Nearly 200 million Americans under heat wave advisories. Here's where it's the hottest.

A dangerous heat wave is affecting nearly 200 million Americans this week as some regions deal with record-breaking heat across the country. There are 35 states under heat advisories and some health officials are warning residents to stay inside to stay safe from the scorching hot temperatures. 

Residents in the Pacific Northwest will likely face triple-digit temperatures this week following a deadly heat wave that was blamed for 63 deaths in June, according to the National Weather Service. In Washington state, there were more than 1,300 hospitalizations caused by the heat at the time, officials said. 

"Yes, it's summer, but this type of heat can kill. Avoid strenuous activity during the midday, and bring along extra hydration, even if just going about normal business," the weather service tweeted Wednesday.

The Northeast is expected to set records for high temperatures in cities like Washington, D.C., Pittsburgh and New York City. Forecasters say added humidity could make the red-hot temperatures even more dangerous. Here's an overview of the cities facing the devastating heat across the country.

Oregon

The city of Portland is under an excessive heat warning until Saturday with "dangerously hot temperatures" between 95 and 105 degrees expected, according to the weather service. This is the state's second heat wave in three months, following June's high temperatures that left 45 people dead in Multnomah County. 

This week, Governor Kate Brown declared a state of emergency and directed state agencies to coordinate in order to protect critical infrastructure and prevent price gouging on life-saving resources like bottled water. 

"Oregon is facing yet another extreme heat wave, and it is critical that every level of government has the resources they need to help keep Oregonians safe and healthy," Brown said in a statement.

Winds have also brought large amounts of smoke from fires currently burning in British Columbia, the weather service said. Forecasters believe northwest Oregon will experience poor air quality, which will move to the Columbia River Gorge and Portland metro area late Thursday, marking one of Portland's haziest nights of the summer.

Northwest Oregon is expected to face 100-degree heat, and officials there cautioned residents to seek out local cooling centers. They also urged residents not to leave children or pets unattended in their vehicles. 

Washington state

In Seattle, heat warnings will remain in effect until Saturday night, with temperatures remaining around 90 degrees near the metro area. The city is on track to break several daily high records. Forecasters said the hottest temperatures will occur over the Southwest Interior, Cascade foothills and Cascade Valleys, with highs near 105 degrees. 

The extreme temperatures have also increased dry conditions in large parts of Washington. To prevent fire danger, residents are encouraged to refrain from outdoor burning near dry brush, parking in grass, mowing the lawn at the height of the day and disposing of charcoal before it's completely cool. 

There will be little relief overnight through Sunday. Temperatures will remain as high as 70 degrees overnight across the Eastern Puget Sound, Cascades and Seattle metro area, the weather service said. 

New York 

The New York metropolitan area is expected to see high heat and humidity beginning Thursday and continuing into the weekend, the weather service said. A "hot and humid air mass" will cause temperatures to rise to 110 in warning areas, with temperatures staying in the 70s at night. It could be the hottest day since 2016 for the NY metro area.

An excessive heat warning is in effect for the entire tri-state area, with only Suffolk and New London counties under a normal heat advisory. Residents are urged to be careful, as the high temperatures combined with the oppressive humidity can make the heat even more dangerous for at-risk groups or those who stay outside for "prolonged activity." 

Power company Con Edison has warned New York residents that the extreme heat wave could cause power outages and blackouts in some areas. Over 2,300 have already had service restored since the beginning of the week. Con Ed customers have been encouraged to limit the use of large air conditioners to prevent larger blackouts in the city. 

For those exposed to the heat, city officials have also opened cooling stations throughout all five boroughs for those unable to access air conditioning or "experiencing physical discomfort" due to the heat. A full list of centers can be found here.

Pennsylvania

The city of Pittsburgh is expected to see temperatures reach 91, with real-feel temperatures of about 100 to 105 degrees on Thursday. The city is on its fourth day of extreme heat, and in the middle of its fourth driest stretch in history. 

Thursday has the potential to be "the hottest day of the year region-wide," according to CBS Pittsburgh. Heat advisories are still in place for the towns of Indiana, Cambridge, Butler, New Castle and Washington.

Later this week, forecasters are hoping severe thunderstorms will do their best at cooling down temperatures but warned they could bring damaging winds with them.

Washington, D.C

The Baltimore-Washington, D.C., metro area is on a high-temperature alert, with officials warning that cities could see record-breaking temperatures the next three days. 

Forecasters said the nation's capital will see a high of 106 degrees on Thursday, while Baltimore could reach 109. These dangerous temperatures will extend into surrounding counties, with portions of Maryland, Virginia and eastern West Virginia experiencing heat index values between 105 and 110.

Heat waves can cause extremely dangerous conditions for the elderly, young and those who are outside for too long, the weather service said Thursday.  

"Extreme heat and humidity will significantly increase the potential for heat-related illnesses, particularly for those working or participating in outdoor activities," it added.

Residents are encouraged to prepare for the high heat by drinking plenty of fluids, staying out of the sun, reducing work outside and watching for signs of heat exhaustion.

David Parkinson contributed reporting.