A heatwave and stifling humidity battered the central and eastern United States, leaving residents searching for the coolest oasis to fend off record temperatures that have left over 20 dead. \"The dangerous heatwave continues across much of the central and eastern United States, with excessive heat and humidity expected to expand into the Ohio Valley and East Coast states for the remainder of the week,\" the National Weather Service (NWS) said on its website. The New York Times reported that across the country the deaths of 22 people had been attributed to the heatwave, which has left some 17 states from Texas to Michigan battling temperatures over 100 degrees Fahrenheit (37 Celsius). The weather service has issued excessive heat warnings for those states saying there is a \"large ridge of high pressure in the upper levels of the atmosphere... keeping hot temperatures in place.\" Weather experts predicted that heat index values across parts of the Midwest, Ohio Valley and Mid-Atlantic could reach between 105 and 115 degrees Fahrenheit (40 to 46 Celsius) through Friday. A heat index of 123 degrees Fahrenheit (51 Celsius) was registered in Iowa, in the central United States. In Maryland, near the US capital, weather services reported temperatures of 108 degrees Fahrenheit (42 Celsius). On the East Coast, humidity was assaulting Washington, where some residents walked under sun umbrellas. Others took advantage of evening outdoor movie screenings to cool down during night-time hours. The intense heat is set to stay in place through the weekend, sending Americans flocking to outdoor pools and air-conditioned shopping malls. In Oklahoma City, forecasters said the city has had 27 days this year of triple digit temperatures. Things were so bad in the town of Enid, Oklahoma, that the asphalt at a busy intersection crumbled in the heat. Cities like Chicago and Detroit have opened cooling centers. And in Omaha, Nebraska, one amusement park owner had to put two tonnes of ice cubes into his swimming pools to lower the water\'s temperature to 82 degrees. Further over toward the West Coast, where temperatures often soar in the summer months, there were few hot weather warnings signalled by the NWS. Small parts of Utah had a red flag warning in place -- indicating a heightened fire risk -- but temperatures were well within normal ranges in Arizona, California and up the coast in Oregon and Washington. In Death Valley, California, famous as the hottest and driest place in North America, the average maximum temperature forecast this week was around 115 degrees, although it will cool from Sunday to around 106, according to the NWS. But on the east coast the swelter continued. Late Wednesday, hundreds of people gathered on a lawn in Northeast Washington to watch the aptly titled Marilyn Monroe film: \"Some Like it Hot\" at a free film screening.