERM(TODAY THROUGH TUESDAY)
ISSUED AT 235 AM AST SUN OCT 18 2026
ISOLATED TO SCATTERED SHOWERS DEVELOPED OVER THE SURROUNDING
WATERS OVERNIGHT, WITH SOME MOVING INLAND AND PRODUCING MINIMAL
RAINFALL ACCUMULATIONS. THIS ACTIVITY SHOULD CONTINUE THROUGH THE
MORNING, PARTICULARLY ACROSS WINDWARD AREAS, AS PATCHES OF
MOISTURE MOVE ALONG THE PREVAILING EAST TO SOUTHEAST FLOW. ALOFT,
A NORTHWARD-SHIFTING MID-LEVEL RIDGE AND WEAKENING UPPER-LEVEL
HIGH, INFLUENCED BY A LINGERING DEEP-LAYER TROUGH NORTHEAST OF THE
REGION, WILL GRADUALLY REDUCE SUBSIDENCE. ALTHOUGH MID-LEVEL
MOISTURE REMAINS LIMITED, PERIODIC MOISTURE PULSES SHOULD
GRADUALLY IMPROVE MOISTURE AVAILABILITY THROUGH MONDAY. WITH
MARGINAL INSTABILITY AND PRECIPITABLE WATER VALUES GENERALLY NEAR
TO BELOW THE OCTOBER CLIMATOLOGICAL MEDIAN OF 1.9 INCHES, DAYTIME
HEATING, SEA BREEZE CONVERGENCE, AND TERRAIN EFFECTS WILL SUPPORT
AFTERNOON SHOWERS AND ISOLATED THUNDERSTORMS ACROSS INTERIOR AND
NORTHWESTERN PUERTO RICO. WEAK STEERING FLOW MAY FAVOR SLOW-MOVING
CONVECTION AND LOCALLY HEAVY RAINFALL.
BY MONDAY, FURTHER WEAKENING OF THE MID-LEVEL RIDGE AND IMPROVING
MOISTURE DEPTH WILL SUPPORT SOMEWHAT DEEPER AND POTENTIALLY MORE
PERSISTENT AFTERNOON CONVECTION. SHOWERS AND ISOLATED TO SCATTERED
THUNDERSTORMS WILL FAVOR INTERIOR AND WESTERN PUERTO RICO, WHERE
NWS AND ECMWF ENSEMBLE GUIDANCE HIGHLIGHT LOCALLY ENHANCED
RAINFALL. BY TUESDAY, SOUTHEASTERLY LOW-LEVEL WINDS AND
INCREASINGLY SOUTHERLY FLOW NEAR 700 MB MAY SHIFT AFTERNOON
ACTIVITY TOWARD NORTHERN PUERTO RICO, ALTHOUGH CONVECTIVE COVERAGE
AND INTENSITY MAY BECOME MORE LIMITED. A BRIEF REDUCTION IN
MOISTURE IS EXPECTED TUESDAY NIGHT. MEANWHILE, INCREASING LOW-
LEVEL TEMPERATURES WILL FAVOR A GRADUAL WARMING TREND,
PARTICULARLY ACROSS NORTHERN COASTAL AND URBAN AREAS. HEAT IMPACTS
SHOULD REMAIN LIMITED, MAINLY AFFECTING INDIVIDUALS EXTREMELY
SENSITIVE TO HEAT, ESPECIALLY DURING THE LATE MORNING AND EARLY
AFTERNOON BEFORE INCREASING CLOUD COVER AND SHOWERS PROVIDE
LOCALIZED RELIEF.
THE MAIN HAZARDS WILL BE LOCALLY HEAVY RAINFALL, LIGHTNING, AND
ISOLATED FLOODING, PARTICULARLY TODAY AND MONDAY. PONDING OF WATER
ON ROADS AND IN POORLY DRAINED AREAS IS LIKELY BENEATH HEAVIER
SHOWERS, WITH A LOW CHANCE OF URBAN AND SMALL-STREAM FLOODING.
ISOLATED FLASH FLOODING CANNOT BE RULED OUT WHERE SLOW-MOVING OR
REPEATEDLY DEVELOPING THUNDERSTORMS PRODUCE PROLONGED RAINFALL,
ESPECIALLY ACROSS INTERIOR AND WESTERN PUERTO RICO. MONDAY MAY
FAVOR DEEPER AND MORE PERSISTENT THUNDERSTORMS, WHILE TUESDAY'S
RAINFALL AND LIGHTNING THREATS SHOULD BECOME MORE LIMITED, WITH
ANY HEAVIER ACTIVITY POTENTIALLY SHIFTING TOWARD NORTHERN PUERTO
RICO.
