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Aeolian sediment transport under offshore winds is usually discounted from sediment budget considerations of coastal dunes. Results presented here indicate however, that depending on wind orientation and foredune morphology, positive contributions to the sediment budget can arise from offshore winds. Lee-side airfl ow patterns, seaward of the foredune crest, under offshore winds were studied at three sites of varying foredune geometry along Magilligan Strand, Northern Ireland. Ultrasonic anemometers recorded 1 Hz wind velocity data at 1° intervals. Descriptive statistics and wind rose diagrams were used in the analysis of these data. Under perpendicularly offshore winds each site exhibited a different type of lee-side airfl ow pattern. A tall (11·4 m), sharp-crested foredune produced fl ow separation with a recirculation cell. A lower (6·6 m), more rounded, foredune crest exhibited lee-side fl ow that remained attached but was defl ected parallel to the crest, while fl ow over a low incipient foredune crest resulted in attached fl ow with no defl ection in the lee. The morphology of the lee slopes best explained these airfl ow adjustments. More obliquely offshore winds were also found to affect the secondary airfl ow patterns, with a smooth transition from fl ow separation to fl ow attachment as the incident angle decreased. At higher wind velocities this smooth transition was replaced with a more abrupt switch between the secondary airfl ow types. This threshold was located at similar approach angles to those recorded for desert dunes (90° +/− 20°). These fi ndings have signifi cant implications for the post-storm recovery and long-term evolution of beach-dune systems where the predominant winds are offshore, and offer an explanation for the presence of many beach-dune systems in lee-coast locations.