I'd go wearing the dress, but with a smart mac or trenchcoat and a pashmina.
Sleeveless might be a bit too chilly and the pashmina could cover upper arms and shoulders without detracting.
A blazer, cardigan etc will detract from the dress, and won't go with it.
If you haven't got a mac or trench, as long as you take it off immediately, I'd take a lightweight hooded waterproof.
The duster coat and cape on the previous page look cheap. You don't have to spend loads to get something that doesn't look cheap.