After the rain ended, the Santa Cruz, Rillito, and Gila rivers experienced their highest crests on record.

President Ronald Reagan declared Cochise, Gila, Graham, Greenlee, Pima, Pinal, Santa Cruz and Yavapai counties a "major disaster area".

Well before the start of the rainfall, much of Arizona had been affected by a wet winter and subsequent monsoon season leaving the grounds saturated and susceptible to flooding.

A thermal low lay over the mouth of the Gulf of California while the tail end of a weak cold front was located atop of the Great Basin.

[2] On September 28, moisture from the storm began spreading across Mexico and the southwest United States, due to a stalled low pressure area off the coast of California drawing the thunderstorms northeastward.

[1] Tropical Storm Octave played a vital role in the disaster by supplying warm, moisture to the region, which collided with cooler air from the subtropics.

Steered by a deep layer high over Mexico, the disturbance moved west for four days before attaining tropical depression status.

Upon becoming a tropical cyclone the depression was situated over warm waters; however, wind shear subsequently increased in the vicinity of the storm.

Therefore, significant development was impeded as the depression curved back to the north along an adjacent upper-level low.

[4] As conditions aloft turned favorable by September 28, the depression strengthened into Tropical Storm Octave at 1800 UTC that day.

Within six hours, Octave attained its peak intensity of 50 mph (80 km/h) and decreased in forward speed while turning to the northeast.

Consequently, the winds gradually decreased to 35 mph (55 km/h) and the storm was downgraded back to tropical depression status during the afternoon.

[5] At 1200 UTC on October 2, the EPHC issued their last advisory on the storm as the surface circulation had dissipated.

The Pima County Emergency Services Director stated that "we just didn't see the need for activating the EBS system."

Despite the lack of EBS broadcasts, NOAA Weather Radio claims it did the best it could to provide updated information on Octave.

[1][17] Already inundated by previous rains, additional rainfall moved over the area; much of the state of Arizona was deluged with 6 in (150 mm) of precipitation in a mere two days.

[20] In Tucson, flood waters reportedly reached 8 ft (2.4 m), stranding hundreds of people on rooftops.

[24] After a third bout of heavy rain on October 2, the Santa Cruz, Rillito, and Gila rivers experienced their highest crests on record.

[1] A flow rate of 25,000 cu ft (707,921,165 cc) per second was measured in the Rillito river;[18] the Santa Cruz river peaked at a flow rate of 1,490 m3 (52,620 cu ft),[2] which was short of the record set during Hurricane Heather during the 1977 Pacific hurricane season.

[25] All other rivers that pass through Tucson did not attain record levels and were significantly lower than past flood episodes.

Additionally, communities along the Santa Cruz River were flooded, forcing 4,000 residents to evacuate their homes, many of whom lost key property possessions.

[18] Tropical Storm Octave also caused major flooding along the Gila River,[2] which reached its highest discharge rates since 1906.

[25] In Willcox, a farming community 80 mi (130 km) east of Tucson, residents armed with shovels and sandbags fought rising floodwaters after the Hooker Dam, an earthen dam 35 mi (55 km) north of Willcox, burst, preventing further destruction.

A relief helicopter crashed in attempt to rescue a woman and her baby, killing its two crew members.

[39] President Ronald Reagan declared Arizona counties Cochise, Gila, Graham, Greenlee, Pima, Pinal, Santa Cruz and Yavapai a "major disaster area" on October 5.

[24] Many workers from dozens of companies used cranes, dynamite, trucks, and hammers to clean up dried 7 ft (2.1 m) mud near some rivers.