El Nino remains firmly in place with sea-surface temperatures warmer than normal throughout much of the Equatorial Pacific Ocean. The latest long-range climate models now indicate that there is a 90% chance that this El Nino will persist through the upcoming winter and a 80% chance that it will last into next spring.
With that being said, this El Nino will likely have a major impact on temperatures for the winter season across much of the United States. As for the September temperature outlook, there are many climate indices that suggest that slightly above normal temperatures will occur across the northern Rockies and Pacific Northwest. Total monthly cooling degree days are projected to be higher than average by between 30 and 60. Parts of the Southeast may also see temperatures average a bit warmer than normal in September with total monthly cooling degree days at a surplus of 20 to 40. Both of these regions of the country will likely see at least slightly higher energy costs with respect to cooling.
On the flip side, slightly below normal temperatures are predicted across parts of the central and southern Plains and southern Rockies. These areas will see cooling degree day deficits of between 30 and 60 during the month of September. Much of the Midwest, Great Lakes, Northeast, and Mid-Atlantic is expected to see temperatures that on a whole average closer to normal for the month of September.