A mid to upper level trough combined with a surface trough over the region and ample low level moisture to produce scattered to numerous showers with thunderstorms over Puerto Rico, affecting mainly the eastern half of the island.
Every event with a place to put it. Tap one for its entry below.
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 mid to upper level trough combined with a surface trough over the region and ample low level moisture to produce scattered to numerous showers with thunderstorms over Puerto Rico, affecting mainly the eastern half of the island.
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 10, 5:09 AM AST, 3 hours 1 minute earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN JUAN PR 509 AM AST THU MAY 10 2012 .SYNOPSIS...AMPLIFIED MID TO UPPER LEVEL TROUGH EXTENDING FROM THE SOUTHWEST ATLANTIC INTO THE CENTRAL CARIBBEAN...WILL CONTINUE TO LIFT EAST NORTHEAST ACROSS THE NORTHEASTERN CARIBBEAN TODAY THROUGH FRIDAY WHILE SLOWLY WEAKENING. IN THE MEANTIME...SHORT WAVE PERTURBATIONS WILL MOVE THROUGH THE BASE OF THE TROUGH AND CROSS THE LOCAL AREA OVER THE NEXT 24 TO 36 HOURS. AN ACCOMPANYING JET MAXIMA BETWEEN 65 TO 70 KNOTS WILL MOVE THROUGH REGION TODAY AS THE TROUGH SHIFTS EAST NORTHEAST. THIS PATTERN WILL FIRST INDUCE A SOUTHWESTERLY UPPER LEVEL FLOW THEN BECOME MORE NORTHWESTERLY OVER THE WEEKEND...AS RIDGE ALOFT BUILDS WEST OF THE REGION. STRONGEST DIVERGENCE NOW FOCUSED BETWEEN PUERTO RICO AND THE VIRGIN ISLANDS. THIS ALONG WITH GOOD THERMAL TROUGHING IN UPPER LEVEL WILL HELP CREATE VERY UNSTABLE CONDITIONS ACROSS THE REGION TODAY AND POSSIBLY THROUGH FRIDAY. IN THE LOW LEVELS...WEAK HIGH PRESSURE RIDGING ACROSS THE WEST CENTRAL ATLANTIC AND BROAD SURFACE TROUGH ACROSS THE EASTERN CARIBBEAN WILL MAINTAIN A MOIST SOUTHEASTERLY TRADE WIND FLOW ACROSS THE REGION OVER THE NEXT FEW DAYS AND INTO THE UPCOMING WEEKEND. MODEL GUIDANCE SUGGEST PWAT VALUES TO MAXIMIZE TO NEAR 2.0 INCHES OR SO TODAY THROUGH FRIDAY. && .DISCUSSION...FAVORABLE MID TO UPPER LEVEL CONDITIONS AND THE DEEP LAYERED MOISTURE TO BE INJECTED INTO THE FORECAST AREA TODAY AND ON FRIDAY...COMBINED WITH DIURNAL EFFECTS AND LOCAL FORCING WILL BE MORE THAN ENOUGH TO PRODUCE VERY UNSETTLED WEATHER CONDITIONS TODAY AND POSSIBLY TO A LESSER DEGREE ON FRIDAY. WITH SOIL ALREADY SATURATED ACROSS MUCH OF PUERTO RICO AND FAIRLY SATURATED ACROSS PARTS OF THE VIRGIN ISLANDS FROM RECENT RAINS...ANY ENHANCED CONVECTION TODAY WILL LEAD TO URBAN AND FLASH FLOODING. IN ADDITION... THE POTENTIAL FOR MUDSLIDES AND EXCESSIVE DEBRIS FLOW WILL REMAIN HIGH ACROSS PARTS OF THE ISLANDS ESPECIALLY IN AREAS OF STEEP TERRAIN OVER PUERTO RICO. ON SATURDAY A GRADUAL IMPROVEMENT IS STILL EXPECTED...HOWEVER EXPECT SUFFICIENT MOISTURE TO LINGER ACROSS THE REGION FOR LOCALLY AND DIURNALLY INDUCED AFTERNOON CONVECTION. FORMATION AND AREAS TO BE AFFECTED BY THE SHOWER ACTIVITY ACROSS THE INTERIOR WILL BE DEPENDENT ON THE LOCAL STEERING FLOW...WHICH AT THIS TIME WILL BE MAINLY FROM THE SOUTH SOUTHEAST OVER THE NEXT FEW DAYS. BASED ON THE LATEST MODEL GUIDANCE EXPECT THE LOCAL AREA TO DRY OUT SOMEWHAT BY SUNDAY WITH LESSER SHOWER AND THUNDERSTORM FORMATION ACROSS THE ISLANDS. && .AVIATION...SHOWERS...THUNDERSTORMS AND LOWER CIGS ACROSS TISX AND TIST WILL CONTINUE TO WORK THEIR WAY WEST NORTHWEST TOWARD TJSJ BY 10/11Z. MTN OBSCURATIONS AND SOME PERIODS OF MVFR OR EVEN IFR CONDS WILL OCCUR ACROSS THE EASTERN HALF OF PR THRU 10/14Z AS SHOWERS MOVE INLAND FROM ESE. SHWRS AND TSTMS EXPECTED AFT 10/16Z OVER INTERIOR AND WESTERN PR PRODUCING PERIODS OF MVFR OR IFR ACROSS TJMZ AND TJBQ BY 10/17Z...LASTING UNTIL 10/22Z. TJSJ 10/00Z SOUNDING INDICATED A WIND FLOW OF 5-15 KT UP THRU 10 KFT...BECOMING WEST SOUTHWESTERLY AND STRONGER ALOFT. && .PRELIMINARY POINT TEMPS/POPS... SJU 88 77 87 77 / 60 50 30 20 STT 85 76 86 77 / 60 50 40 30 && .SJU WATCHES/WARNINGS/ADVISORIES... PR...NONE. VI...NONE. COASTAL WATERS...NONE. && 72/09
