Flash Flooding and Debris Flows in Puerto Rico, September 4 to 6, 2009

Name: Flash Flooding and Debris Flows in Puerto Rico, September 4 to 6, 2009
Start: 2009-09-04T09:27
End: 2009-09-06T20:50
Location: Puerto Rico

September 4 to 6, 2009 · NWS SJU · 20 events in 12 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: $35,000
Crop damage: None recorded
Events: 20

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 tropical wave emerged from the coast of Africa on August 25th, which moved westward near the Cape Verde Islands on the 26th. The system organized as it crossed the Atlantic, developing a low pressure area by the 28th. The system became well-enough organized to be classified a tropical storm during the afternoon of September 1st. A tropical storm watch was issued for the U.S. Virgin Islands and Puerto Rico at 5 pm September 2nd, followed by a tropical storm warning at 11 am on September 3rd. The system moved generally westward, and experienced moderate vertical wind shear through most of its existence as a tropical cyclone. As the surface circulation left most of the associated thunderstorms behind, the system tracked south of due west due to the low-level flow pattern Erika was embedded within. By the 3rd of September, Erika weakened into a tropical depression at 5 pm on September 3rd, and soon devolved into a remnant low during the evening. The remnant disturbance led to heavy rains over the U.S. Virgin Islands and Puerto Rico, which caused flooding in many communities. Minor to moderate flooding was reported in Puerto Rico.The core of the heavy rain fell along the Eastern third of the island. |The hardest hit basin was the Rio Grande de Loiza with a large percentage of its flow coming from the Rio Gurabo one of its larger tributaries . Minor to moderate flooding was reported along the Rio Gurabo, which crested at 23.52 feet 5 feet above its flood stage of 18 feet. The Rio Grande de Loiza, which flows from south to north, had a basin average rainfall of 4 to 5 inches with localized rainfall reports of 6 to over 7 inches. This led to a significant rise at the Carraizo Dam, where a number of gates had to be opened to maintain some balance.

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 Sep 4, 6:12 AM AST, 3 hours 15 minutes earlier.

Area forecast discussion, Sep 4, 6:12 AM AST, 3 hours 15 minutes before

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
612 AM AST FRI SEP 4 2009

.DISCUSSION...
A BROAD LOW TO MID LEVEL CIRCULATION APPARENT BETWEEN THE NORTHERN
LEEWARDS AND THE ISLAND OF SAINT CROIX...ASSOCIATED WITH THE LOW
PRESSURE CENTER/REMNANTS OF THE DOWNGRADED DEPRESSION ERIKA...
HAS CONTINUED TO ENHANCE SHOWERS AND PRODUCE INTENSE THUNDERSTORM
ACTIVITY EARLY THIS MORNING ACROSS THE NORTHEAST CARIBBEAN. EXPECT
ADDITIONAL SHOWERS AND THUNDERSTORMS TO DEVELOP ACROSS THE REGION
LATER IN THE DAY AIDED BY AN UPPER LEVEL DIFFLUENCE PATTERN...
DAYTIME HEATING...AN LOCAL TERRAIN EFFECTS.

BOTH THE GFS AND NAM MODEL GUIDANCE SUGGEST THE REFORMATION OF A
CYCLONIC CIRCULATION NORTH OF PUERTO RICO BY SUNDAY...WITH BOTH STILL
SUGGESTING CONSIDERABLE AMOUNTS OF MOISTURE TO LIFT ACROSS THE AREA
TODAY THROUGH AT LEAST SATURDAY. THE POSSIBILITY OF REDEVELOPMENT
OF A SURFACE LOW AND THE CONTINUED PRESENCE OF STRONG CONVECTION
ACROSS THE LEEWARDS AND THE NORTHEASTERN CARIBBEAN...AS WELL AS
THE LARGE TONGUE OF PWAT/MOISTURE STRETCHING ACROSS THE EASTERN
CARIBBEAN IS SUFFICIENT TO MAINTAIN FLASH FLOOD POTENTIAL AT LEAST
THROUGH SATURDAY. THEREFORE FLASH FLOOD WATCH WILL REMAIN IN EFFECT
THROUGH AT LEAST SATURDAY EVENING...AND WILL CONTINUE TO MONITOR
TO SEE HOW THE FEATURE MOVING ACROSS THE REGION UNFOLDS.

