The island of Sanctuary is a flat disc about 200 miles in diameter. Sanctuary lies within a pocket dimension, so it has an artificial sun. The artificial sun is roughly 100 miles above the island; it turns itself on and off in a day/night cycle, and it circles above the island at a radius of about 50 miles. The ocean is connected to the Elemental Plane of Water (and the atmosphere is connected to the Elemental Plane of Air), which has a constant cooling effect on the island; the sun produces enough heat to keep the island comfortable.
What sort of weather does this lead to?
My guess is: rain happens at night, when the sun is off and the air cools. Rain does not happen during the day, because the air is warming up.
But what happens with the winds? Are there strong winds blowing away from the sun during the day and towards it at night? Is the wind and rain stronger on the edge of the island that's far from the sun, or is it stronger near the sun?