Import volumes at major US retail container ports are forecast to grow 3.5% in May, as negotiators prepare to begin talks on a new contract for West Coast dockworkers.

The forecast from the monthly Global Port Tracker report released by the National Retail Federation (NRF) and Hackett Associates comes as the retail trade association predicts 4.1% sales growth in 2014. While cargo volume does not correlate directly with sales, it is a barometer of retailers' expectations.

Representatives of the Pacific Maritime Association and the International Longshore and Warehouse Union are scheduled to start talks next week on a new contract to replace the current agreement, which expires on 30 June. 

NRF has urged both sides to avoid any disruptions that could affect the flow of back-to-school or holiday season merchandise.

West Coast ports handle more than two-thirds of US retail container cargo each year, including the bulk of cargo from Asia. The lastest major shutdown there in autumn 2002 closed ports for ten days, and created a week-long backlog. 

"We're expecting a lot of cargo to move through the ports this summer and we want to make sure there aren't any supply chain disruptions that would impact the cargo flow," said NRF vice president for supply chain and customs policy, Jonathan Gold.

"We hope there won't be any issues, but the sooner labour and management can agree on a new contract, the better it will be for everyone who relies on the West Coast ports."

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 1.3m Twenty-Foot Equivalent Units (TEU) in March, the latest month for which after-the-fact numbers are available.

The number was up 5.1% from February, traditionally the slowest month of the year, and up 14.5% from March 2013. One TEU is one 20-foot cargo container or its equivalent.

April was estimated at 1.38m TEU, up 6.1% from the same month last year. May is forecast at 1.44m TEU, up 3.5% from last year; June at 1.43m TEU, up 5.6%; July at 1.49m TEU, up 3%; August at 1.5m TEU, up 0.8%, and September at 1.44m TEU, up 0.1%. The first half of the year is expected to total 8.2m TEU, up 5.1% over last year.

The total for 2013 was 16.2m TEU, up 2.3% from 2012's 15.8m TEU.

"Most economic fundamentals are pointing in the direction of continued, sustained recovery in consumer demand and import volumes," said Hackett Associates founder Ben Hackett. 

"This is turning out to be the longest period of growth for some time now."