Tropical Storm and Flash Flooding in California, August 19 to 22, 2023

Name: Tropical Storm and Flash Flooding in California, August 19 to 22, 2023
Start: 2023-08-19T20:00
End: 2023-08-22T06:00
Location: California

August 19 to 22, 2023 · NWS SGX · 39 events in 17 counties and zones

Tropical Storm Hilary made landfall across northern Baja California on August 20, and moved through Southern California that afternoon and evening. Torrential rainfall occurred across mountain and desert communities, resulting in catastrophic flash flooding and debris flows, damaged railways and bridges, and the closing of major interstates including I-8 in San Diego County and I-10 in Riverside…

Where it happened

Every event with a place to put it; 13 filed by county or forecast zone are drawn at its center, in a lighter ring. 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: None recorded
Crop damage: None recorded
Events: 39

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 SGX wrote it up.

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 Diego, CA wrote its last area forecast discussion before the first event at Aug 19, 1:03 PM PST, 6 hours 57 minutes earlier.

Area forecast discussion, Aug 19, 1:03 PM PST, 6 hours 57 minutes before

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The radar

The Santa Ana Mts radar (KSOX), 62 km away, was scanning. The volume nearest the first event began at 03:58 UTC.

Open the radar archive at this moment

Event by event

13 tropical storm, 11 flash flood, 10 flood, 4 heavy rain, 1 debris flow. Local standard time, as filed.

Heavy Rain, San Bernardino

When: August 19, 8:00 PM PST to August 22, 6:00 AM PST
Where: San Bernardino County, 2.53 mi NW of Wrightwood to 4.63 mi SW of Landers
Reported by: Mesonet
Coordinates: 34.371, -117.666

Heavy rain associated with Tropical Cyclone Hilary impacted much of San Bernardino County starting late on August 19th. The heaviest rainfall occurred on August 20th which led to numerous reports of flash flooding and debris flows. Light rainfall continued through the 21st as well. The heaviest rainfall occurred in the San Bernardino County Mountains, where anywhere from about 2.00-6.00 of rain fell on average. Heavier amounts include 13.07 at Upper Mission Creek (UMCC1), 10.34 at Crestline (CA-SR-84), 9.71 at the Lytle Creek RAWS site, 8.23 at Running Springs, 6.92 at Wrightwood (CA-SR-69), and 6.44 at Forest Falls (FFPC1). Rainfall totals in the Apple and Lucerne Valleys generally ranged from 1.00-3.00. Notable higher totals in this area include Mojave Forks Dam southeast of Hesperia (MVDC1) receiving 6.43 of rain, and Phelan (CW6479) receiving 3.74. Rainfall totals farther south across the Inland Empire generally ranged from 1.50-3.50. The Devore Fire Station observed a localized higher rainfall total of 4.24.

Heavy Rain, Riverside

When: August 19, 8:00 PM PST to August 22, 6:00 AM PST
Where: Riverside County, 11.58 mi NNW of Prado Dam to 4.55 mi NNE of Mecca
Reported by: Mesonet
Coordinates: 34.028, -117.744

Heavy rain associated with Tropical Cyclone Hilary impacted much of Riverside County starting late on August 19th. The heaviest rainfall occurred on August 20th which led to numerous reports of flash flooding and debris flows. Light rainfall continued through the 21st as well. The heaviest rainfall occurred in the Riverside County Mountains, where anywhere from about 2.00-6.00 of rain fell on average. Heavier amounts include 11.75 at Mount San Jacinto (MSJC1), 8.24 at Sky Valley (EW3393).

Rainfall totals in the Coachella Valley generally ranged from 3.00-6.00. Notable rainfall totals where more extreme impacts occurred include 4.32 at Cathedral City (FW8322), 4.02 at Palm Desert (GW2765), and 3.23 at Palm Springs International Airport.

Rainfall totals farther west across the Inland Empire generally ranged from 1.00-3.00. Notable higher totals in this area include 5.27 at Wildomar (1161D), 4.19 at Murrieta (FW8806), 3.59 at Lake Elsinore (FW0823), and 3.34 at Cabazon (BAZC1).

