Tropical Cyclone Kay formed on September 4th, 2022 and made its closest approach to Southern California on the 9th and 10th, with the center of Kay coming within 120 miles of San Diego. Tropical moisture associated with Kay managed to produce heavy rainfall leading to flooding across mountainous terrain in Southern California on September 9th and 10th. This led to a number of wind damage and flooding events in the mountains and desert foothill locations in Southern California. Kay transitioned to a Post-Tropical Cyclone that weekend, but left enough lingering moisture to support additional rounds of heavy thunderstorms through the 11th and 12th of September. These later rounds of heavy rain would lead to multiple significant debris flow events in the San Bernardino County Mountains, namely in and around the Apple and El Dorado burn scars.

Heavy Rain in RIVERSIDE, CALIFORNIA
From 11-SEP-22 16:20:00 to 11-SEP-22 16:20:00 (PST-8)
Location: MURRIETTA ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A strong thunderstorm in Murrieta produced 0.64 inches of rainfall.

Heavy Rain in RIVERSIDE, CALIFORNIA
From 12-SEP-22 04:00:00 to 12-SEP-22 04:00:00 (PST-8)
Location: ELSINORE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: COOP Observer

Co-Op Observer EORC1 Lake Elsinore measured 0.99 inches of rainfall.

Heavy Rain in SAN DIEGO, CALIFORNIA
From 12-SEP-22 09:26:00 to 12-SEP-22 09:26:00 (PST-8)
Location: (CZZ)CAMPO
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station CMFC1 Campo measured 0.87 inch of rainfall.

Heavy Rain in SAN DIEGO, CALIFORNIA
From 12-SEP-22 06:00:00 to 12-SEP-22 06:00:00 (PST-8)
Location: RAMONA ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRAHS station CA-SD-186 1.8 miles west-southwest of Ramona measured 0.95 inch of rainfall.

Debris Flow in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 14:00:00 to 12-SEP-22 19:00:00 (PST-8)
Location: FOREST FALLS
Flood cause: Heavy Rain / Burn Area
Property damage: 6.00M
Crop damage: 0.00K
Reported by: Department of Highways

Heavy thunderstorms associated with remnant moisture from post-tropical cyclone Kay produced torrential rain over the Apple and El Dorado burn scars on the afternoon of September 12. Multiple debris flows occurred following torrential one-hour rainfall rates exceeding debris flow guidance from the USGS and CAGS. Two of the debris flows traveled several miles including the Banning Canyon wash showing debris logs and ash water. The most impactful debris flow occurred in Forest Falls and Oak Glen, where the flow traveled at least 3 miles down Oakland Road with 4 foot boulders, logs over-topping the road with several feet of mud, with several power poles destroyed. Another highly impactful debris flow formed in Forest Falls on Prospect Road, where large boulders, black water and logs took out trees and damaged several homes. Another debris flow occurred 0.5 mile away on Valley of the Falls Road, producing a 12-foot wall of dirt and rocks. An additional debris flow occurred on State Highway Route 38 just before Angeles Oaks. These flows are the most significant that have occurred since the fires in 2020. An estimated 30 homes were damaged and three vehicles were moved and damaged.
The following are recorded rain amounts from the same region:
Raywood Flats, 6 NNW Forest Falls: 2.44 inch in 1 hour and 2.75 inch for the day, resulting in the full closure of Highway 38.
Mesonet Station Yucc1 Little San Gorgonio Peak Yucaipa Ridge, 2 SE Forest Falls: 1.06 inch in 60 minutes.
Mesonet Station FFPC1, 1.5 W Forest Falls: 1.93 inch.

Heavy Rain in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 12:00:00 to 12-SEP-22 12:00:00 (PST-8)
Location: RANCHO CUCAMONGA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Heavy rain associated with residual moisture from post-tropical cyclone Kay occurred during the afternoon on September 12 in northern portions of the Inland Empire, particularly north of Rancho Cucamonga.
The following are measured rainfall:
Mesonet station LRAC1, 5.5 NE Rancho Cucamonga: 2.83 inch.
Mesonet station DECC1, 4.2 N Rancho Cucamonga: 2.75 inch.
Mesonet station DACC1, 3.9 NE Rancho Cucamonga: 1.97 inch.