DEEP MOISTURE IS STILL HOWEVER EXPECTED TO SLOWLY FILTER IN ACROSS
THE REGION TRAILING THE ABOVE MENTIONED LOW TO MID LEVEL CIRCULATION
OF THIS COMPLEX SYSTEM...AND WILL LIKELY LINGER ACROSS THE REGION
THROUGH SATURDAY...FOLLOWED BY A SLIGHTLY DRIER TREND BEGINNING ON
SUNDAY. HOWEVER...SUFFICIENT LOW LEVEL MOISTURE WILL BE AVAILABLE
ON SUNDAY FOR THE DEVELOPMENT OF NOCTURNAL AND DIURNAL CONVECTION
ACROSS THE EAST COASTAL AREAS AND WEST INTERIOR SECTIONS OF PUERTO
RICO RESPECTIVELY...AS WELL AS PARTS OF THE VIRGIN ISLANDS.

&&

.AVIATION...
BROAD LOW TO MID LEVEL ROTATION...WILL CONTINUE TO GENERATE A
LARGE AREA OF CLOUDINESS...SHOWERS AND THUNDERSTORMS ACROSS THE
LOCAL ISLANDS AND ALL LOCAL TAF SITES DURING THE NEXT 24 HOURS.
EXPECT AREAS OF SHRA AND TSRA TO DEVELOP EARLY IN THE MORNING
PRODUCING PERIODS OF MVFR OR EVEN IFR CONDITIONS ACROSS TKPK...
TNCM...TISX AND TIST UNTIL AT LEAST BY 04/1500Z. THIS MOISTURE
WILL PROPAGATE SLOWLY WESTWARD PRODUCING INTERMITTENT PERIODS OF
MVFR CONDITIONS ACROSS THE REST OF THE LOCAL TAF SITES AFTER 04/1500Z.
PERIODS OF SHRA AND TSRA WILL CONTINUE TO DEVELOP THROUGH THE AFTERNOON
AND EVENING HOURS. TJSJ 04/000Z SOUNDING INDICATED AN EAST NORTHEAST
WIND FLOW...UP TO 20 KNOTS...ALL THE WAY FROM THE SURFACE TO AROUND
25K FEET... BECOMING FROM THE WEST ALOFT.

&&

.MARINE...
FRESH TO STRONG WINDS AND ROUGH SEAS WILL CONTINUE ACROSS THE
LOCAL WATERS TODAY AS THE REMNANTS OF WHAT WAS ONCE TROPICAL
DEPRESSION ERIKA MOVES WEST NORTHWEST ACROSS THE LOCAL WATERS.
EXPECT MARINE CONDITIONS TO SLOWLY IMPROVE LATER THIS EVENING
AND SATURDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  88  77  90  78 /  70  50  40  50
STT  86  80  88  81 /  70  70  50  50

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...FLASH FLOOD WATCH THROUGH SATURDAY EVENING FOR CENTRAL INTERIOR-
     CULEBRA-EASTERN INTERIOR-MAYAGUEZ AND VICINITY-NORTH
     CENTRAL-NORTHEAST-NORTHWEST-PONCE AND VICINITY-SAN JUAN AND
     VICINITY-SOUTHEAST-SOUTHWEST-VIEQUES-WESTERN INTERIOR.

VI...FLASH FLOOD WATCH THROUGH SATURDAY EVENING FOR ST CROIX-ST.
     THOMAS/ST. JOHN/ADJACENT ISLANDS.

