"Ports and distribution centers are getting the break they deserve after the busy holiday season, but it won't last long," Vice President for Supply Chain and Customs Policy Jonathan Gold said. "Retailers will be moving spring merchandise toward their shelves in just a few weeks, and early numbers point to a busy season ahead."

U.S. ports followed by Global Port Tracker handled 1.3 million Twenty-Foot Equivalent Units in December, the latest month for which after-the-fact numbers are available. That was down 3.3 percent from November as the holiday season came to an end but up 0.6 percent from December 2012. The December numbers brought 2013 to a total of 16.2 million TEU, up 2.3 percent from 2012's 15.8 million TEU. One TEU is one 20-foot cargo container or its equivalent.

January was estimated at 1.37 million TEU, up 4.5 percent from January 2013. February, historically the slowest month of the year, is forecast at 1.17 million TEU, down 8.4 percent from the same month last year. March is forecast at 1.29 million TEU, up 13.7 percent from last year; April at 1.39 million TEU, up 6.9 percent; May at 1.45 million TEU, up 4.2 percent; and June at 1.43 million TEU, up 5.6 percent. Those numbers would total 8.1 million TEU for the first half of the year, up 4.3 percent over last year.

The import numbers come as NRF is forecasting 4.1 percent sales growth in 2014, contingent on how Washington policies on economic issues affect consumer confidence.

"On the consumer side, there is continued hesitancy in spending as net disposable income remains virtually flat," Hackett Associates Founder Ben Hackett said. "As a result, the inventory-to-sales ratio remains stubbornly high."

Global Port Tracker, which is produced for NRF by the consulting firm 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.

Source: National Retail Federation