keep a weather eye on (someone or something)

To monitor someone or something closely, often because the person or thing in question may turn out to be dangerous. Primarily heard in UK, Australia. I need you to keep a weather eye on this crisis so that we can get the necessary supplies out quickly.

If you keep a weather eye on something or someone, you watch them carefully so that you are ready to take action if there are problems. Keep a weather eye on your symptoms and stay alert to any changes which occur. Amy moved away from a neighbourhood where she'd kept a weather eye on an old lady. Note: Other prepositions are sometimes used instead of on, for example out and for. The police were there, keeping a weather eye out for trouble of any sort. Note: This expression was originally used by sailors, who had to keep a constant watch on the weather and wind direction.

To remain on guard, to watch out for trouble. In maritime language keeping a weather eye means looking toward the wind to observe weather conditions and look for squalls. The term appeared in a Sailor’s Word-Book (Smyth, 1867) but by the end of the nineteenth century was being used figuratively for keeping any kind of careful watch. Thus Lee Thayer used it (Murder Is Out, 1942), “You know how to keep your weather eye lifting.”