Flash Flood in RIVERSIDE, CALIFORNIA
From 12-SEP-22 11:30:00 to 12-SEP-22 19:30:00 (PST-8)
Location: CORONA MUNI ARPT
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Heavy rain associated with residual moisture from post-tropical cyclone Kay occurred during the afternoon on September 12 in southern portions of the Inland Empire. The Department of Highways reported a swift water rescue of a person seeking refuge on top of a vehicle. Local emergency managers also reported the southbound lane of I-15 was flooded at Dos Lagos.
The following are measured rain reports in the region:
Mesonet Station CW7445 Temescal Valley, 10 SE Corona: 1.78 inch.
Mesonet Station ECSC1 El Cariso RAWS, 5 WSW Lake Elsinore: 1.28 inch.

Flash Flood in RIVERSIDE, CALIFORNIA
From 12-SEP-22 14:44:00 to 12-SEP-22 14:44:00 (PST-8)
Location: ARCILLA
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

CHP report of a driver stuck in flash flooding with water coming into the vehicle.

Heavy Rain in SAN DIEGO, CALIFORNIA
From 12-SEP-22 11:52:00 to 12-SEP-22 11:52:00 (PST-8)
Location: DESCANSO
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station ANEC1 Alpine RAWS site measured 0.64 inch of rainfall.

Storm Surge/Tide in ORANGE COUNTY COASTAL, CALIFORNIA
From 09-SEP-22 09:13:00 to 09-SEP-22 09:13:00 (PST-8)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Seal Beach had surges come across the beach and into parking lots and Boardwalk 2100. High tide was around 6.6 FT on September 8. Berm was hastily erected, with pumps in place and sandbags ready for residents.

Strong Wind in SAN DIEGO COUNTY VALLEYS, CALIFORNIA
From 09-SEP-22 07:45:00 to 09-SEP-22 09:30:00 (PST-8)
Magnitude: 35.00 EG
Reported by: Department of Highways

Strong winds associated with Tropical Cyclone Kay impacted the San Diego County Valleys on September 9, with winds peaking in the morning hours. The following are reports of damage that morning:
2 W Rancho Bernardo: Downed tree limb (8-12 inches in diameter) partially blocking the road (NWS Employee).
4 ESE Valley Center: Downed power line and blocking the road (Public).
1 NE Valley Center: Downed tree blocking two lanes (Department of Highways).

Heavy Rain in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 12:04:00 to 12-SEP-22 12:04:00 (PST-8)
Location: RUNNING SPGS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station FW1313 Running Springs 1 measured 3.58 inches of storm total rainfall. Radar estimates were also near this amount.

Heavy Rain in RIVERSIDE, CALIFORNIA
From 12-SEP-22 06:00:00 to 12-SEP-22 06:00:00 (PST-8)
Location: GILMAN HOT SPGS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRAHS station CA-RV-58 4.2 miles west of San Jacinto measured 1.33 inches of storm total rainfall.

Heavy Rain in SAN DIEGO, CALIFORNIA
From 12-SEP-22 18:36:00 to 12-SEP-22 18:36:00 (PST-8)
Location: MT LAGUNA AFS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station TR120 Mt Laguna Portable measured 1.46 inches of storm total rainfall.

High Wind in SAN DIEGO COUNTY MOUNTAINS, CALIFORNIA
From 09-SEP-22 06:00:00 to 09-SEP-22 09:00:00 (PST-8)
Magnitude: 95.00 MG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Very strong winds associated with Tropical Cyclone Kay impacted the San Diego County Mountains on September 9, with winds peaking in the morning hours. The following are the strongest wind reports in the region:
Mesonet station HP029 Cuyamaca Peak, 9 S Julian: 109 mph
Mesonet station HP016 Big Black Mountain, 9 WNW Santa Ysabel: 96 mph
Mesonet station HF002 Laguna Launch, 7 NW Mt Laguna: 93 mph
Mesonet Station SILSD Sill Hill, 9 SSW Julian: 91 mph
Mesonet station HP019 Mt Laguna Observatory, 1 S Mt Laguna: 80 mph
Mesonet station OTYC1 Otay Mountain RAWS, 5 WSW Dulzura: 79 mph
Mesonet station HP014 Boucher Hill, 3 WNW Palomar Mountain: 74 mph
Mesonet station SYRSD Santa Ysabel Ranch, 2 N Santa Ysabel: 72 mph
Mesonet station HF003 Pine Valley, 4 SSE Pine Valley: 71 mph
Mesonet station EWRSD East Willows, 4 E Alpine: 63 mph
Mesonet station WDCSD West Descanso, 7 WNW Pine Valley: 59 mph
Mesonet station VISSD Viejas, 3 ENE Alpine: 58 mph
Mesonet station ANEC1 Alpine RAWS, 5 E Alpine: 56 mph
Multiple reports of damage were received from the Department of Highways during this time in the San Diego County Mountains, with trees down reported on SR-79, I-8, Highway 78, powerlines down near Alpine, and a report of round barrels rolling across lanes of traffic along I-8.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 17:08:00 to 12-SEP-22 17:08:00 (PST-8)
Location: WILD
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Three feet of water over the road on Route 66 at Frontier Road. Side of the road is eroding.

