WASHINGTON, July 19 (Xinhua) -- As a major heat wave descends on the eastern United States, U.S. weather agencies have warned of hazardous conditions in multiple cities.

The National Weather Service (NWS) said the dangerous heat wave "will persist through this weekend" as it issued widespread warnings and advisories for the heat covering most of the eastern part of the United States.

The NWS warned Friday heat indices will surge past 38 degrees Celsius and even rise above 43 degrees Celsius in many locations.

"Northwest of this dome of heat, severe thunderstorms with the possibility of strong tornadoes and widespread significant wind damage are possible" into Friday evening, the NWS said in an alert.

The heat wave is predicted to peak Saturday, when the temperature is likely to break historical records in many cities.

Cities including Washington D.C., Baltimore, New York City and Boston are all expected to experience temperatures north of 38 degrees Celsius over the weekend, with the possibility of topping 43 degrees Celsius during late morning or afternoon.

Humidity of around 50 percent will exacerbate the heat spell for the east coast region this weekend. According to the NWS, a temperature of 43 degrees Celsius will feel like 66 degrees Celsius under 50 percent humidity.

Cities in the heat wave's path have scrambled to crank up the preparing effort. Washington D.C. activated a heat emergency plan Tuesday, and by Wednesday, Philadelphia and New York City had declared emergencies as well. Officials in Washington D.C., Philadelphia, New York City and Boston are cautioning local residents to stay out of heat and look out for friends and neighbors.

Energy providers are also bracing for the surge in energy consumption, and advising customers to refrain from keeping room temperatures too low.

"We ask that our customers set their thermostat at 78 degrees (25.5 degrees Celsius)," energy provider Pepco's media relations manager Christina Harper told weather tracker AccuWeather. "I know that sounds hot, but it's 22 degrees cooler than what's expected in the forecast."

The excessive heat is also expected to cause damage to the Midwest farming communities as well, as corn and soybeans are undergoing a critical time that needs sufficient rainfall.

"We're in a critical time period where if you're not getting rain, things go downhill," said AccuWeather Senior Meteorologist Jason Nicholls.

Any losses as a result of the heat will add to the woes of U.S. farmers, who are already struggling to recover from a wet spring.

The heat spell in the United States are part of a global pattern of high temperatures, after Europe and India have all endured blistering heat in previous weeks.