Information from The Met Office

An area of heavy rain will become slow-moving over the Northern Isles on Monday night and through Tuesday morning, before clearing from Orkney in the afternoon and eventually from Shetland during the evening.

Totals of 20-40 mm seem likely to fall quite widely, mostly within a 6 to 12 hour period, with perhaps as much as 50-80 mm in a few locations on Shetland. Strong winds accompanying the rain may also add to the difficult travelling conditions.