Import cargo volume at the US' major retail container ports is expected to rise 4.8% in June against the same month last year, and year-over-year increases are expected to continue into the holiday season shipping cycle, according to research released by the National Retail Federation and Hackett Associates.

US ports followed by the Global Port Tracker handled 1.23m twenty-foot equivalent units (TEU) in April, a 3.9% increase from March and a 1.5% rise on April 2011. One TEU is one 20-foot cargo container or its equivalent.

May was estimated at 1.29m TEU, up 0.5% from a year ago and June is forecast at 1.31m TEU, up 4.8% from the same time last year. The Global Port Tracker is forecasting 1.36m TEU in July, up 2.5%; a 7.3% rise in August to 1.42m TEU; a 9% rise in September to 1.45m TEU and a 19.9% rise in October to 1.53m TEU.

"Retail sales have seen 22 straight months of year-over-year sales increases, and these import projections suggest retailers should see growth into the two-year mark and beyond," said Jonathan Gold, NRF vice president for supply chain and customs policy.

"Cargo numbers don't correlate directly into sales numbers, but they are an indicator of how much retailers think they can sell."