Not with rain and 15 mph winds
Nah, he'll still warm up quickly.
I ran the Baton Rouge Beach half when it was 30ish and spitting rain around the start.
I went with a $5 sweatshirt, over a tech shirt with long sleeve Under Armour and gloves (and shorts.) Ditch the sweatshirt when you warm up, and if your hands get too warm, tuck the gloves in your waistband.
You can probably skip the UA in those temps.
Can someone meet you at the halfway point with a dry shirt?