Heavy Rain, Orange

When: August 19, 8:00 PM PST to August 22, 6:00 AM PST
Where: Orange County, 1.02 mi NNE of Disneyland to 0.3 mi E of Dana Pt
Reported by: Mesonet
Coordinates: 33.833, -117.891

Heavy rain associated with Tropical Cyclone Hilary impacted much of Orange County starting late on August 19th. The heaviest rainfall occurred on August 20th which led to numerous reports of flash flooding and debris flows. Light rainfall continued through the 21st as well. The heaviest rainfall occurred in the Santa Ana Mountains, where anywhere from about 2.00-4.00 of rain fell on average. Heavier amounts include 4.53 of rain at Upper Harding Canyon (UHCC1), 4.17 at Santiago Peak (SAOC1), and 4.09 at both Horsethief Canyon (HTFC1) and Upper Silverado Canyon (SDOC1). Rainfall totals across inland Orange County as well as along the coast generally ranged from 1.00-3.00. Localized higher totals of 5.14 occurred in Huntington Beach (CW1521) and also north of Mission Viejo (MSTC1) where 3.42 of rain fell.

Heavy Rain, San Diego

When: August 19, 8:00 PM PST to August 22, 6:00 AM PST
Where: San Diego County, 1.61 mi W of (Nrs)naf Imperial Be to 18.19 mi N of Ocotillo Wells
Reported by: Mesonet
Coordinates: 32.551, -117.128

Heavy rain associated with Tropical Cyclone Hilary impacted much of San Diego County starting late on August 19th. The heaviest rainfall occurred on August 20th which led to numerous reports of flash flooding and debris flows. Light rainfall continued through the 21st as well. The heaviest rainfall occurred in the San Diego County Mountains, where anywhere from about 3.00-6.00 of rain fell on average. Heavier amounts include 6.67 of rain at Palomar Mountain (PRMC1), 6.64 at Mount Laguna Observatory (MLGC1), and 6.08 at Ranchita (RCHC1).

Rainfall totals across the San Diego County Deserts generally ranged from 1.00-2.30. Notable totals include 2.25 of rain at San Felipe (SFVC1), 2.20 of rain at Anza Borrego Desert Park (UCAB), and 1.55 of rain at Ocotillo Wells (OCWC1).

Rainfall totals across the San Diego County Valleys ranged from 1.50-3.60. Notable totals from this region include 3.56 of rain at Valley Center (CW9939), 3.51 at Lake Wohlford (WHLC1), 3.47 of rain in Fallbrook, 3.10 of rain in Escondido (EW6576), 2.42 in Poway (CA-SD-12), and 2.23 in Ramona (CA-SD-186).

Rainfall totals across the San Diego County coastal and beach areas generally ranged from 1.50-3.25. An observation near Carlsbad (CA-SD-86) received total rainfall of 3.16, Encinitas (3962D) received 3.12, San Marcos (AS654) recorded a rainfall total of 2.88, and San Diego International Airport received 1.84 of rain.

Flash Flood, Riverside

When: August 20, 12:00 AM PST to August 21, 6:00 AM PST
Where: Riverside County, 0.99 mi W of Thousand Palms to 0.25 mi E of Thousand Palms
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 33.819, -116.417

A roughly 30-mile stretch of I-10 between Bob Hope Drive and Indian Canyon Drive was closed due to inundation by mud, debris, and flooding. Flooding covered Gene Autry Road in Palm Springs.

Flash Flood, Riverside

When: August 20, 12:00 AM PST to August 21, 12:00 AM PST
Where: Riverside County, 1.7 mi N of Banning to 3.04 mi N of Banning
Cause: Heavy Rain / Tropical System
Reported by: Emergency Manager
Coordinates: 33.954, -116.876

The Mias Canyon Bridge near the Apple Burn Scar was washed out due to heavy rain and flowing debris.

