NorthLink has issued a warning over weather-related delays.
The ferry operator says the current forecast indicates the possibility of disruption to services from Thursday through to Friday.
Updates will follow as forecasts are updated.
It has already decided tomorrow’s south-bound sailing of the freight vessel Hildasay will begin at 4pm, instead of the scheduled departure time from Lerwick of 6pm.
Her voyage back from Aberdeen on Thursday is under review, with the possibility of cancellation.
Thursday’s south-bound freight service could also be cancelled.