A series of low pressure systems will dive into the Northeast and Mid-Atlantic from southern Canada over the next two weeks, which will bring cloud cover and rainy weather to the Northeast. Temperatures could warm up to normal levels between systems, but the majority of the time the Northeast will be hit by below normal temperatures, creating an abrupt change from extreme summer heat to cool fall weather. This pattern does not appear to be long-sustained, though, as ridging over the central U.S. could move warmer temperatures into the East going into the last week of September.
Meanwhile, the southern U.S. will get a period of above normal temperatures as the subtropical ridge sits over the region. Summer has been rather relentless down there this year as far as above normal temperatures, and it looks like it will be awhile before they will catch a break.
EDIT: I’ll probably be using a different U.S. map in the future… I was just trying this one out. The blue on the ocean may be a bit too distracting to the rest of the image.