The U.S. Postal Service is preparing for a bump in the number of packages it handles over the winter peak shopping season, but predicts that surge will be slightly lower than recent years' totals.

USPS says its busiest season begins to ramp up beginning Dec. 9, then hits its maximum peak two weeks before Christmas, thanks to a spike in last-minute shopping. That annual surge will send a burst of more than 28 million packages per day through the carrier's network between Dec. 16 and Dec. 21, and then settle down to about 20.5 million packages per day through the remainder of the year, the agency said today.

In all, USPS plans to deliver a projected 800 million packages between Thanksgiving and New Year's Day. That number is down from the service's estimate of more than 900 million packages delivered between Thanksgiving and New Year's Day in 2018 and its forecast of 850 million packages it handled over that period in 2017.

The lower numbers run counter to market trends indicating that U.S. consumers will actually increase their holiday shopping in 2019, according to a National Retail Federation (NRF) forecast that holiday retail sales for the U.S. peak season during November and December will increase between 3.8 percent and 4.2 percent over their 2018 levels.

Despite that overall economic growth, USPS expects to handle fewer packages in the 2019 peak period than it did in 2018 in part because of a calendar fluke—there are six fewer days between Thanksgiving and Christmas this year, a USPS spokesperson said in an email.

Another reason for the dip is the "intense competition" USPS faces in the parcel delivery sector, the spokesperson said. Still, the agency said its central role as the nation's mail carrier will help it retain its crown. When the dust has settled after the 2019 peak season, USPS will have delivered more packages to homes than any other rival, the postal service said.

Revelers will also generate an estimated 2.5 billion pieces of first-class mail, including greeting cards, that must be processed and delivered in the week of Dec. 16. That statistic is also down from the nearly 3 billion pieces of first-class mail, including greeting cards, that USPS estimated it processed and delivered in the same week of 2017.

In order to handle the increased load, USPS says it will expand Sunday delivery beginning Nov. 24 to locations with high package volumes. USPS already delivers packages on Sundays in most major cities, and anticipates delivering more than 8 million packages on Sundays in December. Mail carriers will also deliver packages for an additional fee on Christmas Day in select locations, the agency said.

Editor's note: This article was revised on Nov. 7 to include comments from the U.S. Postal Service.

The Holidays are Coming! Do You Know the Shipping Deadlines?????????????

— U.S. Postal Service (@USPS) October 12, 2019