Flash Flood, Riverside

When: August 20, 12:00 AM PST to August 21, 12:00 AM PST
Where: Riverside County, 2.05 mi WSW of Salvia to 1.07 mi NNW of Salvia
Cause: Heavy Rain / Tropical System
Reported by: Broadcast Media
Coordinates: 33.864, -116.500

Union Pacific rail tracks were undercut and washed out when the Whitewater River broke a division bern at the California and Colorado River Aqueduct. At least one train was confirmed to have derailed, with two other trains either observed off track after being forced off the rails by floodwaters, or buried on track. Water and debris was estimated to be 10-15 feet high, and also buckled/cracked the bridge footing at Whitewater. This also severed fiber cables in the area, leading to outages.

Flood, San Diego

When: August 20, 5:00 AM PST to August 21, 12:00 PM PST
Where: San Diego County, 1.74 mi E of Overlook to 1.86 mi E of Overlook
Cause: Heavy Rain / Tropical System
Reported by: Fire Department/Rescue
Coordinates: 32.770, -117.170

San Diego Swiftwater Rescue Lifeguard and Fire Department reported 14 rescues on Sunday 8/20. The San Diego River reached 9.8 feet with a very rapid rise after the watershed received 1.5 to 3.0 inches of rainfall.

Tropical Storm, San Diego County Mountains

When: August 20, 5:00 AM PST to 9:00 PM PST
Where: San Diego County Mountains forecast zone
Reported by: Mesonet
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Tropical Storm Hilary produced widespread tropical storm-force winds across Southern California from early morning on August 20 through the early overnight hours into August 21. The following are the top wind gusts reported across the San Diego County Mountains.

Big Black Mountain: 84 MPH (1125 AM 08/20)|Palomar Mtn Lookout: 79 MPH (6:05 AM 08/20)|West San Ysabel (SDGE): 71 MPH (9:50 AM 08/20)|Sill Hill (SDGE): 70 MPH (8:50 AM 08/20)|Harrison Park (SDGE): 68 MPH (1:50 PM 08/20)|Hoskings Ranch (SDGE): 67 MPH (11:50 AM 08/20)|Boulder Creek (SDGE): 65 MPH (6:00 AM 08/20)|Mt Laguna Observatory: 63 MPH (6:45 AM 08/20)|Pine Valley - Horse Launch: 62 MPH (12:45 PM 08/20)|Lake Cuyamaca: 60 MPH (1:30 PM 08/20)|Birch Hill: 60 MPH (8:48 AM 08/20)|Lucky Five Ranch (SDGE): 60 MPH (9:00 AM 08/20)|Mataguay (SDGE): 60 MPH (11:00 AM 08/20)|North Descanso (SDGE): 60 MPH (7:50 AM 08/20)|Buckman Springs (SDGE): 59 MPH (11:20 AM 08/20)|Crestwood (SDGE): 59 MPH (8:00 AM 08/20)|Morena Dam: 57 MPH (12:00 PM 08/20)|La Posta (SDGE): 57 MPH (9:00 AM 08/20)|School House Cyn (SDGE): 57 MPH (9:10 AM 08/20)|Lake Cuyamaca (SDGE): 56 MPH (2:10 PM 08/20)|Mesa Grande (SDGE): 56 MPH (11:10 AM 08/20)|Warners (SDGE): 56 MPH (9:50 AM 08/20)|Chihuahua Valley (SDGE): 55 MPH (2:20 PM 08/20)|East Warners (SDGE): 55 MPH (3:10 PM 08/20)|Sky Oaks: 54 MPH (1:44 PM 08/20)|Sherilton Valley: 54 MPH (12:00 PM 08/20)|Descanso North: 53 MPH (10:27 AM 08/20)|Boulevard West (SDGE): 52 MPH (10:10 AM 08/20)|White Star: 52 MPH (9:18 AM 08/20)|Ranchita (SDGE): 52 MPH (2:20 PM 08/20)|Viejas Grade (SDGE): 52 MPH (10:50 AM 08/20)|West Wynola (SDGE): 52 MPH (8:40 AM 08/20)|Oak Grove: 51 MPH (6:13 PM 08/20)|Wynola (SDGE): 51 MPH (11:50 AM 08/20).

A large oak tree was downed near Julian, blocking lanes on Wynola Road near Highway 78.

