Flash Flood and Debris Flow in Puerto Rico, May 14 to 18, 2011

Name: Flash Flood and Debris Flow in Puerto Rico, May 14 to 18, 2011
Start: 2011-05-14T13:09
End: 2011-05-18T16:45
Location: Puerto Rico

May 14 to 18, 2011 · NWS SJU · 9 events in 7 counties and zones

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

The toll

Deaths: 0
Injuries: 0
Property damage: $365,000
Crop damage: None recorded
Events: 9

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.

What happened

The episode as NWS SJU wrote it up.

A broad trough associated with a persistent surface low north of the area and a wide northeast to southwest swath of moisture south of Puerto Rico moved very slowly east and created a highly unstable environment across the local area. This instability led to the development of very strong thunderstorms. The thunderstorms first affected the municipality of Trujillo Alto then eventually spread north and east towards the northeast sections of Puerto Rico, producing pea to marble size hail, and isolated cases of quarter size hail at Villas de Carraizo, and strong gusty winds between 40 and 60 mph across several municipalities. Many downed trees were reported at and near the Outlets Mall parking in Canovanas, a few vehicles were damaged, as the trees fell on top. Other municipalities of the northeast like Fajardo reported numerous downed trees, pea size hail, and some homes with partial zinc roof damage.

What forecasters said that day

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 14, 12:09 PM AST, 1 hour earlier.

Area forecast discussion, May 14, 12:09 PM AST, 1 hour before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1209 PM AST SAT MAY 14 2011

.UPDATE...THE 12Z SOUNDING SHOWED ALMOST IDENTICAL PRECIPITABLE
WATER FROM 12 HOURS PREVIOUS...BUT CONSIDERABLY MORE INSTABILITY.
SHOWERS SOUTHWEST OF PUERTO RICO HAVE MOVED ONSHORE AND THE
MOISTURE IS COMBINING WITH THE HEATING TO PRODUCE THUNDERSTORMS
WITH TOPS UP TO 40 KFT SO FAR.

&&

.DISCUSSION...WINDS ARE SOUTHWEST JUST ABOVE THE SURFACE AND ARE
GREATLY INFLUENCING THE MOVEMENT AND LOCATION OF FORMATION OF THE
SHOWERS. HAVE RAISED THE POPS IN SOME PARTS OF PUERTO RICO AS WELL
AS THE AMOUNT OF RAINFALL EXPECTED. SOUTHWEST JET OVERHEAD WILL
CONTRIBUTE TO GOOD VENTILATION OF THUNDERSTORMS. THIS IS
EXPECTED TO BE AN ACTIVE DAY WITH SOME URBAN AND SMALL STREAM
FLOODING AND RAPID RIVER RISES IN SOME PLACES. SHOWERS WILL LIKELY
CONTINUE TO MOVE TOWARD THE NORTHEAST AND FILL-IN OVER THE ISLAND.
THE U.S. VIRGIN ISLANDS MAY SEE SOME OF THIS ACTIVITY MUCH LATER
IN THE AFTERNOON...BUT HEAVY CLOUD COVER AND AND SOMEWHAT DRIER
AIR OVER THEM WILL KEEP SHOWER ACTIVITY DOWN FOR NOW.

&&

.AVIATION...WINDS ARE VARIABLE...WITH SOME STATIONS REPORTING SEA
BREEZES AND SOME NOT. SHOWERS AND THUNDERSTORMS MAY PRODUCE GUSTY
WINDS THEIR VICINITY. WINDS FROM 44-46 THOUSAND FEET WERE 100
KNOTS IN THE SOUNDING...AND RISING FROM LESS THAN 5 TO AROUND 35
KNOTS FROM 4 TO 30 KFT. SOME BRIEF MVFR CONDS MAY BE EXPECTED AT
ALL TAF SITES AND MOUNTAIN OBSCURATIONS IN PUERTO RICO THROUGH
15/18Z.

