Seasonal fog along the US Gulf Coast is delaying containership arrivals at Houston and prompting diversions to Mobile, leaving exporters with little time to prepare freight and causing missed cutoffs, reports London's S&P Global.

Houston, the busiest US port when all ship traffic is considered, typically faces fog in winter. In December, 21 containerships waited at anchor with average delays of four days, according to Sea-web. Some vessels saw five-day dwells during the holiday period. CMA CGM warned of congestion spilling into 2026.

Carriers have reversed Gulf Coast rotations, calling Mobile before Houston. Since December, at least nine ships switched to Mobile-first calls, with Maersk, MSC, CMA CGM, Evergreen, ONE, HMM and Yang Ming among those adjusting schedules. Four other ships not regularly deployed to the Gulf also adopted Mobile-to-Houston rotations.

Exporters say they often receive only one-day notice of changes, leaving insufficient time to prepare containers. A Houston chemicals manufacturer said early arrivals have disrupted about 800 export boxes since December, forcing cargo to be rolled to later voyages and tightening space to Southeast Asia.

A Jacksonville freight forwarder said one Mississippi wood products client shipping 20-30 containers weekly has had to store loaded boxes that missed vessels, complicating USDA certification requirements. He criticised carriers for not being proactive in communication.

Maersk said it aims to inform customers quickly about weather-related disruptions. Port Houston Authority said it supports legislation by Texas lawmakers to expand observation and improve forecasting of fog events affecting navigation.