The month picked up where August left off, with an active monsoon pattern bringing periods of showers and thunderstorms to the mountains and deserts. The storms were confined to the deserts where intense isolated strong/severe thunderstorms on the 7th, 8th and 9th produced damage and impacts. Flash flooding was especially intense in Palm Springs and Cathedral City on the 9th, where structures throughout the city were flooded and roads were covered in debris. At Palm Springs High School 31 classrooms were inundated. Major flood damage also occurred at the Safari Mobile Home Park. Palm Springs set a daily record with 1.19 inches of rainfall. Many trees were toppled on September 8th when 62 mph winds occurred at Thermal Airport.

Thunderstorm Wind in SAN DIEGO, CALIFORNIA
From 08-SEP-17 17:30:00 to 08-SEP-17 18:00:00 (PST-8)
Location: OCOTILLO WELLS
Magnitude: 52.00 EG
Reported by: Law Enforcement

A state park ranger reported strong outflow winds from a thunderstorm with estimate peak gusts of 60 mph.

Flash Flood in SAN DIEGO, CALIFORNIA
From 07-SEP-17 17:00:00 to 07-SEP-17 19:00:00 (PST-8)
Location: OCOTILLO WELLS
Flood cause: Heavy Rain
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A state park ranger reported water up to 6 feet deep and 100 yards wide near the intersection of Salt Wash and Cutacross Trail. An additional photo from twitter showed minor road damage at Highway 78 and Fault Wash near Ocotillo Wells.

Thunderstorm Wind in RIVERSIDE, CALIFORNIA
From 08-SEP-17 17:15:00 to 08-SEP-17 18:00:00 (PST-8)
Location: (TRM)THERMAL ARPT
Magnitude: 54.00 MG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: ASOS

The ASOS at Jacqueline Cochran Regional Airport in Palm Springs reported a 62 mph wind gust between 1740 and 1746 PST. Multiple large trees and a fence were also toppled near the airport. Radar indicated the potential for additional severe gusts between 1730 and 1800 PST.

Flash Flood in SAN DIEGO, CALIFORNIA
From 09-SEP-17 15:00:00 to 09-SEP-17 16:30:00 (PST-8)
Location: BORREGO SPGS
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

A mix of water and debris flowing through the normally dry Coyote Wash was reported around 1500 PST, by 1515 PST several inches of water and debris were flowing near Canyon Entrance dirt road and the Citrus Groves.

Lightning in SAN DIEGO, CALIFORNIA
From 09-SEP-17 06:00:00 to 09-SEP-17 06:00:00 (PST-8)
Location: WARNER SPGS
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A lightning strike knocked out power to 1000 customers in Palm Springs.

Flash Flood in RIVERSIDE, CALIFORNIA
From 09-SEP-17 16:15:00 to 09-SEP-17 18:15:00 (PST-8)
Location: PALM SPGS
Flood cause: Heavy Rain
Property damage: 1.00M
Crop damage: 0.00K
Reported by: Broadcast Media

The second intense thunderstorm of the day rolled over Palm Canyon and Palm Springs producing a daily rainfall record. Intense runoff through Palm Canyon Creek and the Whitewater River resulted in a closure of Cathedral Canyon Road and a swiftwater rescue and closure at Golf Club Drive. South Araby Drive was also closed. Other sections of the city were inundated with standing water and street flooding. Numerous homes suffered flood damage, cars were water logged and streets covered in debris.

Flash Flood in SAN DIEGO, CALIFORNIA
From 07-SEP-17 18:15:00 to 07-SEP-17 18:45:00 (PST-8)
Location: DESERT LODGE
Flood cause: Heavy Rain
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Public

Flash flooding washed out the shoulder of the S22 (Borrego Salton Seaway) near Borrego Springs.

Flash Flood in RIVERSIDE, CALIFORNIA
From 09-SEP-17 16:00:00 to 09-SEP-17 18:00:00 (PST-8)
Location: (PSP)PALM SPGS ARPT
Flood cause: Heavy Rain
Property damage: 400.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A 1-3 ft wall of water and debris surged through the Safari Mobile Home Park in Palm Springs. Multiple homes were damaged, Santa Monica Street was filled with debris and several residents were stranded in their homes.

Flash Flood in RIVERSIDE, CALIFORNIA
From 09-SEP-17 16:00:00 to 09-SEP-17 18:00:00 (PST-8)
Location: (PSP)PALM SPGS ARPT
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Palm Springs High School suffered major flood damage for the second time in a month. A total of 31 classrooms were flooded.

Thunderstorm Wind in RIVERSIDE, CALIFORNIA
From 09-SEP-17 15:45:00 to 09-SEP-17 16:15:00 (PST-8)
Location: PALM SPGS
Magnitude: 48.00 MG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: ASOS

Strong downburst winds from a thunderstorm produced a 55 mph wind gust at Palm Springs International Airport. Winds may have been stronger elsewhere in the city. Southern California Edison reported 1000 power outages.

Thunderstorm Wind in RIVERSIDE, CALIFORNIA
From 07-SEP-17 15:50:00 to 07-SEP-17 16:20:00 (PST-8)
Location: THOUSAND PALMS
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Downburst winds from a thunderstorm toppled several trees at the Children's Discovery Museum in Rancho Mirage, CA, the irrigation system was also damaged.

Lightning in RIVERSIDE, CALIFORNIA
From 07-SEP-17 16:00:00 to 07-SEP-17 16:00:00 (PST-8)
Location: PALM DESERT
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

A lightning strike struck a palm tree, catching the tree and a residence on fire.