Arizona faced a sharp shift from oppressive heat to a heightened risk of thunderstorms and flash flooding, with storms developing across the state on Monday evening and further rain expected through Wednesday, 16 September.
Phoenix reached 105F (40.6C) on Monday, while the overnight low remained at 89F (31.7C) — a record-warm morning minimum. The hot and humid conditions were followed by isolated showers and thunderstorms in and around the Valley, including near Maricopa and Casa Grande.
Rain was expected to continue overnight across southern and eastern Arizona, with showers and thunderstorms forecast to persist into Tuesday morning. The National Weather Service said the main concern over the coming days would be heavy rainfall and localised flash flooding, particularly in higher terrain and areas north and east of Phoenix.
Flash flooding risk increases across Arizona
Tuesday, 15 September, was expected to be mostly dry and partly sunny in much of the state, although isolated storms could return during the afternoon and evening in eastern Arizona and later across other areas.
Forecasters warned that the greatest risk of flash flooding would be in the south-eastern part of Arizona, where storms could produce intense rainfall over a short period. The threat was expected to increase from Tuesday night into Wednesday as a disturbance pushed additional moisture northwards through the state.
Temperatures were forecast to ease slightly during the wetter period, with highs in the mid to upper 90s on Wednesday if cloud and rain became more widespread. Conditions were then expected to turn drier from Thursday, before temperatures climbed back towards the low 100s over the weekend.
Residents in flood-prone areas were urged to avoid driving through standing or flowing water. Officials reiterated that motorists should turn around rather than attempt to cross a flooded road, while people caught by rapidly rising water should leave their vehicles and move to higher ground.
Despite the incoming storms, heat-related risks remained significant. People were advised to stay hydrated, limit strenuous outdoor activity during the hottest part of the day and check on vulnerable friends, relatives and neighbours.
