GLOBAL Port Tracker notes a shift in Asian cargo from the US west to the east coast because of the congestion arising from bitter labour contract talks, but says it is unlikely to stick.

"Looking on the practical side, a number of factors favour a return to the west coast," said Ben Hackett, who does the number crunching for the National Retail Federation monthly port tracker report.

Mr Hackett said sending ships from Asia to the east coast is more expensive than the west coast, takes longer and results in greater expense to move the cargo to the Midwest.

In addition, he said, importers have significant investments in west coast distribution centres that would not easily be abandoned.

Nonetheless, west coast ports handled 55 per cent of cargo this January, down from 64 per cent during the same month in 2014, while east coast ports handled 45 per cent, up from 36 per cent, he said.

"Importers and exporters are reviewing their supply chain plans for the future, and not necessarily in favour of the west coast,?he said, suggesting some loss will be long-lasting.

Yet volumes through major US ports are expected to rise 16.9 per cent in March year on year as west coast dockers clear the backlog of cargo built up after bitter contract talks.

"The contract talks are over, but the tentative agreement still has to be ratified and it's going to take months to get back to normal on the west coast," said NRF vice president Jonathan Gold.

Ports covered by Global Port Tracker handled 1.24 million TEU in January, the latest month for which after-the-fact numbers are available.

That was down 13.4 per cent from December following the end of the holiday season and down 9.5 per cent from January 2014.

February was estimated at 1.27 million TEU, up 2.3 per cent from 2014. March is forecast at 1.52 million TEU as spring merchandise arrives, up 16.9 per cent from last year.

The March number is high both because of the backlog of ships at anchor waiting to be unloaded and because the annual Chinese New Year shutdown of factories was later this year, delaying some February cargo into March.

April is forecast at 1.51 million TEU, up 5.2 per cent; May at 1.57 million TEU, up 6.1 per cent; June also at 1.57 million TEU, up six per cent, and July at 1.6 million TEU, up 6.7 per cent.

The first half of 2015 is forecast at 8.7 million TEU, an increase of 4.5 per cent over the same period last year.

Port Tracker covers Los Angeles/Long Beach, Oakland, Seattle, Tacoma, New York/New Jersey, Hampton Roads, Charleston, Savannah, Port Everglades and Miami and Houston.