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE SAN JUAN PR 522 AM AST THU MAY 10 2012 AMZ710>745-PRZ001>013-110930- 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- 522 AM AST THU MAY 10 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO AND THE ADJACENT ATLANTIC COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT AN AREA OF SHOWERS AND THUNDERSTORMS ACROSS EASTERN SECTIONS OF PUERTO RICO THIS MORNING WILL CONTINUE TO PROPAGATE SLOWLY WEST NORTHWESTWARD THIS AFTERNOON. THIS MOISTURE IN COMBINATION WITH DAYTIME HEATING AND LOCAL ISLANDS EFFECTS WILL INDUCE THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS ACROSS THE INTERIOR AND WESTERN PUERTO RICO THIS AFTERNOON AND EVENING. PERIODS OF HEAVY RAINFALL AND SOME FLOODING ARE EXPECTED...WITH THE POTENTIAL FOR FLASH AND RIVER FLOODING AS WELL AS MUDSLIDES IN AREAS OF STEEP TERRAIN. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY INCREASING LOW LEVEL MOISTURE AND INSTABILITY ACROSS THE REGION OVER THE NEXT FEW DAYS WILL INDUCE AN ACTIVE WEATHER PATTERN ACROSS THE REGION...WITH ADDITIONAL SHOWERS AND THUNDERSTORMS AND THE POTENTIAL FOR HEAVY RAINFALL AND SOME FLOODING. .SPOTTER INFORMATION STATEMENT... ANY REPORTS OF RAINFALL GREATER THAN THREE INCHES OR FLASH FLOODING WOULD BE GREATLY APPRECIATED. AMZ715-725-VIZ001-002-110930- ST. THOMAS ST. JOHN ADJACENT ISLANDS-ST CROIX- NEARSHORE ATLANTIC AND ADJACENT CARIBBEAN COASTAL WATERS- 522 AM AST THU MAY 10 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE U.S. VIRGIN ISLANDS AND THE ADJACENT COASTAL WATERS. .DAY ONE...TODAY AND TONIGHT AN AREA OF SHOWERS AND THUNDERSTORMS ACROSS THE LOCAL ISLANDS THIS MORNING WILL CONTINUE TO PROPAGATE SLOWLY WEST NORTHWESTWARD DURING THE REST OF THE MORNING HOURS AND THIS AFTERNOON. THIS MOISTURE IN COMBINATION WITH DAYTIME HEATING AND LOCAL ISLANDS EFFECTS WILL INDUCE THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS ACROSS THE LOCAL ISLANDS THIS AFTERNOON AND EVENING. PERIODS OF HEAVY RAINFALL AND SOME FLOODING ARE EXPECTED. .DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY INCREASING LOW LEVEL MOISTURE AND INSTABILITY ACROSS THE REGION OVER THE NEXT FEW DAYS WILL INDUCE AN ACTIVE WEATHER PATTERN ACROSS THE REGION...WITH ADDITIONAL SHOWERS AND THUNDERSTORMS AND THE POTENTIAL FOR HEAVY RAINFALL AND SOME FLOODING. .SPOTTER INFORMATION STATEMENT... ANY REPORTS OF HEAVY RAINFALL WOULD BE GREATLY APPRECIATED.
The San Juan radar (TJUA), 51 km away, was scanning. The volume nearest the first event began at 12:09 UTC.
3 flash flood, 2 flood. Local standard time, as filed.
Highways PR-3 and PR-53 to and from Ceiba and Fajardo were completely flooded,including the frontage roads.
Highway 901 was impassable in front of Banco Popular.
Highway 901 at Camino Nuevo sector was reported impassable.
Highway PR-906 was reported flooded At Palmas del Mar resort.
Highway PR-53 with intersection with road PR 927 was reported impassable.
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: 384514, 384515, 384516, 384517, 384518.