The National Oceanic and Atmospheric Administration has forecast that temperatures for the months of August, September and October will be above average for the United States, including both the contiguous states and Alaska. According to research into NOAA’s archives on the matter done by Gizmodo, a forecast stretch of above-average temperatures this long is unprecedented.
While the 2015-2016 El Niño cycle has officially ended, the Pacific Ocean is still venting leftover heat from that record-breaking event, contributing to warmer temperatures. This is in addition to the overall global average temperatures, of which continue to break monthly records.
One thing to bear in mind is that this forecast is for the average temperatures for these three months — this does not necessarily mean that the entire country will suffer a three-month heat wave, or that these temperatures will actually last for the full three months, but that some areas are expected to be well above average, while some might see lower than average temperatures.