LONG TERM(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 235 AM AST SUN OCT 18 2026
RELATIVELY DRIER CONDITIONS ON WEDNESDAY WILL TRANSITION INTO A
WETTER AND MORE UNSETTLED PATTERN THURSDAY THROUGH SUNDAY. THE
INTERACTION BETWEEN A SURFACE HIGH OVER THE CENTRAL ATLANTIC AND A
DEEP-LAYER LOW OVER THE EASTERN CONUS WILL MAINTAIN A GENERALLY
SOUTHEAST TO SOUTHERLY WIND FLOW ACROSS THE REGION, WITH STEERING
WINDS STRENGTHENING LATE THURSDAY INTO SATURDAY. WEDNESDAY
APPEARS TO BE THE DRIEST DAY OF THE PERIOD, AS MODEL GUIDANCE
SUGGESTS BELOW-NORMAL LOW- TO MID-LEVEL MOISTURE, WITH
PRECIPITABLE WATER VALUES BELOW 1.6 INCHES. NEVERTHELESS, DAYTIME
HEATING AND LOCAL EFFECTS MAY STILL SUPPORT AFTERNOON SHOWERS
ACROSS PORTIONS OF PUERTO RICO.
A CONSIDERABLE INCREASE IN MOISTURE IS EXPECTED BY THURSDAY AS
DEEP TROPICAL MOISTURE SPREADS ACROSS THE NORTHEASTERN CARIBBEAN.
MODEL GUIDANCE SUGGESTS PRECIPITABLE WATER VALUES EXCEEDING 2.0
INCHES THROUGH MUCH OF THE REMAINDER OF THE PERIOD, OCCASIONALLY
APPROACHING 2.4 INCHES, WITH PERIODS OF ABOVE-NORMAL MOISTURE.
INCREASING MID-LEVEL HUMIDITY, COOLING TEMPERATURES ALOFT, AND
THE PROXIMITY OF A DEEP-LAYER TROUGH WILL SUPPORT A MORE FAVORABLE
ENVIRONMENT FOR DEEPER CONVECTION. ALTHOUGH A MID-LEVEL RIDGE MAY
GRADUALLY BUILD OVER THE EASTERN CARIBBEAN, ABUNDANT MOISTURE AND
LOCAL EFFECTS SHOULD CONTINUE TO FAVOR SHOWERS AND THUNDERSTORMS.
AN ADVECTIVE SHOWER PATTERN IS EXPECTED ACROSS WINDWARD SECTIONS
OF THE ISLANDS, PARTICULARLY DURING THE NIGHTTIME AND MORNING
HOURS, FOLLOWED BY AFTERNOON CONVECTION ACROSS THE INTERIOR AND
WESTERN PORTIONS OF PUERTO RICO. INCREASING STEERING WINDS LATE
THURSDAY THROUGH SATURDAY SHOULD ALLOW CONVECTION TO BECOME MORE
PROGRESSIVE, ALTHOUGH LOCALLY HEAVY RAINFALL MAY STILL RESULT IN
URBAN AND SMALL-STREAM FLOODING, ISOLATED FLASH FLOODING, AND
RISES IN RIVER LEVELS. BY SUNDAY, STEERING WINDS MAY WEAKEN AGAIN,
POTENTIALLY FAVORING SLOWER-MOVING THUNDERSTORMS AND GREATER
LOCALIZED RAINFALL ACCUMULATIONS.
UNDER THE PREVAILING SOUTHEAST TO SOUTHERLY FLOW, WARMER THAN
NORMAL TEMPERATURES ARE LIKELY, PARTICULARLY ACROSS NORTHERN
COASTAL AND URBAN AREAS OF PUERTO RICO. COMBINED WITH ABUNDANT
MOISTURE, HEAT INDICES MAY EXCEED 100 DEGREES FAHRENHEIT, MAINLY
DURING THE LATE MORNING AND EARLY AFTERNOON. HEAT IMPACTS MAY
RANGE FROM LIMITED TO ELEVATED, PARTICULARLY FOR INDIVIDUALS
SENSITIVE TO HEAT, AND HEAT PRODUCTS MAY BE ISSUED IF CONDITIONS
WARRANT.