Flood, Riverside

When: August 20, 6:00 AM PST to 12:00 PM PST
Where: Riverside County, 1.09 mi WSW of La Quinta to 1.96 mi SSW of La Quinta
Cause: Heavy Rain / Tropical System
Reported by: Public
Coordinates: 33.661, -116.316

Heavy rainfall from Tropical Storm Hilary lead to flooding waters several feet deep at the La Quinta Resort and Club.

Tropical Storm, Santa Ana Mountains and Foothills

When: August 20, 7:00 AM PST to August 21, 12:00 AM PST
Where: Santa Ana Mountains and Foothills forecast zone
Reported by: RAWS
Coordinates: 33.483, -116.847 (the zone’s center; the record gives no point)

Tropical Storm, San Diego County Valleys

When: August 20, 7:00 AM PST to 10:00 PM PST
Where: San Diego County Valleys forecast zone
Reported by: Utility Company
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Tropical Storm, Riverside County Mountains

When: August 20, 7:00 AM PST to 8:30 PM PST
Where: Riverside County Mountains forecast zone
Reported by: Utility Company
Coordinates: 33.744, -115.994 (the zone’s center; the record gives no point)

Tropical Storm Hilary produced widespread tropical storm-force winds across Southern California from early morning on August 20 through the evening. The following are the top wind gusts reported across the Riverside County Mountains:

Pine Cove Rocky Point: 62 MPH (3:00 PM 08/20)|Apple Canyon (SCE376): 60 MPH (3:30 PM 08/20)|Red Mountain (SCE248): 59 MPH (3:40 PM 08/20)|San Marcos 3: 58 MPH (4:17 PM 08/20)|Chimney Flats (SCE247): 56 MPH (12:00 PM 08/20)|Keen Ridge (SCE375): 55 MPH (3:20 PM 08/20)|Twin Pines (SCE035): 52 MPH (10:10 AM 08/20)|Anza: 51 MPH (2:54 PM 08/20)|Pine Cove (SCE1170): 48 MPH (8:20 AM 08/20)|Pine Cove Water Office: 45 MPH (3:45 PM 08/20)|Idyllwild (SCE002): 45 MPH (3:40 PM 08/20).

Tropical Storm, San Gorgonio Pass Near Banning

When: August 20, 8:00 AM PST to 6:00 PM PST
Where: San Gorgonio Pass Near Banning forecast zone
Reported by: RAWS
Coordinates: 33.744, -115.994 (the zone’s center; the record gives no point)

Whitewater RAWS: 70 MPH (5:50 PM 08/20)|Whitewater (SCE1015):67 MPH (6:10 PM 08/20)|Banning (SCE1645): 57 MPH (5:20 PM 08/20)|Cabazon (SCE1445): 56 MPH (5:00 PM 08/20)|Desert Hot Springs (SCE643): 56 MPH (6:10 PM 08/20)|Cabazon: 54 MPH (5:14 PM 08/20)|Banning North (SCE114): 54 MPH (2:50 PM 08/20)|Whitewater Cyn (SCE363): 54 MPH (6:20 PM 08/20)|Snowcreek Cyn (SCE577): 54 MPH (5:50 PM 08/20)|Morongo Valley (SCE287): 53 MPH (6:40 PM 08/20)|Desert Hot Springs (SCE566): 53 MPH (6:20 PM 08/20)|Cabazon (SCE1010): 52 MPH (4:30 PM 08/20)|Stubbe Cyn (SCE1161): 51 MPH (5:20 PM 08/20)|San Gorgonio Pass (SCE1464): 51 MPH (4:30 PM 08/20)|Desert Hot Springs (SGXWFO): 51 MPH (6:45 PM 08/20)|Desert Hot Springs (SCE561): 51 MPH (6:10 PM 08/20)|Whitewater South (SCE586): 51 MPH (4:50 PM 08/20)|Millard Pass (SCE884): 51 MPH (4:20 PM 08/20)|Beaumont (SCE1139): 50 MPH (9:20 AM 08/20)|Banning (SCE635): 50 MPH (5:20 PM 08/20).

