Strong thunderstorms with heavy showers developed across the south central Atlantic and low pressure moved into the western Atlantic affecting the local area.
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The episode as NWS SJU wrote it up.
Strong thunderstorms with heavy showers developed across the south central Atlantic and low pressure moved into the western Atlantic affecting the local area.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS San Juan, PR wrote its last area forecast discussion before the first event at Sep 18, 2:38 PM AST, 1 hour 8 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN JUAN PR 238 PM AST FRI SEP 18 2015 .SYNOPSIS...AT UPPER LEVELS...THE WEAK LOW WEST OF THE AREA DRIFTED SOUTH OF HISPANIOLA. THE TUTT LOW TO THE NORTHEAST WILL APPROACH BUT IS NOT EXPECTED TO STRENGTHEN BEFORE IT PULLS BACK NORTH LATE NEXT WEEK. NORTHERLY FLOW WILL CONTINUE THROUGH THE PERIOD. AT MID LEVELS...THE UPPER LEVEL PATTERN IS WEAKLY REFLECTED AT MID LEVELS...ESPECIALLY THE TUTT LOW...HOWEVER ALL GRADIENTS AND WINDS ARE QUITE WEAK. MOISTURE AT MID LEVELS WILL END ON SUNDAY AND RETURN ONLY WEAKLY MONDAY THROUGH THE REST OF THE WEEK. AT LOWER LEVELS...WEAK GRADIENTS BECOME EVEN WEAKER AS HIGH PRESSURE TO THE NORTH RECEDES TO THE NORTHEAST CENTRAL ATLANTIC AND LOW PRESSURE MOVES INTO THE WESTERN ATLANTIC AND CONTINUES TO AFFECT THE AREA EVEN AFTER IT SPLITS. SOME LOW PRESSURE SYSTEM ARE ALSO SEEN NORTHEAST OF THE AREA AS A REFLECTION OF THE TUTT LOW. && .DISCUSSION...STRONG THUNDERSTORMS WITH HEAVY SHOWERS DEVELOPED ACROSS THE SOUTH CENTRAL TIER OF PUERTO RICO AND NOW ALSO EXTEND ACROSS THE CORDILLERA CENTRAL TOWARD AGUADA. FURTHER DEVELOPMENT IS EXPECTED WITH FREQUENT LIGHTNING. A BAND OF MOISTURE LAYING ACROSS PUERTO RICO SEPARATING MOIST AIR FROM DRIER AIR TO THE NORTH WILL LAY ACROSS THE AREA FOR ONE MORE DAY BEFORE THE DRIER AIR MOVES INTO PUERTO RICO. OVERALL MOISTURE WILL PEAK AGAIN ON WEDNESDAY ACCORDING TO THE GFS. LOWER LEVEL MOISTURE...HOWEVER...IS NOT SEEN LEAVING UNTIL LATE NEXT WEEK. WINDS ARE UNUSUALLY LIGHT AS SURFACE GRADIENTS ARE WEAK. LOW PRESSURE IS PERSISTING NORTHEAST OF THE AREA IN THE WESTERN TROPICAL ATLANTIC AND IS GROWING IN THE WESTERN ATLANTIC OF THE UNITED STATES EASTERN SEABOARD. THEREFORE EXPECT STRONG CONVECTION TO PERSIST TOMORROW...DIMINISH SATURDAY THROUGH MONDAY AS MOISTURE DIMINISHES AND THE LIFTED INDEX INCREASES...BUT SOME SHOWERS AND THUNDERSTORMS SHOULD STILL BE EXPECTED. MOISTURE AND LIFTED INDICES RETURN AFTER TUESDAY AND THIS WITH THE CONTINUED LIGHT WINDS SUGGESTS STRONG AFTERNOON THUNDERSTORMS AND HEAVY RAINS WILL RETURN TO PUERTO RICO. LITTLE ACTIVITY IS EXPECTED ACROSS THE U.S. VIRGIN ISLANDS ALTHOUGH STREAMERS FROM UPSTREAM ISLANDS COULD BRING SOME HEAVY RAINS FOR A LITTLE WHILE DURING THE AFTERNOONS. DUE TO THE UPPER LEVEL LOW AND SOME SHEAR IN THE AREA...TROPICAL DEPRESSIONS MOVING TOWARD THE AREA DURING THE NEXT 10 DAYS ARE ALL FORECAST TO MOVE NORTH BEFORE THEY CAN APPROACH THE AREA. TROPICAL WAVES ARE SEEN TO BE BLOCKED AS WELL. THEREFORE ALMOST ALL WEATHER DURING THE NEXT 10 DAYS WILL BE DUE TO LOCAL FORCING AND HEATING. && .AVIATION...VFR CONDITIONS EXPECTED ACROSS MOST OF THE TAF SITES...EXCEPT AT TJMZ AND TJPS WHERE SHRA/TSRA COULD PRODUCE MVFR CONDS THRU 22Z. MOUNTAIN OBSCURATIONS OVER CENTRAL AND WEST INTERIOR PR. LOW LEVEL WINDS WILL BE VARIABLE AT AROUND 10 KT FM SFC TO FL200. && .MARINE...WINDS AND SEAS REMAIN RELATIVELY GENTLE. NO SMALL CRAFT ADVISORIES ARE EXPECTED DURING THE NEXT 10 DAYS. && .PRELIMINARY POINT TEMPS/POPS... SJU 79 88 79 89 / 30 50 20 20 STT 80 87 80 88 / 40 20 20 20 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...NONE. VI...NONE. AM...NONE. && 11/12
