541
FXCA62 TJSJ 010825
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
425 AM AST SUN JUN 1 2025
UPDATE
* HAZY SKIES AND LIMITED SHOWER ACTIVITY WILL PERSIST TODAY DUE TO
THE PRESENCE OF SAHARAN DUST PARTICLES OVER THE ISLANDS.
* WARMER CONDITIONS WILL REMAIN IN PLACE DUE TO A SOUTHEASTERLY
WIND FLOW ACROSS THE ISLANDS. THEREFORE, A HEAT ADVISORY IS IN
EFFECT FOR MOST COASTAL AREAS OF PUERTO RICO FROM 10 AM TO 4 PM.
* IMPROVING WEATHER CONDITIONS ARE FORECAST FROM TUESDAY ONWARD.
SHORT TERM...TODAY THROUGH TUESDAY
HAZY SKIES LIMITED NIGHTTIME COOLING, RESULTING IN WARMER-THAN-
NORMAL MINIMUM TEMPERATURES ACROSS PUERTO RICO AND THE US VIRGIN
ISLANDS. OVERNIGHT LOW TEMPERATURES RANGED FROM THE MID-TO-UPPER 60S
IN THE MOUNTAIN REGIONS TO THE UPPER 70S OR EVEN THE LOW 80S ALONG
THE LOWER ELEVATIONS. THE DOPPLER RADAR DETECTED A FEW ISOLATED
SHOWERS BROUGHT BY THE EAST-SOUTHEASTERLY WIND, MOVING INLAND ACROSS
WINDWARD SECTIONS OF THE ISLANDS.
A RELATIVELY STABLE WEATHER PATTERN IS FORECAST FOR PUERTO RICO AND
THE US VIRGIN ISLANDS THROUGH TUESDAY, AS INDICATED BY MODEL
GUIDANCE. THIS PATTERN WILL BE CHARACTERIZED BY NEAR-TO-BELOW-NORMAL
MOISTURE CONTENT, A DENSE SAHARAN AIR LAYER (SAL), AND THE INFLUENCE
OF A MID-LEVEL HIGH PRESSURE. THE HIGH PRESSURE WILL PROMOTE A TRADE
WIND INVERSION, CAPPING CONVECTION AND LIMITING SIGNIFICANT VERTICAL
DEVELOPMENT OF CLOUDS. IN ADDITION, A DENSE CONCENTRATION OF
SUSPENDED DUST PARTICLES WILL PERSIST OVER THE REGION. THE SAL WILL
RESULT IN DEGRADED AIR QUALITY AND HAZY SKIES ACROSS THE ISLANDS.
THE SAL WILL ALSO CONTRIBUTE TO WARMER-THAN-NORMAL TEMPERATURES,
ESPECIALLY DURING NIGHTTIME HOURS, REDUCING RADIATIONAL COOLING AND
CONTRIBUTING TO HOTTER MINIMUM TEMPERATURES EACH MORNING.
WITH A SUPPRESSED CONVECTIVE ENVIRONMENT AND LIMITED INSTABILITY, WE
ANTICIPATE BRIEF AND FAST-MOVING SHOWERS, PRIMARILY ACROSS THE
WINDWARD AREAS OF PR AND THE USVI, DRIVEN BY A BREEZY EAST-SOUTHEAST
WIND FLOW. THESE SHOWERS MAY OCCASIONALLY MOVE INLAND DUE TO A LOW-
LEVEL WIND SURGE THAT ENHANCES MOISTURE ADVECTION. DURING THE
AFTERNOONS, LIMITED CONVECTIVE DEVELOPMENT IS EXPECTED ALONG WESTERN
PR AND DOWNWIND FROM THE USVI, ALTHOUGH WIDESPREAD RAINFALL IS NOT
ANTICIPATED. MODEL GUIDANCE SUPPORTS THIS OUTLOOK, SHOWING RELATIVE
STABILITY IN THE MID-LEVELS, WITH 500 MB TEMPERATURES NEAR NORMAL
AND A PRONOUNCED LAPSE RATE INVERSION LIMITING VERTICAL MIXING AND
THUNDERSTORM DEVELOPMENT.
HEAT-RELATED IMPACTS, HOWEVER, ARE OF INCREASING CONCERN. THE
COMBINATION OF PERSISTENT SAL, REDUCED OVERNIGHT COOLING, AND RISING
DAYTIME TEMPERATURES WILL ELEVATE THE HEAT INDEX VALUES EACH
AFTERNOON. THE 925 MB TEMPERATURE MODEL GUIDANCE CONFIRMS HOTTER-
THAN-AVERAGE TEMPERATURES AT LOW LEVELS, SUGGESTING THAT HEAT
ADVISORIES OR EVEN EXCESSIVE HEAT WARNINGS MAY BE REQUIRED EACH DAY
BETWEEN 10 AM AND 4 PM, AT LEAST STARTING TODAY, SUNDAY. WHILE WE
EXPECT A GRADUAL DECREASE IN DUST CONCENTRATION BY TUESDAY
AFTERNOON, HAZY SKIES WILL LIKELY LINGER UNTIL A CLEANER AIR MASS
REPLACES THE SAL. RESIDENTS SHOULD REMAIN ALERT FOR UPDATES ON HEAT-
RELATED ADVISORIES AND TAKE PRECAUTIONS TO MITIGATE HEAT STRESS,
ESPECIALLY IN URBAN AND POORLY VENTILATED AREAS. INDIVIDUALS WITH
RESPIRATORY CONDITIONS, SUCH AS ASTHMA OR ALLERGIES, SHOULD FOLLOW
THEIR MEDICAL RECOMMENDATIONS AND USE PROTECTIVE MEASURES AS NEEDED.