Tropical Storm, San Bernardino and Riverside County Valleys - the Inland Empire

When: August 20, 8:00 AM PST to August 21, 12:00 AM PST
Where: San Bernardino and Riverside County Valleys - the Inland Empire forecast zone
Reported by: Utility Company
Coordinates: 34.293, -116.086 (the zone’s center; the record gives no point)

Highland Springs: 60 MPH (9:16 AM 08/20)|Homeland (SCE757): 56 MPH (8:50 PM 08/20)|Beaumont (SCE1646): 52 MPH (9:00 AM 08/20)|Wildomar (SCE1359): 51 MPH (10:40 PM 08/20)|Box Springs Mtn (SCE268): 51 MPH (9:40 PM 08/20)|Grand Terrace (SCE925): 51 MPH (10:00 PM 08/20)|Sage East (SCE074): 50 MPH (2:20 PM 08/20)|Calimesa (SCE1233): 49 MPH (4:20 PM 08/20)|Cherry Valley (SCE1238): 49 MPH (5:30 PM 08/20)|Brown Canyon (SCE480): 49 MPH (4:40 PM 08/20).

Tropical Storm, San Bernardino County Mountains

When: August 20, 8:00 AM PST to August 21, 3:00 AM PST
Where: San Bernardino County Mountains forecast zone
Reported by: Utility Company
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Sce Silverwood West: 80 MPH (10:30 PM 08/20)|Pigsah Peak (SCE085): 79 MPH (4:20 PM 08/20)|Silverwood Lake (SCE1424): 75 MPH (10:40 PM 08/20)|Burns Canyon: 71 MPH (5:51 PM 08/20)|Cajon Lookout (SCE338): 65 MPH (11:00 PM 08/20)|Snow Peak (SCE1045): 62 MPH (5:00 PM 08/20)|Banning RAWS: 61 MPH (5:13 PM 08/20)|Waterman Cyn 2 (SCE623): 61 MPH (9:50 PM 08/20)|Crestline (SCE550): 57 MPH (9:20 PM 08/20)|Pilot Rock (SCE1017): 55 MPH (12:50 AM 08/21)|Edgar Canyon (SCE1158): 54 MPH (4:20 PM 08/20)|Hesperia (SCE358): 54 MPH (1030 PM 08/20)|Lake Arrowhead (SCE798): 54 MPH (10:00 PM 08/20)|Hesperia South (SCE1061): 53 MPH (12:30 AM 08/21)|Panorama Point (SCE1106): 53 MPH (9:50 PM 08/20)|Running Springs (SCE1221): 53 MPH (9:30 PM 08/20)|Phelan (SCE336): 53 MPH (1:20 AM 08/21)|Banning (SCE670): 53 MPH (4:00 PM 08/20)|Lake Arrowhead (SCE342): 52 MPH (9:20 PM 08/20)|Crestline (SCE359): 52 MPH (11:10 PM 08/20)|Lake Arrowhead (SCE364): 52 MPH (9:40 PM 08/20)|Crestline (SCE653): 52 MPH (10:20 PM 08/20)|Lake Arrowhead (SCE742): 52 MPH (9:40 PM 08/20)|Wildwood Cyn (SCE1159): 51 MPH (9:10 AM 08/20)|Oak Glen (SCE1088): 50 MPH (5:00 PM 08/20)|Marshall Peak (SDHGPA): 50 MPH (10:30 PM 08/20)|Skyforest Hwy 18 (SCE357): 50 MPH (10:30 PM 08/20).

A tree was downed southeast of Big Bear Lake, blocking lanes of a highway.

Flood, Riverside

When: August 20, 8:00 AM PST to 10:00 AM PST
Where: Riverside County, 1.19 mi NNE of Cathedral City to 1.28 mi NE of Cathedral City
Cause: Heavy Rain / Tropical System
Reported by: Broadcast Media
Coordinates: 33.785, -116.459

Fourteen residents at an assisted living facility were rescued by bucket loaders when mud and water over a foot deep surrounded their homes on Date Palm Drive in Cathedral City.

Flood, San Diego

When: August 20, 10:00 AM PST to 12:00 PM PST
Where: San Diego County, 2.15 mi SSW of Mountain Spg to 1.46 mi SSW of Mountain Spg
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 32.640, -116.110

Debris, rocks, and mud reported on In Ko Pah Road.