&&

72/09

Hazardous weather outlook, Sep 4, 6:55 AM AST, 2 hours 32 minutes before

HAZARDOUS WEATHER OUTLOOK FOR PUERTO RICO AND THE U.S. VIRGIN
ISLANDS
NATIONAL WEATHER SERVICE SAN JUAN PR
655 AM AST FRI SEP 4 2009

AMZ710>745-PRZ001>013-051100-
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-
655 AM AST FRI SEP 4 2009

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

.DAY ONE...TODAY AND TONIGHT
A FLASH FLOOD WATCH REMAINS IN EFFECT FOR ALL OF PUERTO RICO. A
LARGE AREA OF CLOUDINESS...ASSOCIATED WITH THE REMNANTS OF
TROPICAL DEPRESSION ERIKA EXTENDS FROM EASTERN PUERTO RICO...EAST
AND SOUTHEASTWARD ACROSS THE NORTHERN LEEWARD ISLANDS AND ACROSS
THE CARIBBEAN WATERS FOR SEVERAL HUNDRED MILES. THIS MOISTURE WITH
EMBEDDED SHOWERS AND STRONG THUNDERSTORMS WILL PROPAGATE SLOWLY
WEST NORTHWESTWARD TODAY AND TONIGHT. THE POTENTIAL FOR LOCALLY
HEAVY RAINFALL WILL CONTINUE FOR PUERTO RICO AS THIS ACTIVITY WILL
GRADUALLY MOVE SLOWLY ACROSS THE REGION. RAINFALL AMOUNTS OF TWO
TO FOUR INCHES ARE EXPECTED WITH LOCALIZED GREATER AMOUNTS...
ESPECIALLY OVER THE HIGHER TERRAIN OF PUERTO RICO THIS AFTERNOON
AND TONIGHT. THIS RAINFALL HAS THE POTENTIAL TO PRODUCE
SIGNIFICANT FLASH AND RIVER FLOODING ACROSS PUERTO RICO. IN
ADDITION...MUDSLIDES ARE POSSIBLE OVER AREAS OF STEEP TERRAIN.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY
LINGERING MOISTURE ASSOCIATED WITH THE REMNANT OF TROPICAL
DEPRESSION ERIKA WILL PERSIST ACROSS THE REGION THROUGH THE
WEEKEND PRODUCING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS.
RAIN WILL CONTINUE INTO SATURDAY AND POSSIBLE ON SUNDAY...WITH
FLOODING POSSIBLE ON EACH DAY.

.SPOTTER INFORMATION STATEMENT...SPOTTERS REPORTS OF HEAVY RAIN
AND/OR FLOODING ARE WELCOME.

AMZ715-725-VIZ001-002-051100-
ST. THOMAS ST. JOHN ADJACENT ISLANDS-ST CROIX-
NEARSHORE ATLANTIC AND ADJACENT CARIBBEAN COASTAL WATERS-
655 AM AST FRI SEP 4 2009

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

.DAY ONE...TODAY AND TONIGHT

A FLASH FLOOD WATCH REMAINS IN EFFECT FOR ALL OF THE U.S. VIRGIN
ISLANDS. A LARGE AREA OF CLOUDINESS...ASSOCIATED WITH THE
REMNANTS OF TROPICAL DEPRESSION ERIKA...EXTENDS FROM THE LOCAL
ISLANDS...EAST AND SOUTHEASTWARD ACROSS THE NORTHERN LEEWARD
ISLANDS AND ACROSS THE CARIBBEAN WATERS FOR SEVERAL HUNDRED MILES.
THIS MOISTURE WITH EMBEDDED SHOWERS AND STRONG THUNDERSTORMS WILL
PROPAGATE SLOWLY WEST NORTHWESTWARD TODAY AND TONIGHT. THE
POTENTIAL FOR LOCALLY HEAVY RAINFALL WILL CONTINUE FOR THE LOCAL
ISLANDS AS THIS ACTIVITY WILL GRADUALLY MOVE SLOWLY ACROSS THE
REGION.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY
LINGERING MOISTURE ASSOCIATED WITH THE REMNANT OF TROPICAL
DEPRESSION ERIKA WILL PERSIST ACROSS THE REGION THROUGH THE
WEEKEND PRODUCING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS.
RAIN WILL CONTINUE INTO SATURDAY AND POSSIBLE ON SUNDAY...WITH
FLOODING POSSIBLE ON EACH DAY.

.SPOTTER INFORMATION STATEMENT...
SPOTTERS REPORTS OF HEAVY RAIN AND/OR FLOODING ARE WELCOME.

