A moist and ustable atmosphere combined with daytime heating and sea breeze convergence to produce scattered showers with thunderstorms over the municipality of Juana Diaz.
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The episode as NWS SJU wrote it up.
A moist and ustable atmosphere combined with daytime heating and sea breeze convergence to produce scattered showers with thunderstorms over the municipality of Juana Diaz.
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 27, 1:30 PM AST, 2 hours 24 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN JUAN PR ISSUED BY NATIONAL WEATHER SERVICE MIAMI FL 130 PM AST THU SEP 27 2012 .AVIATION...VFR WILL PREVAIL. HOWEVER, SHRA/TSRA NOW DEVELOPING OVER THE WESTERN INTERIOR COULD AFFECT TJMZ OVER THE NEXT FEW HOURS SO PLACED A TEMPO OF MVFR CIG/VIS THERE IN TSRA THROUGH 21Z. TSRA IS NEAR TJSJ SO PLACED VCTS THERE THROUGH THE REST OF THE AFTERNOON. ACROSS THE REST OF THE TERMINALS WILL CONTINUE WITH VFR, ALTHOUGH BRIEF MVFR IS POSSIBLE IN A PASSING SHOWER. HOWEVER, VCSH IS SUFFICIENT IN THE TAFS AT THIS TIME. ONSHORE WINDS WILL BECOME LIGHT/VARIABLE MOST LOCALES OVERNIGHT BEFORE BECOMING ONSHORE AGAIN MID MORNING ON FRIDAY. /GREGORIA && .PREV DISCUSSION... /ISSUED ISSUED BY NATIONAL WEATHER SERVICE MIAMI FL/ UPDATE...NO CHANGES TO THE FORECAST ARE REQUIRED THIS MORNING. THE MORNING SAN JUAN SOUNDING SHOWED AN UNSTABLE ATMOSPHERE WITH A PWAT OF 2.17 INCHES...NEARLY SATURATED UP THROUGH 15K FT THEN DRIER ABOVE THIS...AND THIS IS EVIDENT IN WATER VAPOR IMAGERY. THE 500 MB TEMP IS FAIRLY WARM AT -5.7C...BUT EVEN SO CAPE IS AROUND 3500 J/KG AND LI IS -5C...SO IT IS UNSTABLE. THUS, AS SEA BREEZE CONVERGENCE TAKES PLACES AND MAXIMIZES OVER THE WESTERN- SOUTHWESTERN INTERIOR THIS AFTERNOON, EXPECT DEVELOPING SHOWERS AND TSTORMS TO DEVELOP. THE PREVAILING LOW TO MID LEVEL WIND FLOW IS NE AT 9 KT...SO LIKE THE INHERITED HIGHEST POPS ACROSS THE WEST-SOUTHWEST PORTIONS OF PUERTO RICO. FOR EASTERN AREAS INCLUDING THE U.S. VIRGIN ISLANDS, EXPECT CONTINUED SCATTERED PASSING SHOWERS FROM TIME TO TIME WITH A SLIGHT CHANCE OF A THUNDERSTORM. MAIN CONCERN WITH AFTERNOON CONVECTION OVER INTERIOR/WESTERN PUERTO RICO WILL BE LOCALIZED HEAVY RAINS/POSSIBLE LOCALIZED FLOODING AS THE ATMOSPHERE IS MOIST BUT WITH WEAK LAPSE RATES (LIKELY PREVENTING STRONG STORMS FROM DEVELOPING). /GREGORIA PREV DISCUSSION... /ISSUED 608 AM AST THU SEP 27 2012/ SYNOPSIS...COMPUTER MODEL GUIDANCE DEPICTED TWO WEAK TUTT LOWS... ONE ACROSS THE CENTRAL CARIBBEAN JUST OVER CUBA AND ANOTHER ONE NORTHEAST OF THE REGION. BOTH SYSTEMS ARE EXPECTED TO FILL RAPIDLY TODAY AS AN UPPER LEVEL RIDGE BUILDS AND EXTENDS ACROSS THE LOCAL AREA FOR THE NEXT SEVERAL DAYS. A RELATIVELY UNSTABLE WEATHER PATTERN WILL PREVAIL ACROSS THE REGION UNTIL AT LEAST FRIDAY. DISCUSSION...VARIABLY CLOUDY SKIES PREVAILED ACROSS PUERTO RICO OVERNIGHT AND EARLY THIS MORNING. SCATTERED TO NUMEROUS SHOWERS AND A FEW THUNDERSTORMS DOTED THE ATLANTIC AND CARIBBEAN COASTAL WATERS OVERNIGHT