Flash Flood, San Bernardino

When: August 20, 11:30 AM PST to 1:30 PM PST
Where: San Bernardino County, 1.75 mi NE of Wrightwood to 2.28 mi NNE of Wrightwood
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 34.370, -117.612

Video received from this area near Sheep Creek showing boulders, rocks, and high water over State Highway 2 after 6.23 inches of rain fell. Time is estimated.

Flash Flood, Riverside

When: August 20, 12:00 PM PST to 2:00 PM PST
Where: Riverside County, 0.81 mi E of Owl to 1.6 mi NE of Cabazon
Cause: Heavy Rain / Tropical System
Reported by: Law Enforcement
Coordinates: 33.930, -116.806

Multiple reports of roadway flooding on I-10 in Cabazon.

Flash Flood, San Diego

When: August 20, 12:00 PM PST to 1:30 PM PST
Where: San Diego County, 6.24 mi SSW of Desert Lodge to 6.35 mi SSW of Desert Lodge
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 33.140, -116.380

Highway 78 was washed out at Yaqui Pass.

Tropical Storm, San Diego County Deserts

When: August 20, 12:00 PM PST to 4:00 PM PST
Where: San Diego County Deserts forecast zone
Reported by: Utility Company
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

In Ko Pah (SDGE): 54 MPH (1:30 PM 08/20)|Borrego Valley Airport: 49 MPH (4:15 PM 08/20)|Borrego (SDGE): 43 MPH (4:00 PM 08/20).

A semi trailer was overturned by strong winds in the early evening hours on August 20 near Borrego Springs.

Debris Flow, San Bernardino

When: August 20, 12:00 PM PST to 1:00 PM PST
Where: San Bernardino County, 2.26 mi S of Glen Martin to 1.95 mi NW of Forest Falls
Cause: Heavy Rain / Tropical System
Reported by: Law Enforcement
Coordinates: 34.148, -116.975

Local law enforcement reported debris flows in the Forest Falls and Angelus Oaks areas with rock debris in all lanes. The largest debris flow was estimated to be around 100 yards wide and 6 feet deep.

Flood, San Bernardino

When: August 20, 12:00 PM PST to 7:00 PM PST
Where: San Bernardino County, 1.41 mi SSW of Victorville to 1.27 mi SSW of Victorville
Cause: Heavy Rain / Tropical System
Reported by: Newspaper
Coordinates: 34.512, -117.311

Several streets near Doris Davies Park in Victorville were closed due to flooding.

Flood, San Bernardino

When: August 20, 12:00 PM PST to 7:00 PM PST
Where: San Bernardino County, 1.93 mi NE of Thorn to 1.7 mi SW of Victorville
Cause: Heavy Rain / Tropical System
Reported by: Newspaper
Coordinates: 34.499, -117.326

Reports of street flooding on Park Avenue in Victorville.

Flash Flood, Riverside

When: August 20, 12:51 PM PST to August 21, 1:30 PM PST
Where: Riverside County, 4.12 mi E of Mecca to 4.18 mi WNW of Mortmar
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 33.572, -115.999

A swift water rescue was conducted on Box Canyon Road in Mecca.

Flood, Riverside

When: August 20, 1:00 PM PST to 3:00 PM PST
Where: Riverside County, 1.75 mi NE of Edgemont to 1.6 mi WNW of Sunnymead
Cause: Heavy Rain / Tropical System
Reported by: Law Enforcement
Coordinates: 33.939, -117.260

Local law enforcement reported flooding near Moreno Valley Freeway and Frederick Street.

Flash Flood, Riverside

When: August 20, 1:30 PM PST to 3:30 PM PST
Where: Riverside County, 3.73 mi NNE of Coachella to 3.54 mi E of Indio
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 33.731, -116.158

Two vehicles were stuck in rushing water on Dillon Road and Landfill Road.

Flash Flood, San Bernardino

When: August 20, 2:00 PM PST to 4:00 PM PST
Where: San Bernardino County, 3.02 mi SW of Forest Falls to 3.02 mi ENE of Yucaipa
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 34.054, -116.962

Video received from Potato Canyon in Oak Glen of mud and rocks across the roadway. Mud and rocks surround a residence in Oak Glen following a debris flow. Widespread rocks and mud covers many roadways in the town.

