A very moist southeast wind flow combined with strong upper level winds and daytime heating to produce numerous showers over the municipality of Guaynabo. This led to flash flooding affecting several families, roads and local business centers.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS SJU wrote it up.
A very moist southeast wind flow combined with strong upper level winds and daytime heating to produce numerous showers over the municipality of Guaynabo. This led to flash flooding affecting several families, roads and local business centers. Radar estimates indicated over 4 inches of rainfall were observed around or over the municipality of Guaynabo during this event. Structural damages, as well as loss of office supplies including computers, photocopies, surgery equipments, drugs and six cars were also damages. Property damage was estimated at more than $60,000.
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 May 18, 3:19 PM AST, 41 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN JUAN PR 319 PM AST FRI MAY 18 2012 .SYNOPSIS...BROAD AND ELONGATED MID TO UPPER LEVEL RIDGE EXTENDING NORTH NORTHEAST ACROSS THE REGION INTO THE WEST CENTRAL ATLANTIC... WILL CONTINUE TO BUILD AND SPREAD FURTHER NORTHEAST ACROSS NORTHERN LEEWARDS THROUGH SUNDAY. IN THE MEANTIME...THE UPPER LONG WAVE TROUGH WITH AXIS NOW JUST EAST OF THE LESSER ANTILLES WILL SHIFT FURTHER EASTWARD INTO THE TROPICAL ATLANTIC OVER THE WEEKEND. THIS WILL ALLOW FOR A PREVAILING NORTHERLY WIND FLOW WITH AN INCREASING SUBSIDENT PATTERN IN THE MID TO UPPER LEVELS. STRONG SURFACE HIGH PRESSURE ANCHORED ACROSS THE NORTH CENTRAL ATLANTIC AND EXTENDING SOUTHEAST ACROSS THE NORTHERN LEEWARDS...WILL BUILD FURTHER SOUTH INTO THE NORTHEASTERN CARIBBEAN OVER THE NEXT SEVERAL DAYS. THIS WILL MAINTAIN A FAIRLY TIGHT PRESSURE GRADIENT ACROSS THE REGION AND THEREBY INDUCE MODERATE TO STRONG EASTERLY TRADE WINDS. THE PREVAILING SOUTHEAST LOW LEVEL WIND FLOW WILL HOWEVER BECOME MORE EASTERLY BY LATE SUNDAY AND INTO EARLY NEXT WEEK AS THE ATLANTIC HIGH SINKS SOUTHWARDS. && .DISCUSSION...AT LEAST FOR THE NEXT 24 TO 48 HOURS...THE MOIST SOUTHEASTERLY LOW LEVEL WINDS WILL CONTINUE TO INFLUENCE CONVECTIVE DEVELOPMENT ACROSS THE ISLANDS AND COASTAL WATERS. FAIRLY TIGHT PRESSURE GRADIENT WILL ALSO MAINTAIN A MODERATE TO STRONG TRADE WIND FLOW ACROSS THE REGION. THE SHOWERS AND ISOLATED THUNDERSTORMS THAT DO DEVELOP ACROSS THE ISLANDS AND COASTAL WATERS WILL QUICKLY STREAM ACROSS THE ISLANDS...SO NO WIDESPREAD FLOODING IS ANTICIPATED AT THIS TIME. HOWEVER...AREA OF LOCALLY HEAVY DOWNPOURS WILL REMAIN LIKELY ESPECIALLY DURING THE EARLY MORNING HOURS ON THE EAST AND SOUTHEAST COASTAL SECTIONS OF PUERTO RICO...FOLLOWED BY LOCALLY INDUCED CONVECTIVE DEVELOPMENT ESPECIALLY ACROSS THE WEST AND NORTHWEST SECTIONS OF THE ISLANDS DURING THE AFTERNOONS. OVERALL MODELS SUGGEST A GRADUAL DECREASE IN PWAT VALUES ACROSS THE REGION AS TRADE WINDS BECOME MORE EASTERLY AND INCREASE BY EARLY NEXT WEEK. IN ADDITION...AS PREVIOUSLY MENTIONED MODELS SUGGEST INCREASE IN MID TO UPPER LEVEL SUBSIDENCE WITH MODERATE CAP NEAR 700 MILLIBARS BY SUNDAY AND INTO NEXT WEEK. THEREFORE...A GRADUAL DRYING IS STILL EXPECTED BY SUNDAY AND INTO THE EARLY