AND EARLY THIS MORNING...WITH FEW OF THEM AFFECTING THE NORTHERN AND EASTERN SECTIONS OF PUERTO RICO FROM TIME TO TIME. SOME PERIODS OF MODERATE RAINFALL WAS OBSERVED ACROSS THE NORTHEASTERN AND EASTERN SECTIONS OF THE ISLAND. A COUPLE VERY WEAK TUTT LOWS...ONE ACROSS CENTRAL CARIBBEAN AND ANOTHER ONE NORTHEAST OF PUERTO RICO WILL CONTINUE TO FILL AS AN UPPER LEVEL RIDGE BUILDS ACROSS THE REGION TODAY AND FOR THE NEXT SEVERAL DAYS. HOWEVER...DEEP MOISTURE IN COMBINATION WITH AN UNSTABLE ATMOSPHERE...LOCAL EFFECTS AND UPPER LEVEL VENTILATION ASSOCIATED WITH THE AFOREMENTIONED DEVELOPING UPPER LEVEL RIDGE...WILL YIELD A FEW MORE DAYS OF FAIRLY ACTIVE WEATHER ACROSS THE LOCAL AREA...WITH SHOWERS AND THUNDERSTORMS MAINLY OVER THE SOUTH PART OF PUERTO RICO TODAY...THEN ACROSS THE NORTH COAST ON FRIDAY AND SATURDAY UNDER THE INFLUENCE OF A SOUTHEAST LOW TO MID LEVEL FLOW. AN OVERALL DRIER...MORE STABLE AND "WARMER" AIR MASS IS GENERALLY EXPECTED FOR SATURDAY...SUNDAY AND MONDAY. AVIATION...VFR CONDS ARE EXPECTED TO PREVAIL ACROSS ALL TAF SITES OVERNIGHT. HOWEVER...SCT -SHRA EMBEDDED IN THE LLVL NELY FLOW MAY AFFECT TIST...TISX AND TJSJ FM TIME TO TIME. AFTERNOON CONVECTION WILL DEVELOP ONCE AGAIN TOMORROW ACROSS CENTRAL...SOUTH AND WESTERN PR. AS A RESULT...EXPECT MOUNTAIN OBSCURATION AND PERIODS OF MVFR/IFR CONDS NEAR TJMZ AND TJPS BTWN 27/17 AND 27/21Z. EVENING TJSJ RAOB SHOWED MAINLY NE WINDS AT 10 KTS OR LESS BLW 20 KFT. && .PRELIMINARY POINT TEMPS/POPS... SJU 88 78 89 78 / 60 30 30 0 STT 86 79 86 79 / 50 30 30 30 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...NONE. VI...NONE. COASTAL WATERS...NONE. &&
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SAN JUAN PR 456 AM AST THU SEP 27 2012 AMZ710>745-PRZ001>013-280900- 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- 456 AM AST THU SEP 27 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO AND THE ADJACENT ATLANTIC COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT...ISOLATED THUNDERSTORMS WILL DEVELOP ACROSS PARTS OF THE INTERIOR AND WEST TO SOUTHWEST SECTIONS OF THE ISLAND DURING THE AFTERNOON. SOME STORMS WILL PRODUCE DANGEROUS CLOUD TO GROUND LIGHTNING...AND AREAS OF LOCALLY HEAVY RAINFALL WHICH MAY LEAD TO MINOR FLOODING OF SMALL RIVERS AND STREAMS. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED. AMZ715-725-VIZ001-002-280900- ST. THOMAS ST. JOHN ADJACENT ISLANDS-ST CROIX- NEARSHORE ATLANTIC AND ADJACENT CARIBBEAN COASTAL WATERS- 456 AM AST THU SEP 27 2012 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 AT THIS TIME. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION WILL NOT BE NEEDED.
The national radar mosaic for the moment the first event began.
1 flood. Local standard time, as filed.
Tomas Carrion Maduro urbanization was reported flooded.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Puerto Rico in 2012Every state in 2012This day in weather historyWarnings in Puerto Rico, September 2012
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: 414922.