Flood, Riverside

When: August 20, 2:00 PM PST to 4:00 PM PST
Where: Riverside County, 2.21 mi NW of Box Spgs to 2.27 mi NW of Box Spgs
Cause: Heavy Rain / Tropical System
Reported by: Law Enforcement
Coordinates: 33.970, -117.330

Local law enforcement reported flooding at I-215 and MLK Boulevard.

Flash Flood, San Bernardino

When: August 20, 3:00 PM PST to 5:00 PM PST
Where: San Bernardino County, 6.22 mi SSE of Sugarloaf to 6.46 mi SE of Moonridge
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 34.170, -116.780

Portions of State Highway 38 near the Heart Bar Campground were washed out.

Tropical Storm, Coachella Valley

When: August 20, 3:00 PM PST to August 21, 5:30 PM PST
Where: Coachella Valley forecast zone
Reported by: Utility Company
Coordinates: 33.744, -115.994 (the zone’s center; the record gives no point)

Tropical Storm Hilary produced widespread tropical storm-force winds across Southern California on August 20. The following are the top wind gusts reported across the Coachella Valley:

Palm Desert 1: 57 MPH (4:55 PM 08/20)|Palm Springs Tram (SCE361): 57 MPH (5:00 PM 08/20)|Cathedral Canyon: 56 MPH (5:52 PM 08/20)|Mecca: 56 MPH (4:56 PM 08/20)|Palm Springs Airport: 48 MPH (6:27 PM 08/20)|Palm Desert (SCE416): 46 MPH (4:20 PM 08/20)|Palm Springs (SCE638): 46 MPH (5:00 PM 08/20)|I-10 - West Of Date Palm Drive: 44 MPH (4:45 PM 08/20)|Palm Desert: 42 MPH (5:26 PM 08/20)|Indio: 41 MPH (6:15 PM 08/20)|Cathedral City (SCE855): 41 MPH (5:50 PM 08/20).

A large tree was downed in Palm Desert, blocking the eastbound lanes of Route 111, partially closing the road. Other trees were downed along Monterey Ave in Palm Desert. The awning on a Starbucks was downed in Palm Desert.

Flood, Riverside

When: August 20, 3:00 PM PST to 5:00 PM PST
Where: Riverside County, 1.02 mi NNE of Murrieta to 0.99 mi NNE of Murrieta
Cause: Heavy Rain / Tropical System
Reported by: Trained Spotter
Coordinates: 33.563, -117.211

A trained spotter reported flooding in the streets of Old Town Murrieta near the Santa Ana foothills.

Flash Flood, San Bernardino

When: August 20, 4:00 PM PST to 7:00 PM PST
Where: San Bernardino County, 2.82 mi NNE of Seven Oaks to 2.99 mi NNE of Seven Oaks
Cause: Heavy Rain / Tropical System
Reported by: Emergency Manager
Coordinates: 34.190, -116.920

Thirty residents in Seven Oaks were cut off from rescue after the Santa Ana River overflowed and Glass Road was damaged. One person was missing at the time of report, potentially washed into Barton Creek. Seven Oaks Road was closed for Emergency Crews.

Tropical Storm, San Diego County Coastal Areas

When: August 20, 4:00 PM PST to 9:30 PM PST
Where: San Diego County Coastal Areas forecast zone
Reported by: ASOS
Coordinates: 33.028, -116.770 (the zone’s center; the record gives no point)

Tropical Storm, Orange County Inland

When: August 20, 5:00 PM PST to August 21, 12:00 AM PST
Where: Orange County Inland forecast zone
Reported by: Utility Company
Coordinates: 33.677, -117.776 (the zone’s center; the record gives no point)

Tropical Storm Hilary produced widespread tropical storm-force winds across Southern California from early morning on August 20 through the early morning hours on August 21. The following are the top wind gusts reported across Orange County Inland areas:

San Clemente Ridge (SDGE): 57 MPH (6:20 PM 08/20)|San Clemente: 53 MPH (5:55 PM 08/20)|Chino Hills: 52 MPH (6:57 PM 08/20)|Baker Canyon (SCE097): 48 MPH (12:00 AM 08/21)|Chino Hills: 47 MPH (12:08 AM 08/21)|Upper Bell: 47 MPH (6:26 PM 08/20)|Limestone Cyn (SCE1114): 43 MPH (6:50 PM 08/20)|Villa Park Dam (SCE128): 43 MPH (7:20 PM 08/20)|Gypsum Canyon (SCE127): 41 MPH (12:00 AM 08/21).

