average water temperature in december in st. john
Climate & Weather â When to visit St. John. It is warm year-round on St. John. The average max temp. is 84-89Â°F, with August being the hottest month and Dec-Jan the coldest. The average min temp is 73Â°F-80Â°F. You will rarely need anything long, except for supermarkets, where it is freezing or to protect yourself from sunburn or bug bites. The average water temperature is 82Â°F.