&&

.PREV DISCUSSION... /ISSUED 444 AM AST SAT MAY 14 2011/

SYNOPSIS...CUTOFF LOW NORTH OF BERMUDA WILL CONTINUE TO WEAKEN
OVER THE NEXT 12 TO 24 HRS. LOW AMPLITUDE SHORTWAVE TROF EXTENDING
FROM NORTH OF HISPANIOLA SOUTH INTO THE CARIBBEAN WILL MOVE ACROSS
PR/USVI TODAY. SUB-EQUATORIAL RIDGE ACROSS THE TROP ATLC WILL BUILD
WESTWARD INTO THE CARIBBEAN NEXT WEEK.

DISCUSSION...AFTER A QUITE NIGHT...SHOWERS AND THUNDERSTORMS ONCE
AGAIN BEGAN TO DEVELOP ACROSS THE EASTERN WATERS OF PUERTO RICO.
MOST OF THESE SHOWERS AND THUNDERSTORMS WERE STATIONARY BUT THEY
SPREAD NORTHEAST ACROSS THE LOCAL ISLANDS. THE HEAVIEST RAINFALL
AND STRONGEST THUNDERSTORMS REMAINED OVER WATERS.

THE INFLUX OF DEEP TROPICAL MOISTURE WILL CONTINUE TODAY AND MID
TO UPPER LEVEL CONDITIONS CONTINUE TO BE FAVORABLE FOR SHOWER AND
THUNDERSTORM DEVELOPMENT FOR THIS AFTERNOON CONVECTIVE ACTIVITY.
VARIABLE TO MOSTLY CLOUDY SKIES WILL PREVAIL THROUGH MID
MORNING...THIS WILL SLOW DOWN THE CONVECTIVE PROCESS FOR THIS
AFTERNOON. AFTER MID MORNING SKIES WILL BECOME MORE CLEAR THEREFORE
MORE SURFACE HEATING WILL OCCUR. THIS WILL IGNITE ONCE AGAIN THE
SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE EASTERN INTERIOR AND
NORTHEAST PORTIONS OF PUERTO RICO THIS AFTERNOON.

MUCH DRIER WEATHER SHOULD RETURN TO ALL ISLANDS BY SUNDAY...AS A
WEAK UPPER LEVEL RIDGE BUILDS NORTH OF THE ISLANDS. UNFORTUNATELY...THE
WETTER PATTERN RETURNS EARLY NEXT WEEK AS A SERIES OF SHORT WAVE
TROUGHS STREAM ACROSS THE ISLANDS.

AVIATION...TEMPO MVFR CONDS DUE TO LOW CIGS WITH SHRA/ISOLD TSRA
ACTIVITY ACROSS TJSJ...TIST AND TJNR BETWEEN 16Z AND 22Z. VCTS
POSSIBLE FOR TJSJ AND TIST. SFC WINDS WILL BE MOSTLY LIGHT FROM
THE SOUTH ACROSS MOST TERMINALS.

MARINE...ALTHOUGH THE BUOY 41043 CONTINUE TO REPORT A NORTHERN
SWELL 6.9 FEET...IT WILL BEGIN TO SLOWLY SUBSIDE THROUGH EARLY
MONDAY MORNING. MARINERS ACROSS THE WATERS EAST OF PUERTO RICO
SHOULD BE AWARE OF HEAVY SHOWERS AND THUNDERSTORMS THROUGH LATE
THIS AFTERNOON.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  88  74  86  75 /  60  20  50  20
STT  84  75  86  76 /  50  30  30  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
&&

12/23

Hazardous weather outlook, May 14, 4:21 AM AST, 8 hours 48 minutes before

HAZARDOUS WEATHER OUTLOOK FOR PUERTO RICO AND THE U.S. VIRGIN ISLANDS
NATIONAL WEATHER SERVICE SAN JUAN PR
421 AM AST SAT MAY 14 2011

AMZ710>745-PRZ001>013-150830-
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-
421 AM AST SAT MAY 14 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PUERTO RICO AND THE ADJACENT
ATLANTIC COASTAL WATERS.