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SAN JUAN PR 500 AM AST FRI SEP 18 2015 AMZ710>745-PRZ001>013-191100- SAN JUAN AND VICINITY-NORTHEAST-SOUTHEAST-EASTERN INTERIOR- NORTH CENTRAL-CENTRAL INTERIOR-PONCE AND VICINITY-NORTHWEST- WESTERN INTERIOR-MAYAGUEZ AND VICINITY-SOUTHWEST-CULEBRA-VIEQUES- THE NEARSHORE AND OFF SHORE ATLANTIC AND CARIBBEAN COASTAL WATERS- 500 AM AST FRI SEP 18 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO AND THE ADJACENT ATLANTIC COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT .THUNDERSTORMS...THERE IS A CHANCE OF THUNDERSTORMS WITH MODERATE TO HEAVY RAINFALL, BRIEF GUSTY WINDS, AND OCCASIONAL LIGHTNING THIS AFTERNOON MAINLY ACROSS THE INTERIOR AND WESTERN PUERTO RICO...BUT AREAS IN AND AROUND THE SAN JUAN METROPOLITAN AREA MAY ALSO OBSERVED ISOLATED THUNDERSTORMS. .FLOODING...MODERATE TO HEAVY RAIN COULD LEAD TO URBAN AND SMALL STREAM FLOODING. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY SIMILAR PATTERN IS EXPECTED FOR SATURDAY. THE AVAILABLE MOISTURE WILL COMBINE WITH THE LOCAL EFFECTS AND DIURNAL HEATING AND DEVELOP SHOWERS AND THUNDERSTORMS ACROSS PORTIONS OF PUERTO RICO WHICH COULD LEAD TO URBAN AND SMALL STREAM FLOODING. .SPOTTER INFORMATION STATEMENT... WIDESPREAD SPOTTER ACTIVATION IS NOT ANTICIPATED, HOWEVER INDIVIDUAL SPOTTER ARE ENCOURAGED TO REPORT FLOODING AND RAINFALL AMOUNTS TO THE NATIONAL WEATHER SERVICE IN SAN JUAN. AMZ715-725-VIZ001-002-191100- ST. THOMAS ST. JOHN ADJACENT ISLANDS-ST CROIX- NEARSHORE ATLANTIC AND ADJACENT CARIBBEAN COASTAL WATERS- 500 AM AST FRI SEP 18 2015 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE U.S. VIRGIN ISLANDS AND THE ADJACENT COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT NO HAZARDOUS WEATHER IS EXPECTED. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY NO HAZARDOUS WEATHER IS EXPECTED. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED.
SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE SAN JUAN PR
124 PM AST FRI SEP 18 2015
PRZ006-007-181830-
PONCE AND VICINITY-CENTRAL INTERIOR-
124 PM AST FRI SEP 18 2015
AT 120 PM AST...A STRONG THUNDERSTORM OVER VILLALBA...JUANA DIAZ...
COAMO AND PONCE WAS NEARLY STATIONARY. THIS STORM IS PRODUCING
TORRENTIAL RAINFALL AND FREQUENT LIGHTNING. ADDITIONAL THUNDERSTORMS
WILL DEVELOP OVER THIS AREA DURING THE NEXT FEW HOURS.
TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY
CAUSE LOCALIZED FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.
FREQUENT CLOUD TO GROUND LIGHTNING IS OCCURRING WITH THIS STORM.
LIGHTNING CAN STRIKE 15 MILES AWAY FROM A THUNDERSTORM. SEEK A SAFE
SHELTER INSIDE A BUILDING OR VEHICLE.
LAT...LON 1819 6627 1812 6624 1803 6633 1806 6668
1813 6668 1816 6665 1817 6665 1821 6663
TIME...MOT...LOC 1724Z 180DEG 0KT 1812 6641
ERThe national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Low lying areas in PR'2 from San German to Hormigueros were reported flooded.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2015Every state in 2015This day in weather historyWarnings in Puerto Rico, September 2015
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 602938.