Arizona was facing an elevated flash-flood risk as heavy rain linked to tropical moisture and an approaching Pacific weather system spread across the state, with areas east of Phoenix considered particularly vulnerable.
The National Weather Service issued flood watches across much of Arizona on Monday 28 September, warning that showers and thunderstorms could continue through Tuesday evening. Forecasters said rainfall totals could range from half an inch to as much as two inches in some areas.
Gabriel Lojero, a meteorologist with the National Weather Service in Phoenix, said moisture from the remnants of Hurricane Odalys and Hurricane Polo was combining with a system moving towards the West Coast. Polo was expected to make landfall in Baja California later on Monday.
Flood risk east of Phoenix
The National Weather Service said moderate to heavy rain could fall at rates of more than an inch an hour, with repeated storms potentially producing higher accumulations. The greatest concern was focused on higher ground and foothill areas in central and eastern Arizona, including parts of Maricopa, Pinal and Gila counties.
Maricopa County’s Flood Control District said rainfall would be welcome after a prolonged dry spell, but warned that parched ground could increase surface run-off. Brian Hurley, a senior national forecaster, said the soil could become “hydrophobic”, causing water to run off rather than soak into the ground.
“Any time you see heavy rainfall in such a short amount of time, especially those areas that get the majority of activity are going to be at the greatest risk for flash flooding,” Mr Lojero said.
The National Weather Service said parts of south-east Arizona could receive between one and two inches of rain, with two to four inches possible across some higher terrain, including the Sky Islands and White Mountains.
Residents in flood-prone locations were advised to monitor warnings and prepare to move to safer ground if necessary. The City of Phoenix made sand available at designated parks, while Mesa listed locations where residents could obtain free sand and bags.
Kim McMahon, a public information officer for the Flood Control District of Maricopa County, advised residents to fill sandbags only halfway to three-quarters full and stack them in a brick pattern, concentrating on doors, garage entrances and other low points where water could enter.
The storm was expected to move away from the region by Wednesday, bringing a return to drier conditions.