PART OF NEXT WEEK WITH LESSER CONVECTIVE ACTIVITY ACROSS THE ISLANDS EXCEPT FOR LOCALLY AND DIURNALLY INDUCED CONVECTION EACH DAY IN ISOLATED AREAS. && .AVIATION...AFTERNOON CONVECTION WILL CONTINUE TO AFFECT PARTS OF THE FORECAST AREA THROUGH AT LEAST 18/23Z. THIS MAY RESULT IN MVFR/IFR CONDS IN AND AROUND TJBQ...TJSJ...TISX AND TNCM. IN ADDITION...MOUNTAIN OBSCURATION ARE LIKELY ALONG THE CORDILLERA CENTRAL. ELSEWHERE...VFR CONDS WITH A FEW PASSING SHOWERS ARE EXPECTED THROUGH THE FORECAST PERIOD. LLVL WINDS WILL BE MAINLY FROM THE SOUTHEAST AT 10 TO 20 KTS THROUGH THE END OF THE WEEK. && .PRELIMINARY POINT TEMPS/POPS... SJU 77 86 77 87 / 30 30 20 30 STT 77 87 78 88 / 30 30 20 40 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...NONE. VI...NONE. COASTAL WATERS...NONE. && 11/09
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SAN JUAN PR 621 AM AST FRI MAY 18 2012 AMZ710>745-PRZ001>013-191030- 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- 621 AM AST FRI MAY 18 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO AND THE ADJACENT ATLANTIC COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT SHOWERS AND THUNDERSTORMS WILL GROW OVER THE INTERIOR AND NORTHWEST QUADRANT OF PUERTO RICO CAUSING LOCAL URBAN AND SMALL STREAM FLOODING. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY SHOWERS AND THUNDERSTORMS WILL CONTINUE ACROSS THE AREA THROUGH AT LEAST SATURDAY AND THEN DECREASE SUNDAY AND MONDAY. LOCAL URBAN AND SMALL STREAM FLOODING WILL BE POSSIBLE AT LEAST THROUGH THEN. .SPOTTER INFORMATION STATEMENT... AMZ715-725-VIZ001-002-191030- ST. THOMAS ST. JOHN ADJACENT ISLANDS-ST CROIX- NEARSHORE ATLANTIC AND ADJACENT CARIBBEAN COASTAL WATERS- 621 AM AST FRI MAY 18 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE U.S. VIRGIN ISLANDS AND THE ADJACENT COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT SHOWERS WILL OCCUR FROM TIME TO TIME...SOME MAY BRING LOCALLY HEAVY RAINFALL...PRODUCING MINOR URBAN AND GUT FLOODING. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY WET CONDITIONS WILL CONTINUE FRIDAY AND SATURDAY...TAPERING OFF SUNDAY AND MONDAY. LOCAL URBAN AND GUT FLOODING WILL BE POSSIBLE AT LEAST FRIDAY AND SATURDAY. .SPOTTER INFORMATION STATEMENT...
The San Juan radar (TJUA), 28 km away, was scanning. The volume nearest the first event began at 19:59 UTC.
3 flash flood, 2 debris flow. Local standard time, as filed.
A total of 50 residents of California street in the Mallorca Urbanization were removed from their homes and taken to Centro de Envejecientes de Mu oz Rivera as a shelter.
San Patricio Avenue, San Jose street near San Francisco condominium, Los Filtros avenue and Altamira avenue were all flooded and impassable.
The Humane Society de Puerto Rico was completely flooded. Extensive damage were reported in the first floor of the building due to mud and flooding waters.
Mountain rock slide near Urbanization Villa Espana caused by heavy rainfall in the municipality of Guaynabo.
Landslide on Road PR-173 at the intersection of Route 1 caused by heavy rainfall was reported in Bayamon.
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, May 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: 384865, 384866, 384869, 384867, 384868.