Arizona flood risk is expected to rise over Halloween weekend as tropical moisture combines with a developing weather system, bringing showers, thunderstorms and periods of heavy rain from Friday 30 October into Sunday 1 November.
Phoenix will remain warm and dry for the next few days, with temperatures reaching about 86F (30C) on Tuesday 27 October. Highs should stay in the mid to upper 80s on Wednesday and Thursday, although increasing cloud will signal the change ahead.
The National Weather Service has warned that unsettled conditions are likely to return across the state late in the week, with the greatest chances of rain expected on Friday and Sunday.
Arizona flood risk Halloween weekend
A disturbance moving through the region on Friday will interact with a larger trough forming along the West Coast. Moisture drawn northwards from the south, including remnants of Tropical Storm Vance, is expected to fuel scattered showers and thunderstorms.
Forecasters do not expect the severe weather threat to be as intense as the storms seen in Arizona the previous week. However, heavier bands of rain could cause flooding, particularly across central, southern and eastern parts of the state.
Vance was weakening over the eastern Pacific on Tuesday and was forecast by the US National Hurricane Center to become a post-tropical system by Friday. Even as the storm loses its tropical characteristics, moisture associated with it could still be drawn into the wider weather pattern affecting Arizona.
Rain may ease on Saturday morning, with many areas becoming temporarily drier during the day. Showers could linger over higher ground during the afternoon and early evening on Halloween, before another area of wet weather begins moving into the state later that night.
Sunday is expected to bring the most widespread spell of rain. A trough and low-pressure centre approaching from the north will combine with another disturbance from the south-west, creating conditions for steady rainfall and isolated thunderstorms. The main concern is expected to be flooding rather than severe storms.
Temperatures will fall as cloud and moisture increase, with highs of about 76F (24C) on Friday, 77F (25C) on Halloween and 72F (22C) on Sunday. Milder conditions in the mid to upper 70s are expected to continue into next week as Arizona gradually dries out.
Drivers have been urged to avoid flooded roads and never attempt to cross moving or standing water. Anyone who encounters rapidly rising water should leave their vehicle and move to higher ground, while residents in flood-prone areas should be prepared to follow evacuation instructions.