LONG TERM...WEDNESDAY TROUGH SUNDAY
A BROAD SURFACE HIGH OVER THE CENTRAL ATLANTIC AND AN INDUCED
TROUGH NORTH OF THE WESTERN ATLANTIC WILL MAINTAIN AN EASTERLY
WIND FLOW ACROSS THE LOCAL ISLANDS ON WEDNESDAY. THIS PATTERN WILL
SUPPORT THE ADVECTION OF SHALLOW PATCHES OF MOISTURE, WITH
PRECIPITABLE WATER VALUES RANGING FROM 1.2 TO 1.7 INCHES. GLOBAL
MODEL GUIDANCE SUGGESTS LIMITED TO NO LINGERING SAHARAN AIR LAYER
(SAL) PRESENCE, RESULTING IN IMPROVED VISIBILITY AND REDUCED HAZE.
SUBSIDENCE ALOFT ASSOCIATED WITH A STRENGTHENING MID- TO UPPER-
LEVEL RIDGE WILL PROMOTE A STABLE ATMOSPHERE, SUPPRESSING DEEP
CONVECTION ACROSS MUCH OF THE REGION. HOWEVER, LOCALLY INDUCED
SHOWERS AND ISOLATED THUNDERSTORMS REMAIN POSSIBLE ACROSS WESTERN
PUERTO RICO DURING THE AFTERNOON DUE TO DIURNAL HEATING AND LOCAL
CONVERGENCE. FROM FRIDAY THROUGH SUNDAY, A GRADUAL SHIFT IN THE
LOW-LEVEL WIND FLOW TOWARD A MORE SOUTHERLY COMPONENT IS EXPECTED,
FAVORING WEAK WARM AIR ADVECTION. THIS WILL LIKELY RESULT IN
ELEVATED TEMPERATURES ACROSS THE NORTHERN COASTAL AND INTERIOR
SECTIONS OF PUERTO RICO, WITH WARMER CONDITIONS EXTENDING INTO THE
U.S. VIRGIN ISLANDS. UNDER MOSTLY SUNNY SKIES AND CONTINUED MID-
LEVEL SUBSIDENCE, HEAT INDICES COULD REACH OR EXCEED ADVISORY
THRESHOLDS. RESIDENTS ARE ENCOURAGED TO STAY HYDRATED AND FOLLOW
OFFICIAL HEAT SAFETY RECOMMENDATIONS DURING THIS PERIOD.
AVIATION
(06Z TAFS)
MAINLY VFR CONDITIONS ACROSS THE TERMINALS. A DENSE SAHARAN AIR
LAYER WILL LIMIT VISIBILITIES BETWEEN 5 AND 9 SM. ANY SHRA WILL BE
BRIEFED, WITH MINIMAL IMPACT ON OPERATIONS FOR MOST TERMINALS.
EXPECT WINDS FROM THE ESE TO RANGE AT 15-20 KTS AFTER 01/13Z, WITH
HIGHER GUSTS AROUND 25 KT OR MORE. ONCE AGAIN WE EXPECT WINDS TO
RANGE AT 10 KT OR LESS OVERNIGHT (AFTER 01/23Z). VCSH WILL DEVELOP
NEAR TJBQ DURING THE AFTERNOON HOURS, BUT WE ARE NOT ANTICIPATING
WIDESPREAD ACTIVITY.
MARINE
A BROAD SURFACE HIGH PRESSURE EXTENDING ACROSS THE ATLANTIC BASIN
WILL MAINTAIN A MODERATE TO LOCALLY FRESH EAST-SOUTHEASTERLY WIND
FLOW ACROSS THE LOCAL WATERS. AS A RESULT, SEAS WILL REMAIN UP TO
5 FEET, WITH LOCALLY HIGHER SEAS OF UP TO 6 FEET DUE TO WIND-
DRIVEN WAVES. SMALL CRAFT OPERATORS SHOULD EXERCISE CAUTION ACROSS
THE EXPOSED LOCAL WATERS TODAY AND THROUGH THE UPCOMING WORKWEEK.
INCREASING IN SURFACE WIND IS FORECAST AGAIN BY LATE TUESDAY INTO
WEDNESDAY, RESULTING IN WIND DRIVEN SEAS AGAIN.
BEACH FORECAST
THERE IS A MODERATE RISK OF RIP CURRENTS ALONG THE SOUTHERN
COASTAL AREAS, PARTICULARLY IN THE SOUTHWESTERN REGION, ST. CROIX,
CULEBRA, AND VIEQUES. THE RISK WILL INCREASE FOR THE REMAINING
SOUTHERN COASTAL AREAS TONIGHT. ON WEDNESDAY, THE MODERATE RISK OF
RIP CURRENTS WILL EXTEND ACROSS THE NORTHERN COAST OF PUERTO RICO
AND THE REST OF THE ISLANDS.
SJU WATCHES/WARNINGS/ADVISORIES
PR...HEAT ADVISORY FROM 10 AM THIS MORNING TO 5 PM AST THIS AFTERNOON
FOR PRZ001-003-005-007-008-010-011.
VI...NONE.
AM...NONE.
SHORT TERM & AVIATION...CAM
LONG TERM & MARINE....LIS
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