Import cargo volume at the nation’s major retail container ports should see its traditional buildup toward the summer, despite difficult comparisons with last year’s unusual patterns, according to one report.

According to the monthly Global Port Tracker report released by the National Retail Federation and the consulting firm Hackett Associates, ports covered in the survey handled 1.5 million 20-foot equivalent Units (TEUs) in January, the latest month for which after-the-fact numbers are available.

That was up 4.4% from December and 21.4% from unusually low figures in January 2015, the month before a new contract with dockworkers was signed to end a near-shutdown at West Coast ports.

“Comparisons are still complicated because of last year’s situation at the West Coast ports but should clear up in the second half of the year,” said NRF vice president for supply chain and customs policy Jonathan Gold. “Year-over-year numbers are skewed but on a monthly basis imports are building normally as the back-to-school season approaches.”

February was estimated at 1.4 million TEUs, up 17.1% from the same month in 2015 and also skewed by last year’s congestion. March is forecast at 1.35 million TEUs, 22.2% lower from the flood of traffic seen as the backlog of cargo began to move through ports at this time last year. April is forecast 1.8% less from last year; May 3.4% lower; June down 1.6%; and July 0.4% less.

The first half of 2016 is expected to be down 0.2% from the same period in 2015.

With cargo volume down so far this year, Hackett Associates Founder Ben Hackett said recent decisions by major shipping lines to add new super-large capacity vessels to routes between Asia and the U.S. West Coast are likely to bring lower shipping rates at the risk of “chaos” in the balance between supply and demand.

“Does this make sense? Absolutely not,” Hackett said. “It flies in the face of financial and economic wisdom and totally ignores the state of the freight market.”

Global Port Tracker covers the U.S. ports of Los Angeles/Long Beach, Oakland, Seattle and Tacoma on the West Coast; New York/New Jersey, Hampton Roads, Charleston, Savannah, Port Everglades and Miami on the East Coast, and Houston on the Gulf Coast.