The weather on Norfolk is moderate basically all year round - one of the pluses of being an island - but it can be chilly at night especially in winter. It can be very windy and does rain at least once a day - very heavy but only for a short time. A lightweight water/wind proof jacket is essential. The sort that folds up into its own pocket is ideal.
How do I know this - I went without one and a store owner in Burnt Pine is the richer for it. That jacket goes everywhere with me now.