Rabbits typically molt four times a year (alternating between heavy and light molts). August/September seems to be the big time for fall molts, so it's the right time for winter molting. The difference between molting and shedding is that when a rabbit molts, they shed and regrow their whole coat (may only be a layer of it for the lighter molts, I don't remember exactly). Some rabbits (my Holland, for example), seem to shed a ton all year long.
Some molts are explosive and others are barely noticeable. It varies from bunny to bunny and can vary even within a single bunny. Some bunnies occasionally change color somewhat when they molt. Some molts happen evenly, others look more than a little awkward. In other words, there's no "normal" for molting!
I'm glad you're combing them 1-2x a day! That's crucial during molts, as bunnies can get hairballs the way cats do but unlike cats, they lack the ability to vomit so they often have trouble getting rid of a hairball. A bad hairball can actually be fatal to a bunny if they don't get medical treatment, because it can cause GI stasis.
I swear by my furminator for shedding bunns (I have a lionhead and a Holland lop, two extremely different coat types, and it works wonders on both). Furminators are a bit pricey, but you can often find them on Amazon or eBay for around half what they cost in pet stores and they're amazing (plus they have a money back guarantee in case you or your bunn don't like it). As far as brushes go, wire tipped brushes are a no-no, as rabbits have very sensitive skin - if a traditional animal brush is used, it needs to be rubber tipped.