075
FXCA62 TJSJ 050816
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
416 AM AST MON MAY 5 2025
SYNOPSIS
A DRIER AIR MASS FILTERING OVER THE REGION WILL MAINTAIN CALM AND
STABLE WEATHER CONDITIONS THROUGH THE MORNING HOURS. LATER TODAY,
AFTERNOON CONVECTIVE WILL RETURN, ENHANCED BY TOPOGRAPHIC EFFECTS,
SEA BREEZES, AND DIURNAL HEATING, RESULTING IN PERIODS OF
MODERATE TO LOCALLY HEAVY RAIN DUE TO THUNDERSTORMS. A SHORT WAVE
TROUGH WILL REACH THE ISLANDS ON TUESDAY, INCREASING INSTABILITY
AND THE POTENTIAL TO OBSERVE HEAVY RAINFALL ONCE AGAIN. THERE IS
A LIMITED TO ELEVATED RISK OF FLOODING RAINS ACROSS THE ISLAND
EACH DAY.
SHORT TERM...TODAY THROUGH WEDNESDAY
A DRIER AIR MASS FILTERING OVER THE ISLANDS MAINLY RESULTED IN CLEAR
SKIES ACROSS PUERTO RICO AND THE US VIRGIN ISLANDS. GOES-19 INFRARED
CHANNEL AND THE DOPPLER RADAR OBSERVED SOME CLOUDS AND SHOWERS,
RESPECTIVELY, MAINLY ACROSS THE CARIBBEAN WATERS OVERNIGHT. ONCE
AGAIN, LOW TEMPERATURES DUG INTO THE LOW 60S ALONG MOUNTAINS AND
VALLEYS AS THE CLEAR SKIES ENHANCED NIGHTTIME COOLING. WINDS WERE
CALM TO LIGHT AND VARIABLE, INFLUENCED BY LAND BREEZE.
THIS MORNING, WE EXPECT CALM CONDITIONS, ALLOWING THE TEMPERATURE TO
REACH THE UPPER 80S OR EVEN THE LOW 90S, ESPECIALLY ALONG URBAN
AREAS OR COASTAL LOCATIONS. THESE AIR TEMPERATURES, COMBINED WITH
THE AVAILABLE MOISTURE, WILL PROMOTE THE RETURN OF WARM HEAT
INDICES, ESPECIALLY DURING THE MAXIMUM HEATING TIME NEAR NOON.
HOWEVER, THE SEASONAL AFTERNOON CONVECTION WILL RETURN, ENHANCED BY
LOCAL MOUNTAINS, SEA BREEZES, AND DIURNAL HEATING, RESULTING IN
PERIODS OF MODERATE TO LOCALLY HEAVY RAIN DUE TO THUNDERSTORMS. THE
HIGHEST RAINFALL AMOUNTS ARE EXPECTED ACROSS THE INTERIOR SECTIONS
AND DOWNWIND FROM THE LUQUILLO MOUNTAIN RANGE, GIVING PLACE TO THE
SAN JUAN STREAMER. MODEL GUIDANCE GENERALLY SUGGESTS BETWEEN 1 AND 2
INCHES OF RAIN WITH LOCALLY HIGHER AMOUNTS, ESPECIALLY ALONG PR'S
INTERIOR PORTIONS. SINCE MID-APRIL, PR RECEIVED BETWEEN 10 AND 20
INCHES OF RAIN ALONG THE INTERIOR SECTIONS, SATURATING THE SOILS AND
PRODUCING ABOVE-NORMAL RIVER LEVELS. THUS, PR HAS AN ELEVATED THREAT
OF FLOODING, AS MANY LOCATIONS IN THE INTERIOR AND NEAR MOUNTAINS
ARE VULNERABLE. SHOWERS WILL MOVE INLAND OVER THE US VIRGIN ISLANDS
FROM MID-MORNING ONWARD AS ADDITIONAL MOISTURE WILL BE LIFTED FROM
THE CARIBBEAN, ESPECIALLY ACROSS ST CROIX.
A SHORT WAVE TROUGH ALOFT WILL SWING BY THE ISLANDS ON TUESDAY, AND
A VERTICAL TRANSECT SHOWS DEEPER MOISTURE POOLING OVER THE ISLANDS
BY THE PEAK OF THE DIURNAL HEATING, WHICH COULD ASSIST IN THE
FORMATION OF SHOWERS ONE MORE TIME BY TUESDAY AFTERNOON. ALSO, AS
WINDS RETURN FROM THE NORTHEAST DURING THE EVENING, THEY WILL
INCREASE THE INTERACTION WITH THE LAND BREEZE, PROMOTING LATE
EVENING ACTIVITY ALONG THE ATLANTIC COASTLINE OF PR. THE AFTERNOON
AND EVENING ACTIVITIES WILL CREATE A LIMITED TO ELEVATED RISK OF
FLOODING RAINS ACROSS THE ISLANDS. AS THE MID TO UPPER-LEVEL TROUGH
AMPLIFIES OVER THE NORTHEAST CARIBBEAN, INSTABILITY WILL INCREASE
THE POTENTIAL TO OBSERVE DEEP CONVECTION. THE LIMITING FACTOR WE SEE
IN THE MODEL GUIDANCE IS THE MOISTURE EROSION THEY SUGGESTED.