Trees and large tree branches fell along the Santa Ana river, Riverview Golf Course, and in La Habra. Reports of winds removing shingles from houses in La Habra. 190 customers lost power during the event.

Tropical Storm, Orange County Coastal

When: August 20, 5:00 PM PST to August 21, 12:00 AM PST
Where: Orange County Coastal forecast zone
Reported by: Utility Company
Coordinates: 33.677, -117.776 (the zone’s center; the record gives no point)

Laguna Beach 4 (SE024): 61 MPH (6:50 PM 08/20)|Laguna Niguel 2: 47 MPH (6:50 PM 08/20)|Huntington Beach Pier: 47 MPH (6:52 PM 08/20)|Signal Peak: 45 MPH (12:56 AM 08/21)|Moro Canyon (SCE803): 43 MPH (6:10 PM 08/20)|Newport Pier: 43 MPH (12:16 AM 08/21)|Aliso Viejo (SCE1285): 40 MPH (6:40 PM 08/20)|Moro Cyn Trail (SCE1626): 40 MPH (6:00 PM 08/20).

Tropical Storm, Apple and Lucerne Valleys

When: August 20, 5:00 PM PST to August 21, 3:00 AM PST
Where: Apple and Lucerne Valleys forecast zone
Reported by: Utility Company
Coordinates: 34.841, -116.178 (the zone’s center; the record gives no point)

Tropical Storm Hilary produced widespread tropical storm-force winds across Southern California from August 20 through the early overnight hours into August 21. The following are the top wind gusts reported across the High Desert:

Victorville (7NE): 59 MPH (2:00 AM 08/21)|Hesperia (SCE340): 57 MPH (1:10 AM 08/21)|Hesperia (SCE617): 51 MPH (10:50 PM 08/20)|Phelan (SCE335): 50 MPH (8:00 PM 08/20)|Hesperia South (SCE1037): 49 MPH (10:20 PM 08/20)|Oak Hills (SCE1020): 47 MPH (12:20 AM 08/21)|Burns Canyon Rd (SCE286): 47 MPH (10:00 PM 08/20)|Pioneertown (SCE347): 47 MPH (9:40 PM 08/20)|Phelan (SCE1452): 46 MPH (10:50 PM 08/20)|Lucerne Valley (SCE266): 46 MPH (12:40 AM 08/21).

Flood, Riverside

When: August 20, 11:00 PM PST to August 21, 1:00 AM PST
Where: Riverside County, 1.5 mi NNW of Myoma to 1.38 mi NNW of Myoma
Cause: Heavy Rain / Tropical System
Reported by: Department of Highways
Coordinates: 33.820, -116.330

CalTrans report of roadways near Ramon Road and Thousand Palms Canyon Road completely submerged.

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.
Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.
Tropical Storm: A tropical cyclone with sustained winds of 34 to 63 knots (39 to 73 mph).
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 California in 2023 Every state in 2023 This day in weather history Warnings in California, August 2023 The 2023 hurricane season

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 2026-10-01. Each event’s entry at NCEI: 1133187, 1133235, 1133240, 1133251, 1129806, 1129807, 1129810, 1129836, 1129865, 1133518, 1129863, 1129866, 1129871, 1129864, 1129869, 1129870, 1132564, 1129837, 1129824, 1129816, 1129834, 1129867, 1133512, 1133520, 1133521, 1129813, 1132569, 1129817, 1129825, 1132567, 1129829, 1129874, 1132566, 1129832, 1129868, 1129872, 1129873, 1129875, 1132565.