14 Dec of 1287 marked a terrible storm flood in the Netherlands that was named after the St. Lucy holiday that occurs about this time (see Badger's post under Sweden) -- the flood basically created the zuiderzee and thousands of people perished, but it also had profound effects on the coastline of England
https://www.villagenet.co.uk/history/1287-storms.php
Dunwich had been a major port in Suffolk, but it and other towns were altered by storms that winter, and their river access was ruined by silt.