Heavy Rain in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 11:00:00 to 12-SEP-22 11:00:00 (PST-8)
Location: ETIWANDA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station LRAC1 Larson Ranch measured 2.83 inches of storm total rainfall.

Heavy Rain in RIVERSIDE, CALIFORNIA
From 12-SEP-22 06:00:00 to 12-SEP-22 06:00:00 (PST-8)
Location: LAKELAND VLG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRAHS station CA-RV-60 2.8 miles south-southwest of Lake Elsinore measured 2.09 inches of storm total rainfall.

Heavy Rain in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 03:29:00 to 12-SEP-22 03:29:00 (PST-8)
Location: SAN ANTONIO HGTS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

CoCoRAHS station CA-SR-53 1.8 miles north-northeast of Upland measured 1.35 inches of rainfall.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 12:00:00 to 12-SEP-22 19:30:00 (PST-8)
Location: LAKE ARROWHEAD
Flood cause: Heavy Rain / Burn Area
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Heavy rain associated with residual moisture from post-tropical cyclone Kay occurred during the afternoon on September 12 in the San Bernardino County Mountains. Rain amounts of 1.5 to 3 inches occurred in the region. The Department of Highways reported a flash flood near Crestline, with multiple vehicles stuck in flood water on Lake Drive at Forest Shade Drive. The following are measured rain amounts from various Mesonet sites:
Mesonet Station FW1313, 1 WNW Running Springs: 3.58 inch.
Strawberry Peak, 3 WSW Lake Arrowhead: 2.88 inch.
Heaps Peak RAWS, 3 NW Running Springs: 2.68 inch.
Mesonet Station CRQC1, 1 SSW Lake Arrowhead: 1.74 inch.
Mesonet Station PPOC1 Panorama Point, 2 SSW Crestline: 1.66 inch.
Mesonet Station FW0025 Lake Arrowhead South, 1 SE Lake Arrowhead: 1.52 inch.

Debris Flow in RIVERSIDE, CALIFORNIA
From 11-SEP-22 15:10:00 to 11-SEP-22 15:30:00 (PST-8)
Location: HEMET
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Heavy rain occurred from residual moisture associated with Tropical Cyclone Kay on September 11 in southern portions of the Inland Empire. Local emergency managers reported a mud flow over roads in Avery Canyon, and California Highway Patrol reported flooding at State Street and Cactus Valley Road.

Flash Flood in SAN DIEGO, CALIFORNIA
From 09-SEP-22 13:30:00 to 09-SEP-22 13:30:00 (PST-8)
Location: JACUMBA
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Storm Chaser

Water flowing across Old Highway 80 into Mexico, completely covering the roadway and making it impassable based on video. About 2 inches of widespread rain fell in the area.

Flood in SAN DIEGO, CALIFORNIA
From 09-SEP-22 14:26:00 to 09-SEP-22 14:26:00 (PST-8)
Location: OCOTILLO WELLS
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Borrego Salton Seaway / Arroyo Salado-Truckhaven Trail completely flooded out. Signage and Road Closed signs were placed. About 1 inch of rain fell in this area in 4 hours.

Heavy Rain in SAN DIEGO, CALIFORNIA
From 09-SEP-22 10:35:00 to 09-SEP-22 14:00:00 (PST-8)
Location: CAMPO
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Heavy rain associated with Tropical Cyclone Kay produced heavy rainfall across the San Diego County Mountains on September 9. The following are the heaviest rain reports from the day:
Mesonet station LGMC1 Mt. Laguna: 4.25 inch.
Mesonet Station MLGC1 Mt. Laguna Observatory RAWS, 2 NNW Mt. Laguna: 3.79 inch.
Mesonet Station AGUC1 Agua Caliente, 10 NE Mt. Laguna: 2.06 inch.
Mesonet Station TRRC1 Tierra Del Sol, 9 ENE Campo: 1.02 inch, 0.45 inch which occurred in one hour.