The radar

The San Juan radar (TJUA), 36 km away, was scanning. The volume nearest the first event began at 13:26 UTC.

Open the radar archive at this moment

Event by event

14 flash flood, 4 debris flow, 2 heavy rain. Local standard time, as filed.

Heavy Rain, Naguabo

When: September 4, 9:27 AM AST
Where: Naguabo County, 1.66 mi WSW of Naguabo
Reported by: Broadcast Media
Coordinates: 18.212, -65.754

Broadcast media reported road 31 in Naguabo was flooded.

Flash Flood, Guanica

When: September 4, 8:53 PM AST to 9:45 PM AST
Where: Guanica County, 2.13 mi E of Guanica to 2.16 mi E of Guanica
Cause: Heavy Rain
Property damage: $5,000
Reported by: Emergency Manager
Coordinates: 17.977, -66.888

Houses were flooded at Maria Antonia and Bo.Ensenada in the municipality of Guanica.

Flash Flood, Caguas

When: September 5, 4:24 AM AST to 6:45 AM AST
Where: Caguas County, 3.33 mi N of Caguas to 3.31 mi N of Caguas
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 18.248, -66.027

USGS gage at Rio Caguitas Villa Blanca in Caguas rose to 16.43 feet exceeding the flood stage of 15 feet.

Flash Flood, San Lorenzo

When: September 5, 6:10 AM AST to 8:19 AM AST
Where: San Lorenzo County, 2.52 mi NNE of San Lorenzo to 2.51 mi NNE of San Lorenzo
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 18.186, -65.962

USGS Rio Grande de Loiza gage, near Highway 183 at San Lorenzo rose to 19.10 feet exceeding the flood stage of 14 feet. River Caguitas in San Lorenzo was also reported out of its banks.

Flash Flood, Caguas

When: September 5, 6:17 AM AST to 9:00 AM AST
Where: Caguas County, 5.22 mi S of Caguas to 4.81 mi SSW of Caguas
Cause: Heavy Rain
Property damage: $5,000
Reported by: Emergency Manager
Coordinates: 18.125, -66.040

Roads and houses were flooded at Urb. La Plaza, Road Ramon Santini in the municipality of Caguas.

Flash Flood, San Lorenzo

When: September 5, 6:40 AM AST to 7:39 AM AST
Where: San Lorenzo County, 1.96 mi NNE of San Lorenzo to 1.99 mi NNE of San Lorenzo
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 18.178, -65.964

USGS river gage at Rio Cayaguas, Cerro Gordo, San Lorenzo, rose to 15.64 feet, exceeding the 15 feet flood stage.

Debris Flow, Eastern Interior

When: September 5, 6:42 AM AST
Where: Eastern Interior forecast zone
Reported by: Emergency Manager

A mudslide was reported at Barrio Sobaco, Road 7784 in the municipality of Cidra. People were trapped in the mudslide, but were rescued without any injuries.

Flash Flood, Santa Isabel

When: September 5, 6:43 AM AST to 9:00 AM AST
Where: Santa Isabel County, 4.09 mi W of Santa Isabel to 4.08 mi W of Santa Isabel
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 17.980, -66.442

A house was reported flooded at Bo. Playita Cortada, Road #6, in the municipality of Santa Isabel.

Flash Flood, Las Piedras

When: September 5, 6:43 AM AST to 9:00 AM AST
Where: Las Piedras County, 3.64 mi NNW of Las Piedras to 3.61 mi NNW of Las Piedras
Cause: Heavy Rain
Property damage: $15,000
Reported by: Emergency Manager
Coordinates: 18.231, -65.863

Roads and homes were flooded at Las Estancias, Barrio Pueblito in the municipality of Las Piedras.

Flash Flood, Caguas

When: September 5, 6:52 AM AST to 9:33 AM AST
Where: Caguas County, 3.12 mi NNE of Caguas to 3.17 mi NNE of Caguas
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 18.241, -66.010

USGS gage at Rio Grande de Loiza at Caguas rose to 18.74 feet, above the flood stage of 16 feet.