AVIATION
(06Z TAFS)
ISSUED AT 235 AM AST SUN OCT 18 2026
VFR CONDS EXPECTED TO PREVAIL ACROSS MOST TERMINALS THROUGH THE
TAF PRD. SCT -SHRA WILL CONTINUE ACROSS THE LOCAL WATERS THROUGH
THE MORNING, WITH BRIEF ACTIVITY AFFECTING TJSJ AND USVI TERMINALS
THROUGH 18/14Z. TEMPO MVFR CONDS POSSIBLE WITH REDUCED VIS/CIGS IN
HEAVIER SHRA. AFTN SHRA/TSRA EXPECTED ACROSS INTERIOR AND NW PR,
PARTICULARLY AFT 18/17Z, WITH VCTS POSSIBLE AT TJBQ AND
POTENTIALLY TJSJ. BRIEF MVFR OR LOCALLY IFR CONDS POSSIBLE BENEATH
HEAVIER CONVECTION, ALONG WITH MOUNTAIN OBSCURATIONS. E-ESE WINDS
AT 5-10 KT EARLY, INCREASING TO 8-12 KT AFT 18/13Z WITH SEA BREEZE
VARIATIONS.
MARINE
ISSUED AT 235 AM AST SUN OCT 18 2026
A WEAK PRESSURE GRADIENT WILL MAINTAIN GENTLE TO MODERATE EAST TO
SOUTHEAST WINDS ACROSS THE LOCAL WATERS THROUGH MIDWEEK.
RELATIVELY FAVORABLE MARINE CONDITIONS ARE EXPECTED TODAY INTO
MONDAY, BEFORE AN ENERGETIC, LONG-PERIOD NORTHWEST TO NORTH SWELL
BEGINS ARRIVING MONDAY EVENING. THE SWELL WILL PEAK TUESDAY,
BUILDING SEAS TO 5 TO 7 FEET, OCCASIONALLY UP TO 9 FEET, ACROSS
THE ATLANTIC WATERS, NORTHERN COASTAL WATERS, AND EXPOSED LOCAL
PASSAGES. HAZARDOUS CONDITIONS FOR SMALL CRAFT ARE POSSIBLE, WITH
ELEVATED SEAS GRADUALLY SUBSIDING LATER IN THE WEEK. MEANWHILE,
PASSING SHOWERS AND ISOLATED THUNDERSTORMS MAY PRODUCE LOCALLY
HAZARDOUS CONDITIONS, PARTICULARLY NEAR THE NORTHERN AND WESTERN
COASTAL WATERS DURING THE AFTERNOONS.
BEACH FORECAST
ISSUED AT 235 AM AST SUN OCT 18 2026
A MODERATE RISK OF RIP CURRENTS WILL CONTINUE TODAY INTO EARLY
MONDAY ALONG EXPOSED NORTHERN BEACHES OF PUERTO RICO AND MUCH OF
THE U.S. VIRGIN ISLANDS, INCLUDING EASTERN ST. CROIX. THE RISK
MAY INCREASE TO HIGH ALONG PORTIONS OF NORTHERN PUERTO RICO ON
MONDAY, AHEAD OF A MORE ENERGETIC, LONG-PERIOD NORTHWEST TO NORTH
SWELL ARRIVING MONDAY EVENING. THIS SWELL WILL BUILD THROUGH
TUESDAY, PRODUCING INCREASINGLY DANGEROUS RIP CURRENTS AND HIGHER
SURF ALONG EXPOSED BEACHES, WITH HAZARDOUS CONDITIONS POTENTIALLY
PERSISTING THROUGH MIDWEEK.
BREAKING WAVES ARE CURRENTLY FORECAST TO REACH 7 TO 8 FEET ALONG
PORTIONS OF NORTHERN PUERTO RICO. HOWEVER, LOCALIZED SURF OF 10
FEET OR HIGHER CANNOT BE RULED OUT AT THE MOST EXPOSED BEACHES,
POTENTIALLY REACHING HIGH SURF ADVISORY CRITERIA. ADDITIONALLY,
AFTERNOON THUNDERSTORMS MAY PRODUCE LIGHTNING AND LOCALLY GUSTY
WINDS NEAR BEACHES, PARTICULARLY TODAY AND MONDAY.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
DAY...CAM/MNG
EVE...MRR/RVM
MID...ICP
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