The monsoon high broke down over Arizona late in August with a trough setting up over the southwest U.S. leading to southwest flow over the state. Tropical moisture was able to push up the Gulf of California into Arizona under this setup. This prompted a Flash Flood Watch for the central and southern Arizona deserts for the 29th and 30th. With well above normal moisture levels, training of storms and high rain rates were able to produce flash flooding in the afternoon and evening hours of both days. The highest rainfall totals were in southeast reaches of the Phoenix metro area on the 29th with a cluster of storms and in northwest Maricopa county on the 30th with a nearly stationary line of storms. A few storms on both days also produced damaging winds.

Thunderstorm Wind in MARICOPA, ARIZONA
From 29-AUG-20 19:46:00 to 29-AUG-20 19:46:00 (MST-7)
Location: NORTON
Magnitude: 52.00 EG
Property damage: 15.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorms, some with gusty and damaging outflow winds, developed across western portions of the greater Phoenix area during the evening hours on August 29. Some of the stronger storms affected the community of Goodyear.  According to a trained weather spotter located 6 miles south of Goodyear, at 1946MST gusty winds estimated to be at least 60 mph in strength blew down many trees across Estrella Parkway, just south of the Gila river and north of the Golf Club of Estrella. There were no reports of injury due to the falling trees.

Flash Flood in MARICOPA, ARIZONA
From 30-AUG-20 20:00:00 to 30-AUG-20 23:15:00 (MST-7)
Location: TONOPAH
Flood cause: Heavy Rain
Property damage: 2.00K
Crop damage: 0.00K
Reported by: Department of Highways

Thunderstorms with heavy rain developed across the central deserts well to the northwest of Phoenix during the evening hours on August 30th. Heavy rain, with peak rain rates in excess of one inch per hour, led to episodes of flash flooding about 12 miles to the northeast of Tonopah. According to data from a Maricopa County Flood Control District rain gage, Jackrabbit Wash crested at the 3.1 foot stage with a flow of 784 cubic feet per second. The resulting flood wave resulted in Wickenburg/Aguila road becoming flooded as 1.5 feet of water flowed through the wash and across the road. The flooding took place at about 2200MST. A flash flood watch was in effect at the time of the flooding. There were no reports of accidents or injury due to the flooded road.

Flash Flood in MARICOPA, ARIZONA
From 29-AUG-20 19:45:00 to 29-AUG-20 23:00:00 (MST-7)
Location: LIBERTY
Flood cause: Heavy Rain
Property damage: 40.00K
Crop damage: 0.00K
Reported by: Fire Department/Rescue

Thunderstorms with heavy rain developed across western portions of the greater Phoenix area during the evening hours on August 29; some of the stronger storms affected the areas around the community of Buckeye. According to the Buckeye Valley fire department and rescue units, at 2003MST deputies responded to a SUV with a family of five that was stuck in a flooded wash in the Buckeye Valley. The SUV was stuck near the intersection of Tuthill and Carla Vista Roads. Fortunately, the family was removed by bystanders. A Flash Flood Watch was in effect at the time of the rescue.

Flash Flood in MARICOPA, ARIZONA
From 30-AUG-20 15:30:00 to 30-AUG-20 19:45:00 (MST-7)
Location: ESTRELLA
Flood cause: Heavy Rain
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Public

Thunderstorms, some with locally heavy rain, developed over the central deserts during the afternoon hours on August 30th. Some of the stronger storms formed to the southwest of Phoenix, producing heavy rain along Highway 238 to the southwest of the town of Mobile. Peak rain rates were in excess of one inch per hour, leading to episodes of flash flooding. According to a social media report from the public, at about 1630MST flash flooding 10 miles southwest of Mobile stranded 3 vehicles in flood waters along Highway 238. At about the same time, the Arizona Department of Transportation reported that flash flooding southwest of Mobile resulted in the closure of State Route 238 between mileposts 25 and 28. There were no reports of accidents or injury due to the flash flooding. A Flash Flood Watch was in effect during the flash flooding episodes.

Flash Flood in GILA, ARIZONA
From 30-AUG-20 00:15:00 to 30-AUG-20 04:10:00 (MST-7)
Location: JAKES CORNER
Flood cause: Heavy Rain / Burn Area
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Utility Company

Thunderstorms with locally heavy rain developed across the high terrain northeast of Phoenix during the very early morning hours on August 30th. The heavy rain led to flash flooding across portions of the Bush burn scar near the town of Sunflower. As an example of the heavy rain, a rain gage at Mount Ord measured just over one inch during the one hour period ending at 0134MST. According to the local utility company, Salt River Project, at 0140MST flash flooding caused a 3 foot rise along Slate Creek at the US Forest Road number 26 crossing, about 7 miles northeast of Sunflower. A short distance downstream they estimated a 7 foot rise in the creek based on high water marks on the local vegetation. There were no reports of accidents or injury due to the flash flooding.

