Import cargo volumes at major US retail container ports are expected to grow 1.8% year-on-year in December, as retailers remain well-stocked during the holiday season.

The forecast from the monthly Global Port Tracker report released by the National Retail Federation (NRF) and Hackett Associates comes as the NRF expects holiday sales to grow 3.9% year-on-year.

"Imports have seen good growth over last year and retailers are well-stocked as the holiday season continues," said vice president for supply chain and customs policy Jonathan Gold. "Holiday merchandise has made it from the ships to the shelves and the rest is up to the shoppers."

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. But the amount of merchandise imported nonetheless provides a rough barometer of retailers' expectations.

US ports followed by Global Port Tracker handled 1.43m Twenty-Foot Equivalent Units (TEU) in October, the latest month for which after-the-fact numbers are available. That was down 0.4% from September as the peak shipping cycle wound down, but was up 6.4% from October 2012. One TEU is one 20-foot cargo container or its equivalent.

November was estimated at 1.33m TEU, up 3.6% from last year. December is forecast at 1.31m TEU, up 1.8% from a year ago. January 2014 is forecast at 1.35m TEU, up 3.3% from January this year; February at 1.18m TEU, down 7.8% from last year; March at 1.32m TEU, up 15.9%; and April at 1.38m TEU, up 6.6%.

The first six months of 2013 reached 7.8m TEU, up 1.2% from the first half of 2012. The total for 2013 is forecast at 16.2m TEU, up 2.3% from last year's 15.8m TEU.

"The US economy appears to have found a growth spurt," Hackett Associates Founder Ben Hackett said, citing estimated third-quarter gross domestic product growth of 3.6%.

"The paradox is that consumer spending remains very cautious and does not come anywhere near the expansion of GDP. The reason is the increasing levels of inventory.

"Despite back-to-school sales, Black Friday, Cyber Monday and regular sales, the inventory-to-sales ratio remains stubbornly high. Hopefully, November and December numbers will show a catch-up that will help reduce the inventories."