HOWEVER, WE WILL CONTINUE TO MONITOR THE EVOLUTION OF THE WEATHER
CONDITIONS AS WE EXPECT THE AFTERNOON AND EVENING CONVECTION TO
DEVELOP EACH DAY.
LONG TERM...THURSDAY THROUGH MONDAY
A STRONG SURFACE HIGH PRESSURE LOCATED OVER THE CENTRAL TOWARD THE
NORTHEASTERN ATLANTIC WILL PROMOTE EAST TO SOUTHEASTERLY WINDS
THROUGHOUT THE FORECAST PERIOD. WINDS WILL BECOME FROM THE EAST ON
SUNDAY, AS ANOTHER SURFACE HIGH BUILDS OVER THE WESTERN ATLANTIC AND
MOVES TOWARD THE CENTRAL ATLANTIC. A MID-LEVEL RIDGE IS EXPECTED TO
BUILD OVER THE REGION, PROMOTING RELATIVELY DRIER CONDITIONS AND
STABILITY ALOFT. THE LATEST PRECIPITABLE WATER CONTENT HAS NEAR
NORMAL CLIMATOLOGICAL VALUES FROM 1.4 TO 1.6 INCHES. UNDER THIS
PATTERN, LIMITED RAINFALL ACTIVITY IS EXPECTED OVER THE AREA.
HOWEVER, AFTERNOON SHOWERS ARE POSSIBLE OVER PORTIONS OF THE
INTERIOR, WESTERN AND NORTHERN PUERTO RICO WITH ISOLATED
THUNDERSTORMS DUE TO THE COMBINATION OF DAYTIME HEATING AND
TOPOGRAPHIC EFFECT. BY THE END NEXT WEEKEND, A WIND SURGE COULD
POTENTIALLY REACHED THE AREA, INCREASING ONCE AGAIN THE LIKELIHOOD
TO OBSERVE SHOWERS SHOWERS AND ISOLATED THUNDERSTORMS OVER THE
ISLAND. THE 925 MB TEMPERATURES WILL REMAIN AT NORMAL
CLIMATOLOGICAL VALUES FOR THIS TIME OF THE YEAR, WITH TEMPERATURES
IN THE MID 80S ALONG THE COASTAL AND URBAN AREAS; AND FROM THE
MID TO UPPER 70S IN THE MOUNTAINS. ACROSS THE U.S. VIRGIN ISLANDS,
MAINLY FAIR WEATHER CONDITIONS WILL PREVAIL WITH LIMITED OR NONE
PRECIPITATION.
AVIATION
(06Z TAFS)
VFR CONDITIONS WILL PERSIST THIS MORNING. HOWEVER, SHRA/TSRA WILL
DEVELOP NEAR ISX AROUND NOON AND ACROSS THE INTERIOR SECTIONS OF PR,
IMPACTING JSJ/JBQ AND THE VCTY OF JPS. THIS ACTIVITY WILL MAINLY
FORM BETWEEN 5/15-22Z, WHEN MVFR CONDITIONS ARE LIKELY, IF IT MOVES
OVER THOSE TERMINALS. THE WINDS WILL BE CALM TO LIGHT AND VRB THRU
5/13Z, THEN INCREASING AT 9-13 KT FROM THE E-ESE WITH SEA BREEZE
VARIATIONS.
MARINE
A BROAD SURFACE HIGH PRESSURE EXTENDING FROM THE WESTERN INTO THE
CENTRAL ATLANTIC, IN COMBINATION WITH AN INDUCED SURFACE TROUGH JUST
NORTHEAST OF THE REGION, WILL RESULT IN LIGHT TO MODERATE EASTERLY
WINDS ACROSS THE LOCAL WATERS. MARINERS CAN EXPECT SEAS BETWEEN 3 TO
5 FEET FOR THE NEXT SEVERAL DAYS. THUNDERSTORMS ARE LIKELY TODAY
ACROSS THE REGIONAL WATERS, RESULTING IN HIGHER SEAS WITH THE
STRONGEST ACTIVITY.
BEACH FORECAST
THERE IS A MODERATE RISK OF RIP CURRENTS FOR THE BEACHES OF PUERTO
RICO FROM AGUADILLA TO FAJARDO. BEACHGOERS MUST EXERCISE CAUTION
DUE TO POSSIBLE LIFE- THREATENING RIP CURRENTS ALONG THE SURF ZONE
AND STAY WEATHER ALERT. THE RIP CURRENT RISK IS STILL EXPECTED TO
GRADUALLY DECREASE BY TUESDAY THROUGH THE REST OF THE WEEK.
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM...CAM
LONG TERM....GRS
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