In what could be a sign of happy holidays for retailers this year, import volume at the nation’s major retail container ports is expected to grow 5.1% in September over the same month last year, according to the monthly Global Port Tracker report from the National Retail Federation and Hackett Associates.

“Retailers are making up for the slow imports seen earlier in the year,” says Jonathan Gold, NRF’s vice president for supply chain and Customs Policy. “It’s too early to predict holiday sales, but merchants are clearly stocking up.”

Cargo import numbers do not correlate directly with retail sales or employment because they count only the number of cargo containers brought into the country, not the value of the merchandise inside them. But the amount of merchandise imported nonetheless provides a rough barometer of retailers’ expectations.

U.S. ports followed by Global Port Tracker handled 1.43 million twenty-foot equivalent units (TEUs) in July, the latest month for which after-the-fact numbers are available. That was a 5.4% increase over June and up 1.1% from July 2012, and follows year-over-year declines in three of the four previous months. One TEU is one 20-foot cargo container or its equivalent.

August was estimated at 1.48 million TEUs, up 4.1% from last year. September is forecast at 1.48 million TEUs, up 5.1%; October at 1.46 million TEUs, up 9%; November at 1.31 million TEUs, up 2.2%; and December at 1.3 million TEUs, up 0.7%. January 2014 is forecast at 1.33 million TEUs, up 1.9% from January 2013.

The total for 2013 is forecast at 16.2 million TEUs, up 2.5% from 2012’s 15.8 million TEUs. The first six months of 2013 totaled 7.8 million TEUs, up 1.2% from the first half of 2012.

“The U.S. economy is on the road to sustained growth,” predicts Ben Hackett, founder of consulting firm Hackett Associates. “Second-quarter GDP was well above expectations and surprised most forecasters, the unemployment picture is improving, and we believe consumer confidence will translate into increased sales during the fourth quarter.”

Global Port Tracker, which is produced for NRF by Hackett Associates, covers the U.S. ports of Los Angeles/Long Beach, Oakland, Seattle and Tacoma on the West Coast; New York/New Jersey, Hampton Roads, Charleston, Savannah, Port Everglades and Miami on the East Coast, and Houston on the Gulf Coast.