The University of Washington's Institute for Health Metrics and Evaluation's model forecasts that daily deaths from the coronavirus could surge from 765 to 3,000 by late December.
The United States leads the world in cases and deaths, reporting 7,093,285 cases and 204,606 deaths, according to data gathered by John's Hopkins University.
IHME Director Dr. Chris Murray said the model shows a "huge surge" beginning in October and accelerating through the end of the year, warning that the winter surge may have already begun in Europe.
"Cases are exploding there. So we know it's coming and we expect it to hit the U.S. pretty soon," he said.
Murray added that changes in behavior due to easing of coronavirus restrictions and an increase in indoor activities due to cooler weather are likely to contribute to the surge.
"First, as case counts have come down in some states, we tend to see that people become less careful, they tend to have more contact," Murray said. "But then the most important effect is the seasonality of the virus, that people go indoors, transmission happens more."
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, warned U.S. cities and counties to brace for "the challenge" of fall and winter as the nation averages more than 40,000 cases nationwide.
"You don't want to enter into the fall and winter with a community spread at that level, because if you do, you got a difficult situation that's going to be really challenging," he said.
Johns Hopkins data shows that at least 24 states are reporting an increase in new cases compared to the previous week.
California, which leads the nation in COVID-19 cases with 802,308, reporting 4,071 new cases on Sunday and added 55 new deaths for the third-highest death toll at 15,587.
Second-place Texas reported 1,292 cases for a total of 735,132 cases and 37 new deaths for the fourth-highest death toll at 15,522.
Florida reported 1,882 new cases on Sunday bringing its total to 700,564 -- third place in the nation -- and 10 new deaths for the fifth-highest death toll in the country at 13,032 as Gov. Ron DeSantis signed an executive order Friday transitioning the state into Phase 3 of reopening allowing restaurants and bars to operate at 100% capacity.
Miami Mayor Francis Suarez on Sunday criticized DeSantis' decision, saying reopening bars and removing fines for people not following restrictions presents a "significant handicap" to virus containment efforts.
"This is a very dangerous time," Suarez said on CNN. "This is definitely an acceleration. It's a lot faster than we had planned."
New York reported 866 new cases placing it fourth in the nation with 455,626 cases and six new deaths for the nation's highest total at 33,131, including probable deaths. On Saturday, it reported more than 1,000 cases for the first time since early June.
New Jersey, which ranks second in the nation in deaths at 16,103 after three new deaths on Sunday, also recorded its highest daily case numbers since June 4 at 712 for a total of 202,850, ninth in the nation.
Fifth place Georgia reported 826 new cases Sunday for a total of 314,685 and 32 new deaths for the 10th highest death toll at 6,946.