Stony Brook University canceled all classes before 11 a.m. Tuesday and delayed opening its offices after an early morning thunderstorm caused a power outage and left downed trees and wires on the main campus.

University Police advised that students and staff exercise caution while navigating the campus as maintenance crews cleared hazards. The north entrance was closed around 2:15 p.m.

By 10:30 a.m. Tuesday, power had been restored to Stony Brook’s west and east campuses but not to the Research and Development Park. PSEG Long Island reported that almost 30,000 customers were still experiencing outages by 1:30 p.m.

Stony Brook’s delayed openings did not affect University Hospital and Long Island State Veterans Home, and the storm did not affect the Southampton and Manhattan campuses.

Suffolk County Police advised motorists to avoid Route 25A in Stony Brook, Port Jefferson and Setauket due to downed wires and trees, and the Long Island Rail Road suspended service on the Port Jefferson branch at about 6 a.m. due to a downed tree and power lines west of Stony Brook. Commuters traveling between Smithtown and Port Jefferson had to be accommodated by bus as crews cleared the tracks.