WASHINGTON — The National Retail Federation (NRF) said it expects retail sales, excluding automobiles, gasoline and restaurant meals, to increase 3.6% to $655.8 billion in November and December. That would mark an acceleration over the 3% growth in the final two months of 2015 and represent a significant increase from the 10-year average of 2.5% growth, NRF said.

NRF forecasts that non-store sales, which skew toward digital, will increase between 7% and 10% in November and December.

The trade group’s forecast is based on an economic model that factors in consumer credit, monthly retail sales and personal income.

“All of the fundamentals are in a good place, giving strength to consumers and leading us to believe that this will be a very positive holiday season,” said NRF president and chief executive officer Matthew Shay. “This year hasn’t been perfect, starting with a long summer and unseasonably warm fall, but our forecast reflects the very realistic steady momentum of the economy and industry expectations. We remain optimistic that the pace of economic activity will pick up in the near term.”

Holiday sales account for about 20% of retailers’ total for the year and can be as high as 40% for some retailers, NRF said. It also said about 40% of consumers begin their holiday shopping before Halloween each year.

“Consumers have seen steady job and income gains throughout the year, resulting in continued confidence and the greater use of credit,” said Jack Kleinhenz, NRF’s chief economist.