The island can only be left by ferry, boat or plane. When seas exceed about 2 m, crossings are cut. Decide in advance what would make you leave, and keep a go-bag ready.
Preparedness
Decide your trigger in advance (for example: water cut for more than 3 days, or level Act with the sea about to close). Keep a go-bag with documents, medicine, cash, a day of water and food, a headlamp and rain gear. See the Exit plan (leaving the island) for routes and departure windows.