.DAY ONE...TODAY AND TONIGHT
SCATTERED TO NUMEROUS SHOWERS ARE EXPECTED TO AFFECTED EAST AND
NORTHEAST SECTIONS OF PUERTO RICO TODAY AND TONIGHT. URBAN AND
SMALL STREAM FLOODING ARE LIKELY TODAY WITH THE HEAVIEST ACTIVITY.
ALSO...RAPID RISES IN RIVERS AS WELL AS MUDSLIDES IN STEEP TERRAIN
CAN BE EXPECTED. STRONG GUSTY WINDS NEAR 35 MPH WILL ACCOMPANY
THESE SHOWERS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY
SATURATED SOILS AND DEVELOPMENT OF SHOWERS AND ISOLATED THUNDERSTORMS
EACH AFTERNOON WILL KEEP THE LOCAL AREA PRONE TO URBAN AND SMALL
STREAM FLOODING AS WELL AS MUDSLIDES IN AREAS OF STEEP TERRAIN
THROUGH THE UPCOMING WEEKEND AND POSSIBLY INTO THE EARLY PART OF
NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

REPORTS OF HEAVY RAINFALL...FLOODING AND SIGNIFICANT WEATHER
HAZARDS WILL BE APPRECIATED OVER THE NEXT FEW DAYS.

AMZ715-725-VIZ001-002-150830-
ST. THOMAS ST. JOHN ADJACENT ISLANDS-ST CROIX-
NEARSHORE ATLANTIC AND ADJACENT CARIBBEAN COASTAL WATERS-
421 AM AST SAT MAY 14 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE U.S. VIRGIN ISLANDS AND THE
ADJACENT COASTAL WATERS.

.DAY ONE...TODAY AND TONIGHT
SCATTERED SHOWERS ARE EXPECTED TO AFFECTED MOST OF THE U.S.
VIRGIN ISLANDS TODAY AND TONIGHT. URBAN AND SMALL STREAM FLOODING
ARE LIKELY TODAY WITH THE HEAVIEST ACTIVITY. MUDSLIDES IN STEEP
TERRAIN CAN BE EXPECTED. STRONG GUSTY WINDS NEAR 35 MPH WILL
ACCOMPANY THESE SHOWERS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY
SATURATED SOILS WILL KEEP THE LOCAL AREA PRONE TO URBAN AND
MINOR FLOODING OF GUTS AND STREAMS DURING THE NEXT FEW DAYS.

.SPOTTER INFORMATION STATEMENT...
REPORTS OF RAINFALL...FLOODING AND SIGNIFICANT WEATHER HAZARDS WILL
BE APPRECIATED.

The radar

The San Juan radar (TJUA), 32 km away, was scanning. The volume nearest the first event began at 17:09 UTC.

Open the radar archive at this moment

Event by event

3 thunderstorm wind, 2 heavy rain, 2 flood, 1 debris flow, 1 flash flood. Local standard time, as filed.

Heavy Rain, Bayamon

When: May 14, 1:09 PM AST
Where: Bayamon County, 2.8 mi NNE of Bayamon to 2.91 mi NNE of Bayamon
Reported by: Public
Coordinates: 18.390, -66.161

North Main Avenue was reported flooded near Plaza Del Sol shopping mall.

Flood, Trujillo Alto

When: May 14, 1:27 PM AST to 4:30 PM AST
Where: Trujillo Alto County, 3.75 mi NW of Trujillo Alto to 3.86 mi NW of Trujillo Alto
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 18.367, -66.042

Road 844 at Barrio Villas de Carraizo was reported flooded in the municipality of Trujillo Alto.

