South of St Kilda, Atlantic water reaches the edge of the Continental Shelf west of the Hebrides from the eastern side of the Rockall Channel, whereas the main north-east going current from the western side of the channel probably lies close to the shelf-edge to the north of St Kilda. On the shelf, Atlantic water mixes with Clyde and Irish Sea water to the south-west of the Small Isles, and the mixed water so formed diverges to flow partly northward through the Little Minch and partly southward to Barra Head, then northward along the western coasts of the Outer Hebrides. On the outer shelf, dense winter-formed bottom water persists into the autumn, implying that advection is weak in this region in summer.
Data of temperature and salinity are sparse around the Outer Hebrides. Annual temperature cycles at depth on the shelf can be explained in terms of the cycle of wind mixing. A non-divergent Continental Shelf wave gives rise to strong diurnal components in the tidal streams upon the outer shelf and in the Sound of Harris, but causes no perceptible disturbance to the semi-diurnal rise and fall.