A weeklong heat wave that officials believe has killed at least 25 people continued Sunday, with 40 million people under heat alerts across the East Coast, Southeast and Southwest.Limited time: Save 25% on NBC News subscriptionGet exclusive reporting, live Q&As and ad-free reading.At least 18 record highs were set on the Fourth of July as celebrations kicked off in cities including Washington, D.C.; Baltimore; Raleigh, North Carolina; Norfolk, Virginia; and Atlantic City, New Jersey.A young visitor shields themself from the sun during July Fourth celebrations in Washington, D.C., on Saturday.Finn Gomez / Getty ImagesOn Sunday, alerts will continue into the evening on the East Coast as heat index values reach 100 to 105 in cities including Philadelphia, Washington, Baltimore and Raleigh, as well as Charleston, South Carolina, and Jacksonville, Florida.
Heat index values reflect what the temperature feels like to the human body.Temperatures will finally start to drop this week, with highs generally in the 70s to low 90s throughout the East Coast.Visitors grab bottles of cold water at the Great American State Fair on the National Mall in Washington, D.C., on Saturday.Anna Rose Layden / Getty ImagesIn the Southwest, extreme heat watches cover parts of Arizona and California, including Phoenix and Tucson, and go into effect Tuesday through Thursday.Dangerously hot conditions are expected through midweek, with daytime highs reaching as high as 114 degrees.At least 25 people have reportedly died in the ongoing heat wave, with most of the suspected deaths in New Jersey, where 22 people have died across 10 counties, according to the state’s Department of Health.Two deaths have been reported in Hinds County, Mississippi, and one in Cook County, Illinois, officials said.In New York City, more than 378 people have visited emergency rooms for heat-related illnesses, according to the city’s Health Department.Summer stormsSaturday’s storms produced more than 540 damagi...