Traveling to the Lofoten islands in early September. What should in terms of clothing and necessities for the climate? Is it cold enough to bring a winter coat?
Timeanddate.com has actual, historical, day-by-day weather statistics for just about anywhere you might want go, including the Lofotens. Take a look at Sep 2021, Sep 2020, Sep 2019, etc , to see wmight expect.
I haven't been as far north as the Lofotens, but I'd consider the impact of wind as well as temperature. I've felt some distinctly chilly blasts of wind this summer in Scandinavia even though the weather has generally been warm.
Keep in mind that Bergen gets an extraordinary amount of rain. It has an average of 17 rainy days in September, totaling over 10 inches of rain for the month.
Probably not cold enough for a winter coat, but it depends on where you live and what temperatures you are used to.
My suggestion would be a thin and light wind/water-proof jacket and add layers below if you are cold.