Like with most things that survive in menswear, the storm tab serves a very useful purpose and has its roots in the field.
It’s a simple thing, a removable suede, leather or heavy piece of fabric that buttons behind the collar, and, when deployed, crosses the throat and buttons to the other side of the under collar, effectively sealing out wind and cold, dog bites (depending on the thickness of the sport coat’s fabric) and what-have-you.
Of course, the storm tab is meant for extra weather protection when riding or shooting. It can also be found on safari jackets, aviator jackets, and peeking from under the collars very stylish clients of Leviner Wood.