“Travel will be very difficult to impossible, including during the evening commute on Wednesday,” the service wrote.

The Metropolitan Transportation Authority said it would send information on its storm preparations later on Tuesday, but did not anticipate Tuesday evening’s commute to be affected.

Alternate-side parking will be suspended Wednesday and Thursday in the city. Mr. de Blasio said he instructed the city’s sanitation department to move to 12-hour shifts for the storm. A “code blue” is also in effect for the homeless in New York City, greatly expanding their shelter options.

New Jersey Transit announced that it would run a limited weekday rail schedule on Wednesday, and that it would be cross-honoring tickets across rail, bus, light rail and PATH services. Buses and light rail lines in New Jersey were expected to operate on regular schedules as long as conditions permit, though officials also indicated it was possible that all bus routes would be suspended for Wednesday evening’s commute.

The National Weather Service said “minor to moderate coastal flooding” was likely for vulnerable areas of Long Island and New Jersey, and it predicted rough surf along the shore.