The Port of Long Beach is  a major shipping hub for U.S.-Asia cargo.

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 the monthly Global Port Tracker report released Tuesday by the National Retail Federation and Hackett Associates.

“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 Jonathan Gold, NRF vice president for supply chain and customs policy. “Year-over-year numbers are skewed, but on a monthly basis imports are building normally as the back-to-school season approaches.”

Ports covered by Global Port Tracker handled 1.5 million Twenty-Foot Equivalent Units in January, the latest month for which data is available. That was up 4.4 percent from December and 21.4 percent 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. One TEU is one 20-foot-long cargo container or its equivalent.

February was estimated at 1.4 million TEU, up 17.1 percent from the same month in 2015 and also skewed by last year’s congestion. March is forecast at 1.35 million TEU, down 22.2 percent from the flood of traffic seen as the backlog of cargo began to move through ports at this time last year. April is forecast at 1.49 million TEU, down 1.8 percent from last year; May at 1.56 million TEU, down 3.4 percent; June at 1.54 million TEU, down 1.6 percent, and July at 1.61 million TEU, down 0.4 percent.

The first half of 2016 is expected to total 8.8 million TEU, a 0.2 percent decline from the same period in 2015. Total volume for 2015 was 18.2 million TEU, a 5.4 percent gain from 2014.

With cargo volume down so far this year, Ben Hackett, founder of consulting firm Hackett Associates, said recent decisions by major shipping lines to add new superlarge 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.

Hackett said this move “flies in the face of financial and economic wisdom and totally ignores the state of the freight market.”

The CMA CGM Group, one of the world’s largest ocean freight shippers, said last week that it will deploy its flagship fleet of six 18,000 TEU vessels between Asia and the U.S. West Coast starting at the end of May as part of its growth strategy.

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

The Port of New York and New Jersey, the nation’s third-busiest facility, said last month it had exceeded its previous record for annual cargo volumes in 2015 by 10.4 percent, handling 6.37 million TEUs.