The ferry operator said on Sunday morning that its southbound service to Aberdeen would now leave Lerwick at 3pm, four hours ahead of the scheduled departure.
The northbound service from Aberdeen to Lerwick via Kirkwall will operate close to timetable though arrival in Shetland on Monday morning could be delayed.
Meanwhile Monday night’s ferry services are under review in the light of the worsening forecast (now named Storm Brendan) with a probability of cancellation, NorthLink said.
A decision on whether or not these sailings can go ahead will be made on Monday morning.
A full and detailed weather forecast, including wave and wind charts, can be found at our weather page at www.shetnews.co.uk/weather