The phrase "keep weather-eye out" is an old nautical term that means to be watchful or vigilant. There are several synonyms that can be used in place of this phrase to convey the same message. Some examples include "be on the lookout," "stay alert," "keep your eyes peeled," "remain observant," "stay attentive," and "stay vigilant." All of these phrases communicate the importance of being aware of one's surroundings and paying attention to any potential dangers or risks. Whether you're on a ship at sea or navigating through life on land, it's always a good idea to keep a weather-eye out and stay alert to your surroundings.