Flash Flood in MARICOPA, ARIZONA
From 30-AUG-20 19:00:00 to 30-AUG-20 23:15:00 (MST-7)
Location: TONOPAH
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Department of Highways

Thunderstorms with heavy rain developed across the central deserts and well to the northwest of Phoenix during the evening hours on August 30th. Peak rain rates in excess of 1 inch per hour led to flash flooding and one such episode occurred near the Maricopa and La Paz County line. According to the Arizona Department of Highways, flash flooding just east of the county line resulted in the closure of Eagle Eye road from Salome Road to US Highway 60 in Aguila. The road was reported closed as of 2200MST although heavy rain and flooding most likely were occurring earlier than that. There was a flash flood watch in effect at the time of the flash flooding.

Thunderstorm Wind in MARICOPA, ARIZONA
From 29-AUG-20 19:40:00 to 29-AUG-20 20:00:00 (MST-7)
Location: CHANDLER ARPT
Magnitude: 56.00 EG
Property damage: 20.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorms with gusty and damaging outflow winds developed over the southeast portions of the greater Phoenix area during the evening hours on August 29. Some of the stronger storms developed near the community of Sun Lakes. According to a trained weather spotter located 4 miles east of Sun Lakes, at 1940MST outflow winds estimated to be at least 65 mph in strength uprooted a large tree with a diameter of 18 inches. The tree fell on a house near the intersection of Alma School and Riggs Roads. No injuries were reported. A bit later, at 2000MST, another trained spotter reported that strong winds snapped a tree with a diameter of 5 inches about 6 miles northeast of Sun Lakes. Numerous branches were also stripped from the trees.

Thunderstorm Wind in LA PAZ, ARIZONA
From 30-AUG-20 19:45:00 to 30-AUG-20 19:45:00 (MST-7)
Location: VICKSBURG
Magnitude: 52.00 EG
Property damage: 30.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Isolated thunderstorms developed across portions of La Paz County during the early evening hours on August 30th; some of the storms generated gusty and damaging outflow winds. According to a local emergency manager, at 1945MST wind gusts estimated to be as high as 60 mph downed multiple power poles about 2 miles to the southwest of the town of Vicksburg. There were no injuries reported.

Thunderstorm Wind in MARICOPA, ARIZONA
From 29-AUG-20 12:02:00 to 29-AUG-20 12:02:00 (MST-7)
Location: SUN CITY
Magnitude: 43.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Isolated strong storms moved through northwest Phoenix around midday. Tree damage from thunderstorm downburst wind gusts was reported by a trained spotter driving on Loop-101.  Various sized tree limbs were blown over onto parts of the Loop-101 southbound and adjacent business parking lots near Bell road. The spotter also reported a few cars on Loop-101 may have struck the tree debris and that Peoria Police Department was on the scene. No official damages were reported and no injuries were reported.

Thunderstorm Wind in MARICOPA, ARIZONA
From 29-AUG-20 19:28:00 to 29-AUG-20 19:28:00 (MST-7)
Location: OCOTILLO
Magnitude: 48.00 EG
Property damage: 5.00K
Crop damage: 0.00K
Reported by: Trained Spotter

A large tree, 18 inches in diameter became uprooted by strong thunderstorm winds and fell on a house in south Chandler near Alma School road and Riggs road. Winds were estimated around 50-55 mph based on radar and nearby weather station. No injuries were reported.

Thunderstorm Wind in MARICOPA, ARIZONA
From 29-AUG-20 19:30:00 to 29-AUG-20 19:45:00 (MST-7)
Location: LIBERTY
Magnitude: 52.00 EG
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorms, some with gusty and damaging wind, developed across western portions of the greater Phoenix area during the evening hours on August 29. Some of the stronger storms affected the community of Goodyear. According to a trained weather spotter located 8 miles south of Goodyear, at 1930MST winds estimated to be as high as 60 mph downed about 6 trees with diameters of up to 6 inches. Dozens of smaller branches around 1 inch across were also downed. Shortly after that, at 1945MST, the spotter indicated that some concrete roof tiles were stripped off of a section of a house rooftop. Additionally, a large Palo Verde tree was heavily damaged. There were no reports of injuries due to the strong wind.