Heavy Rain, Trujillo Alto

When: May 14, 1:29 PM AST to 4:30 PM AST
Where: Trujillo Alto County, 3.37 mi NW of Trujillo Alto to 2.4 mi NW of Trujillo Alto
Reported by: Emergency Manager
Coordinates: 18.362, -66.039

Flooding was reported at Road 1, in Urb. Hacienda de Carraizo in Trujillo Alto.

Debris Flow, Western Interior

When: May 14, 1:46 PM AST
Where: Western Interior forecast zone
Reported by: Emergency Manager

A mudslide was reported at Barrio Tanama, Road 526, Km 5.7 in the municipality of Adjuntas.

Thunderstorm Wind, Trujillo Alto

When: May 14, 2:15 PM AST to 2:30 PM AST
Where: Trujillo Alto County, Trujillo Alto
Measured: 52 kt (60 mph) estimated gust
Property damage: $15,000
Reported by: Public
Coordinates: 18.330, -66.000

Strong gusty winds and pea size hail were reported in Barrio La Gloria in Trujillo Alto. Downed trees, bamboo trees, and snapped branches were reported in Camino Culebra at Pellin Cruz, and in the Culebra sector of Barrio La Gloria Km. 2.2.

Thunderstorm Wind, Canovanas

When: May 14, 2:18 PM AST to 2:28 PM AST
Where: Canovanas County, 2.82 mi N of Canovanas to 3.37 mi N of Canovanas
Measured: 52 kt (60 mph) estimated gust
Property damage: $150,000
Reported by: Public
Coordinates: 18.370, -65.886

Strong gusty winds downed some trees and power poles in the west side of the parking lot of the Outlets Mall in Canovanas. A few vehicles were damaged as the trees fell down. The strong winds also damaged a car dealer along Highway 3, and also downed road signs. Pea size hail was also reported.

Thunderstorm Wind, Fajardo

When: May 14, 2:45 PM AST to 3:00 PM AST
Where: Fajardo County, 4.92 mi NW of Fajardo to 1.87 mi NNE of Fajardo
Measured: 53 kt (61 mph) measured gust
Property damage: $200,000
Reported by: Mesonet
Coordinates: 18.364, -65.709

Strong gusty winds and pea size hail were reported in the municipality of Fajardo as a very strong thunderstorm moved from through from west to east. A few homes lost their zinc roof. Three persons at the Dos Marinas condo swimming pool were swept by the wind gusts. Two of them suffered minor face and arms bruises. Vehicular traffic across some of the local roads was blocked by snapped branches and fallen trees. Sustained winds of around 30 mph with gusts to 61 mph were measured by the Puerto Rico Electric Power Authority mesonet in Fajardo around mid afternoon.

Flash Flood, San Juan

When: May 14, 3:36 PM AST to 4:30 PM AST
Where: San Juan County, 3.46 mi NW of San Juan to 3.07 mi NW of San Juan
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 18.417, -66.086

The Barrio Obrero sector in Santurce, Kennedy Avenue, Barbosa Avenue, Munoz Rivera Avenue and the University Garden sector were reported flooded.

Flood, Guaynabo

When: May 18, 1:54 PM AST to 4:45 PM AST
Where: Guaynabo County, 8.62 mi NW of Guaynabo to 8.27 mi NW of Guaynabo
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 18.424, -66.116

Road 165 near the federal prison was reported flooded in the municipality of Guaynabo.

What these are

Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
Debris Flow: A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.
Thunderstorm Wind: Winds from a thunderstorm of 50 knots (58 mph) or more, or lower winds that caused damage or casualties. Measured gusts are marked MG, estimated EG.
Flash Flood: Flooding that begins within six hours of the rain that causes it, or of a dam or levee failure or ice jam release, often with deadly speed.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in Puerto Rico in 2011 Every state in 2011 This day in weather history Warnings in Puerto Rico, May 2011

Sources

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: 291183, 291184, 291186, 291187, 319381, 319424, 319483, 317552, 292133.