Flash Flood, Trujillo Alto

When: September 5, 6:58 AM AST to 1:10 PM AST
Where: Trujillo Alto County, 0.95 mi NNW of Trujillo Alto to 0.86 mi NNW of Trujillo Alto
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 18.343, -66.006

USGS gage at Rio Grande de Loiza below the dam rose to 29.27 feet, above the flood stage of 22 feet.

Flash Flood, Caguas

When: September 5, 7:25 AM AST to 9:25 AM AST
Where: Caguas County, 1.84 mi N of Caguas to 1.83 mi N of Caguas
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 18.227, -66.028

The Caguas City HIMA Hospital parking lot was reported flooded by nearby river.

Heavy Rain, Carolina

When: September 5, 7:35 AM AST to 8:35 AM AST
Where: Carolina County, 1.47 mi NW of Carolina
Reported by: Emergency Manager
Coordinates: 18.384, -65.967

Urban flooding was reported along roads 853, 856, and 857. The Roberto Clemente and Severo Quinones avenues were also reported flooded and impassable.

Debris Flow, Eastern Interior

When: September 5, 8:55 AM AST
Where: Eastern Interior forecast zone
Reported by: Emergency Manager

A mudslide was reported at Bo Jaguar, El Salto sector, Road 181 Km 6.6 in the municipality of San Lorenzo.

Flash Flood, Gurabo

When: September 5, 9:23 AM AST to 10:50 AM AST
Where: Gurabo County, 0.91 mi S of Gurabo to 0.94 mi S of Gurabo
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 18.257, -65.968

USGS River Gurabo sensor indicated the river level rose to 23.52 feet, above the 18 feet flood stage.

Flash Flood, Fajardo

When: September 5, 9:26 AM AST to 10:58 AM AST
Where: Fajardo County, 4.13 mi SW of Fajardo to 4.24 mi SW of Fajardo
Cause: Heavy Rain
Reported by: River/Stream Gage
Coordinates: 18.283, -65.699

USGS river gage at Rio Fajardo, Paraiso, rose to 9 feet, exceeding the flood stage of 8 feet.

Debris Flow, Eastern Interior

When: September 5, 9:49 AM AST
Where: Eastern Interior forecast zone
Reported by: Emergency Manager

A mudslide was reported at Road 181, Santa Rita sector in the municipality of Gurabo.

Flash Flood, Fajardo

When: September 5, 11:35 AM AST to 12:35 PM AST
Where: Fajardo County, 0.49 mi WNW of Fajardo to 0.37 mi W of Fajardo
Cause: Heavy Rain
Property damage: $10,000
Reported by: Emergency Manager
Coordinates: 18.322, -65.657

A home was reported flooded in the Alturas de San Pedro neighborhood.

Debris Flow, Ponce and Vicinity

When: September 5, 9:15 PM AST
Where: Ponce and Vicinity forecast zone
Reported by: Emergency Manager

A mudslide was reported along Highway 10 near the bridge at the intersection with road 503, between Adjuntas and Ponce municipalities.

Flash Flood, Fajardo

When: September 6, 7:50 PM AST to 8:50 PM AST
Where: Fajardo County, 0.34 mi SSW of Fajardo to 0.33 mi SSW of Fajardo
Cause: Heavy Rain
Reported by: Emergency Manager
Coordinates: 18.315, -65.651

River Rio Fajardo was reported out of its banks at the intersection of Highway 3 with road 194. The USGS river gage at Paraiso near Fajardo indicated the river rose to 8.82 feet, exceeding its flood stage of 8 feet.

What these are

Heavy Rain: Rainfall totals unusual for the place and season that did not produce a flood.
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.
Debris Flow: A fast-moving slurry of mud, rock and debris, usually on a slope soaked by heavy rain or stripped by a fire.

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

The same day elsewhere

Every storm in Puerto Rico in 2009 Every state in 2009 This day in weather history Warnings in Puerto Rico, September 2009

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: 196886, 197366, 196833, 196825, 197364, 196827, 197350, 197141, 197142, 196823, 196822, 196885, 196887, 197351, 196817, 196836, 197349, 196889, 197348, 196880.