Import traffic at the nation's 11 major container ports is expected to have risen more than originally predicted during the holiday period, according to the monthly "Global Port Tracker" report released today by the National Retail Federation (NRF) and consultancy Hackett Associates.

The ports handled 1.64 million twenty-foot equivalent units (TEU) of containers in November, the latest month for which actual numbers are available, according to the data. That was down 1.6 percent from October, but up 11.2 percent from November 2015. Global Port Tracker had previously predicted a year-over-year increase of just 3.6 percent. Ocean container flows in November usually decline from October's figures because most holiday import merchandise has already arrived in the U.S. by Halloween.

December traffic, which is still being tallied, is estimated at 1.54 million TEU, up 7 percent year over year. The original forecast was for a 3.2-percent increase.

Cargo volume does not correlate directly to sales because only the number of containers is counted, not the value of the cargo inside. However, NRF and Hackett contend that it provides a useful barometer of retailers' expectations. NRF has predicted sales totaling $655.8 billion during November and December, a 3.6-percent increase over 2015. November sales rose 5 percent year over year. The Commerce Department is scheduled to release December numbers on Friday.

Cargo volume for 2016 is now estimated at 18.8 million TEU, up 2.9 percent from 2015. The original forecast was a 2-percent year-over-year gain.

"We won't see final sales numbers for a few more days, but import volume suggests that retailers had a strong holiday season," Jonathan Gold, NRF's vice president for supply chain and customs policy, said in a statement. "Retailers don't import merchandise unless they think they can sell it."

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