Climate Impact Company U.S. population weight CDD forecasts for meteorological summer 2024 issued during late May/early June were closest to the observed values. As time went on, subsequent forecasts were much warmer propelled by fear of drought-induced heat in the Central U.S. and anomalous warmth in high energy demand areas of the East U.S. fueled by very warm SSTA off the Atlantic Coast.

A steady and intense positive phase of the southern oscillation index (+SOI) has developed since mid-August causing trade winds across the eastern equatorial Pacific to increase and begin to up-well cool subsurface water to turn the Nino34, Nino3, and Nino12 SSTA cooler during the past 7-10 days.

The largest surprise in forecast models is the increase in rainfall in the 15-day outlook for Northeast Argentina, Uruguay, and Southeast Brazil. The AIFS forecasts consistent rains piling to several to 6 inches due to a quasi-stationary frontal boundary in the region.

Massive amounts of thunderstorm activity is percolating in the western Gulf of Mexico. A widening area of thunderstorms along a low-pressure trough emerges, lasts for many days, and produces 15-20 in. of rain near the Texas/Louisiana coast.