Flood — Pima, Arizona

2018-10-02 to 2018-10-03 · near Ali Chuk, Pima, Arizona

Event narrative

Widespread heavy rain of 2 to 4 inches with isolated amounts of 5 to 8 inches fell mainly from the evening of October 1st through the morning hours of October 2nd. Runoff from this rainfall continued through the night of the 2nd, with the peak flows generally during the afternoon. Several roads, including Indian Routes 1, 15, 21, 23, 34, and 45, as well as sections of Highway 86 became, or continued to be, impassable on the Tohono O'odham Nation. Several of these roads sustained significant damage. Homes that were flooded earlier in the morning from flash flooding remained flooded or saw water levels rise. Additional homes were flooded by continued runoff during the afternoon. At least 50 homes were flooded in the following districts: Gu Vo (11); Pisinemo (17); Sif Oidak (20); and Hickiwan (2). Several dozen residents were evacuated from their homes. At least 20 earthen dams and levees were damaged along with the tribal water and utility system infrastructure. Runoff nearly filled Menagers Lake, prompting fears of a dam failure and the evacuation of the village of Ali Chugk.

Wider weather episode

What was Major Hurricane Rosa crossed the northern Baja peninsula as a tropical depression October 1st. The remnant circulation entered southwest Arizona on October 2nd. Moisture ahead of these remnants fueled thunderstorms in southeast Arizona on September 30th. Rain associated with the remnant circulation moved northeast across southeast Arizona through October 2nd. The primary period of heavy rain occurred from 8 pm MST October 1st through 8 am MST October 2nd. Rainfall totals averaged two to four inches on the west half of the Tohono O'odham Nation with isolated heavier amounts of five to eight inches. The heavy rain initially resulted in flash flooding, but evolved into a longer term period of flooding which led to evacuations of several villages, road closures, considerable infrastructure damage, and a subsequent disaster declaration.

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Source: NOAA Storm Events Database, event_id 788373. Narrative written by the NWS forecast office that issued the report.