Flood Watch issued across Southern Arizona ahead of early week storms

Residents across Tucson and Southern Arizona should prepare for a period of heavier rain, thunderstorms and possible flash flooding beginning Monday. The National Weather Service has issued a Flood Watch for all of Southeast Arizona from 11 a.m. Monday through 11 p.m. Tuesday. For people commuting, working outdoors, hiking or traveling through normally dry washes, the greatest concern will be rapidly changing conditions and localized flooding, especially Monday night and Tuesday.

The weather pattern is expected to become more active as a low pressure system moves in from the west and tropical moisture associated with Hurricane Polo surges north from the south. That combination will increase humidity and storm coverage across the region. Rain chances in the Tucson metropolitan area are expected to reach 80 percent Monday night and remain at 80 percent Tuesday. Forecasters identify heavy rain and localized flash flooding as the primary threats, with the most active conditions likely affecting both the morning and evening commutes Tuesday.

Before the storm system arrives, Tucson will see partly cloudy skies and mild to warm temperatures. Sunday’s high is expected to reach about 94 degrees, with a low near 72 and only a 10 percent chance of rain. Monday will be somewhat cooler, with a high near 89 and a 40 percent chance of showers and thunderstorms. The likelihood of rain increases sharply Monday night, when temperatures fall to around 70 and storms become more widespread.

Tuesday is expected to bring partly sunny skies, an 80 percent chance of showers and thunderstorms, and a high near 82 degrees. Rain chances decrease to 40 percent Tuesday night and 20 percent Wednesday, although scattered storms remain possible. Overnight temperatures will settle into the 60s and low 70s, including a forecast low near 63 Tuesday night and near 64 Wednesday night. Drier conditions should return later in the week, with temperatures warming back into the low 90s by the end of the workweek.

The Southern Arizona forecast is part of a broader period of unsettled weather across Arizona. Storms, rising humidity, high winds, blowing dust and flash flooding have also been forecast in central and northern portions of the state. Mountain storms are expected to track southwest, increasing the potential for rain across Arizona. Damaging wind gusts and hail are possible in stronger storms, and areas that receive repeated rounds of rainfall could see flooding develop quickly.

Recent storm activity in the high country has already produced flash flood warnings, flood advisories and severe storms. Storms have been moving southwest from the mountains during evening and overnight hours, a pattern that can send rain into communities far from where a storm first forms. While storm chances were expected to become more scattered or isolated later in the week and into the weekend, the broader forecast still included some chance of storms into the following week. In central Arizona, cooler weekend temperatures in the upper 90s were expected to be offset by high humidity, making conditions feel closer to the low 100s.

For Tucson residents, the most important safety reminder is to avoid flooded roads and washes. Drivers should never attempt to cross a roadway covered by moving water, even if the water appears shallow. The recommended response is to turn around and choose another route. If water begins rising around a vehicle, occupants should get out quickly and move to higher ground, when it is safe to do so. Officials and emergency organizations also advise residents to monitor local radio, NOAA weather information and other reliable updates, particularly during the Flood Watch period.

People in flood-prone neighborhoods should be ready to leave quickly if conditions worsen or evacuation instructions are issued. Downed power lines can energize nearby ground and standing water, so residents should stay away from both. If the power goes out, use flashlights rather than candles or other open flames. Households are encouraged to keep extra batteries, a first aid kit, drinking water and food that does not require refrigeration or cooking. Those who depend on electricity for medical equipment should arrange backup power, and residents should have a way to keep cellphones charged.

The storms will arrive after a stretch of dangerous heat in other parts of Arizona, so heat safety remains important even as temperatures cool. Health officials recommend drinking water before, during and after outdoor work or exercise, limiting strenuous activity during the hottest part of the day and checking on older adults and other people at risk of heat illness. Anyone hiking or exercising outdoors should carry a cellphone, tell someone where they are going and avoid going alone when possible. The changing forecast makes it especially important to check conditions before leaving home and to remain alert for new warnings through Tuesday.