Flash Flood in SAN DIEGO, CALIFORNIA
From 11-SEP-22 14:00:00 to 11-SEP-22 14:00:00 (PST-8)
Location: RAMONA
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Portions of Wildcat Canyon Rd on the Barona Reservation under 3-10 inches of running water due to heavy rainfall. Visibility reduced to 1/4 mile during rain.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 11-SEP-22 17:36:00 to 11-SEP-22 17:36:00 (PST-8)
Location: CRESTLINE
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Highway 18 between Waterman Canyon and Highway 138, heavy rain led to debris flows including boulders up to 1 foot in diameter across all lanes. Water several inches deep was also flowing across lanes.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 11-SEP-22 17:30:00 to 11-SEP-22 18:30:00 (PST-8)
Location: DEVORE
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Heavy rain from residual moisture associated with Tropical Cyclone Kay occurred across northern portions of the Inland Empire, leading to multiple instances of flash flooding. Flash flooding was reported by a trained spotter on University Parkway and Kendall Drive near Devore, with one foot of water covering the roadway. Farther south toward Rialto, flooding occurred across all lanes on I-215 northbound. Flooding was also reported near San Bernardino across all lanes from University Parkway to Mount Vernon Ave.

Heavy Rain in SAN DIEGO, CALIFORNIA
From 09-SEP-22 12:17:00 to 09-SEP-22 12:17:00 (PST-8)
Location: MT LAGUNA AFS
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet Station LGMC1 Mt. Laguna at 6,000 Feet measured 0.98 inch of rainfall in one hour, and 3.23 inches total.

Heavy Rain in SAN DIEGO, CALIFORNIA
From 10-SEP-22 14:07:00 to 10-SEP-22 14:07:00 (PST-8)
Location: RANCHITA
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Mesonet

Mesonet station RCHC1 Ranchita measured 4.62 inches of storm total rainfall.

Heavy Rain in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 06:00:00 to 12-SEP-22 06:00:00 (PST-8)
Location: CRESTLINE
Property damage: 0.00K
Crop damage: 0.00K
Reported by: County Official

Crestline maintenance yard reported 2.10 inches of storm total rainfall.

Flood in RIVERSIDE, CALIFORNIA
From 10-SEP-22 08:51:00 to 10-SEP-22 08:51:00 (PST-8)
Location: BERMUDA DUNES ARPT
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Indio Road just south of Interstate 10 was closed due to flooding. A rain gauge in Indio Hills, 9 miles north of Indio, had 1.07 inches of rain in two hours on Saturday morning.

Flood in RIVERSIDE, CALIFORNIA
From 12-SEP-22 14:59:00 to 12-SEP-22 14:59:00 (PST-8)
Location: ALESSANDRO
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Spotter report of flash flooding with ankle-deep water. Nearby March Air Reserve Base picked up 0.28 inch of rainfall in about 10 minutes, with a storm total of 0.42 inch.

Flash Flood in SAN BERNARDINO, CALIFORNIA
From 12-SEP-22 14:12:00 to 12-SEP-22 14:12:00 (PST-8)
Location: LUCERNE VLY
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

CHP report of flooding on Highway 247, 3 vehicles possible submerged.

Flood in RIVERSIDE, CALIFORNIA
From 12-SEP-22 15:00:00 to 12-SEP-22 15:00:00 (PST-8)
Location: RIVERSIDE JCT
Flood cause: Heavy Rain / Tropical System
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Broadcast Media

KTLA report of flooding near the 5200 block of Chicago Avenue in Riverside. Two vehicles were stranded in flood waters. Nearby UC Riverside reported 0.49 inch of rain in one hour.

Thunderstorm Wind in RIVERSIDE, CALIFORNIA
From 09-SEP-22 12:00:00 to 09-SEP-22 12:00:00 (PST-8)
Location: ARLINGTON
Magnitude: 50.00 EG
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Strong winds associated with Tropical Storm Kay blew down a newly planted tree on the campus of Sherman Indian High School in Riverside.