New York City Mayor Zohran Mamdani has sparked strong reactions in the United States after urging residents to set their air conditioners to 25.5°C, or 78°F, as a dangerous and prolonged heatwave grips much of the eastern part of the country.

The recommendation, intended to ease pressure on the city’s power grid, has drawn criticism from citizens and commentators who argue that it does not reflect the severity of the conditions. In New York, the heat index is expected to reach around 43°C, while in parts of the surrounding suburbs it could climb as high as 46°C.

Mamdani had warned that the city was facing “one of the most extreme heatwaves of the past 10 years”, raising concerns over public health, energy demand and the resilience of urban infrastructure.

Daily life in Manhattan has already been disrupted, with residents adjusting their routines to avoid the worst of the heat. One 22-year-old college student described rushing to walk her dog early in the day, before temperatures became unbearable.

Although most buildings in the United States have air conditioning, extreme heat remains one of the country’s deadliest weather-related hazards, often claiming more lives than hurricanes or floods. Authorities are particularly concerned about the duration of the heatwave, as sustained high temperatures, humidity and warm nights can place serious strain on elderly people, outdoor workers, low-income households, tourists and others at greater risk.

The heat is also testing infrastructure. New York weather officials have warned of possible disruption to power and water supplies as electricity demand surges. In Chicago, power provider ComEd said the grid was under “extreme strain” and urged residents to reduce energy use where possible.

Across the country, millions of Americans are facing sweltering conditions expected to last for several days, affecting cities including Washington, D.C., as well as major public gatherings linked to the World Cup and events marking the 250th anniversary of the U.S. Declaration of Independence.

The National Weather Service has described the heatwave as dangerous and potentially record-breaking, warning that high humidity will make conditions feel even hotter. Forecasters expect the system to continue affecting much of the central and eastern United States before shifting further towards the East Coast over the weekend.