A blizzard watch was upgraded to a warning Tuesday afternoon as a powerful ocean storm stayed on track to lash the Vineyard overnight with heavy snow, flooding at the time of high tides and gale-force winds.

The National Weather Service in Taunton said snow would begin after 10 p.m. Tuesday and continue through midday Wednesday.

In advance of the oncoming storm ferry cancellations were expected, town hall closings were announced and the Vineyard Transit Authority said service interruptions were expected. All Cape Air flights were cancelled. A decision about public schools will be made at 5 a.m. Wednesday, Vineyard schools superintendent James H. Weiss told the Gazette.

The heaviest snow will fall between 2 a.m. and noon on Wednesday, the weather service said. “Travel may become impossible at times,” an announcement said.

Steady gale-force winds gusting to hurricane force are expected. Total snow accumulation between five and 10 inches is predicted.

Island emergency managers were preparing for the storm Tuesday afternoon, although the sun was shining on a cold March day.

All Oak Bluffs municipal buildings, including town offices, the library and council on aging will be closed on Wednesday. Town fire chief John Rose said East Chop Drive from Munroe to Brewster avenues will be closed from 6 a.m. Wednesday until 8 a.m. Thursday. Flooding is expected at the time of high tide Wednesday morning and could force the closure of Beach Road, Chief Rose said. High tide is at 8:30 a.m. in Nantucket Sound off Beach Road.

The West Tisbury town hall will be closed until noon on Wednesday.

A parking ban goes into effect in Tisbury beginning at 10 p.m. Tuesday. Tisbury town offices and the public library plan to open at noon on Wednesday.

The YMCA of Martha’s Vineyard will be closed until noon on Wednesday.

The Coast Guard first district issued an advisory for mariners Tuesday afternoon urging all boaters to seek safe shelter in advance of the storm, which is packing hurricane-force winds that will be felt hundreds of miles away.

The Vineyard, Nantucket, outer Cape Cod and Rhode Island are expected to feel the worst effects of what forecasters are calling a dangerous storm.