Phoenix is forecast to reach about 101 degrees Monday afternoon after starting the day in the low 80s.
The heat will build quickly through the morning, with temperatures reaching the upper 90s around midday. Winds are expected to remain light from the southeast, though some afternoon gusts could reach the mid to upper teens. Monday night should be mostly clear, with a low near 78.
Heat briefly eases before storm chances return
Tuesday is expected to remain sunny with a high near 99 degrees. A slight chance of showers and thunderstorms returns Wednesday evening and continues Thursday, when highs should be near 97. The forecast calls for another sunny day near 98 Friday, a hotter Saturday near 104 and a Sunday high near 98 with a slight afternoon storm chance.
Those projections describe a hot late-September stretch, but Monday’s forecast is not close to Phoenix’s daily record. The National Weather Service lists the normal high for Sept. 21 as 99 degrees and the record as 107, set in 2001, 2003 and 2011.
Why a day without a warning can still matter
A forecast just above normal does not by itself establish an unusual or dangerous event, and the current forecast does not prove that Monday will produce heat illness. But official health data shows why residents should not treat formal warnings as the only marker of risk. The Maricopa County Department of Public Health recorded 430 heat-related deaths in 2025.
The county report also found that 42% of those deaths occurred during periods when an excessive heat warning was in effect. The National Weather Service issued five such warnings totaling 31 days in 2025, meaning a majority of the recorded deaths occurred outside those warning periods. That comparison is historical countywide data, not a prediction about Monday.
The National Weather Service Phoenix office says CDC-collaborative research has found that heat-associated deaths in Arizona can occur when temperatures are in the mid-80s or hotter. Its HeatRisk product evaluates temperatures relative to normal, the duration of unusual heat and humidity, including overnight lows, rather than relying only on the afternoon high.
Recent heat has been persistent
The broader climate backdrop has also been warm: the National Weather Service Phoenix climate summary said 2025 was the second-warmest year recorded in Phoenix. The year included 122 days at or above 100 degrees and 37 days at or above 110 degrees. Those figures provide recent context for another triple-digit forecast, but they do not establish a trend in Monday’s health impacts.
Where to find relief
People who need a cooler place can use City of Phoenix cooling centers, which the city says are free, open to all community members and do not require identification. The city’s Heat Relief Network also offers free water and indoor locations for cooling off.
For outdoor work or exercise, the practical response to Monday’s heat is to choose cooler morning or evening hours, drink water regularly and take breaks in shade or air conditioning. The forecast remains subject to change, especially for the midweek storm chances.
