Emergency plans have been activated for millions of people across the U.S. East Coast as a combination of brutal heat and severe thunderstorms threatens to bring dangerous conditions, including flash flooding. The National Weather Service has issued heat advisories stretching across parts of New York, Connecticut, New Jersey, Pennsylvania, Delaware, Maryland, Massachusetts, and New Hampshire, as well as Washington D.C.
In New York City, Mayor Zohran Mamdani ordered a citywide response on Thursday as the city entered a heat advisory expected to last through Friday evening. The heat index in New York City could reach approximately 100°F, with even higher temperatures forecasted for Pennsylvania, New Jersey, and Delaware, potentially hitting 103°F. Southern Connecticut could experience heat index values exceeding 105°F.
Overnight temperatures are not expected to provide much relief, remaining in the low 70s before the oppressive heat returns Friday. The high temperatures are expected to coincide with thunderstorms capable of producing torrential rain, strong winds, and frequent lightning across the Northeast and Mid-Atlantic regions. Forecasters are warning of the potential for localized flash flooding, fallen trees, and downed power lines throughout Friday.
New York City officials have issued urgent warnings to residents in basement apartments, advising them to find safer shelter before floodwaters rise. Residents are urged to stay indoors during severe weather and avoid flooded roadways. The city is mobilizing resources, including cooling vans for older adults, and opening hundreds of cooling centers across the five boroughs. These centers will be accessible and pet-friendly, with locations available online or by calling 311.
The widespread heat advisories highlight the significant reach of the dangerous weather. In Connecticut, nearly the entire state is under an advisory, with heat index values potentially climbing above 105°F in some areas. Scattered thunderstorms are also anticipated on Thursday afternoon and evening, carrying the risk of heavy rain, lightning, and powerful wind gusts, which could lead to localized flooding in areas recently affected by downpours. Friday is expected to bring another round of intense heat and an increased likelihood of thunderstorms.
Similar conditions are affecting New Jersey, where heat index values may reach 103°F, with warnings in effect through Saturday evening for many communities. Northeastern counties in New Jersey also face thunderstorms on Friday that could bring heavy rain and flash flooding. Farther south, a heavily populated region encompassing Philadelphia and parts of Pennsylvania, New Jersey, and Delaware could see heat index values of 103°F, with the advisory in place until Saturday evening.
The extreme heat and humidity pose a significant health risk, making it difficult for the body to cool itself and increasing the danger of heat exhaustion and heat stroke. Symptoms of heat exhaustion include dizziness, weakness, nausea, headache, and heavy sweating, while heat stroke can cause confusion, loss of consciousness, and dangerously high body temperatures, requiring immediate medical attention. Older adults, young children, outdoor workers, and individuals with chronic health conditions are particularly vulnerable. Residents are advised to drink plenty of water, stay in air-conditioned spaces, postpone strenuous outdoor activities, and never leave children or pets in parked vehicles.