Import volumes at major US retail container ports are set to increase 12.4% year-on-year in March as retailers begin to stock up for spring and summer. 

But the forecast from the monthly Global Port Tracker report released by the National Retail Federation (NRF) and Hackett Associates is slightly lower than the 13.7% rise first predicted.

"Retailers are bouncing back from the annual post-holiday slowdown and getting ready for the surge in activity that comes each year as the weather warms up," said Jonathan Gold, NRF vice president for supply chain and customs policy.

He expects shelves to be "well-stocked" with everything from bathing suits to barbecues. 

"Congestion has been a problem for many ports during this slowdown, so operations will need to improve to handle the expected surge in the coming months," Gold said.

Cargo movement at some ports has recently been slowed by a number of issues, including severe winter weather as well as labour and equipment shortages. 

Cargo import numbers do not correlate directly with sales because they count only the number of cargo containers, not the value of the merchandise inside them. The amount of merchandise imported nonetheless provides a rough barometer of retailers' expectations.

US ports followed by Global Port Tracker handled 1.36m Twenty-Foot Equivalent Units (TEU) in January, the latest month for which after-the-fact numbers are available. That was up 5.3% from December and 4.1% from January last year. One TEU is one 20-foot cargo container or its equivalent.

February, historically the slowest month of the year, was estimated at 1.17m TEU, down 8.8% from the same month last year.

March is forecast at 1.28m TEU, up 12.4% from last year; April at 1.36m TEU, up 5.1%; May at 1.44m TEU, up 3.7%; June at 1.43m TEU, up 5.3%, and July at 1.49m TEU, up 3.4%. The first half of the year is expected to total 8m TEU, up 3.5% on last year. The total for 2013 was 16.2m TEU, up 2.3% from the prior year's 15.8m TEU. 

"At the end of the day, it all depends on consumption," noted Hackett Associates founder Ben Hackett.

"We cannot escape the basic tenant of economics that demand determines growth or weakness. Somehow, the average consumer needs to be given the economic confidence to go out and spend. Without that, the economy will remain weak and no amount of tinkering by the Federal Reserve will have much of an impact."