The best times to visit Erwin are late spring (April to early June) and autumn (September through October). Spring brings reliable water levels to the Nolichucky, which is the prime season for whitewater rafting — by midsummer, drought can reduce flows enough that outfitters divert trips to the Watauga River instead. The Appalachian Trail through-hiker crowd peaks in April and May, when northbound hikers resupply in town.
Autumn is arguably the stronger of the two seasons. The Unaka Range puts on a full-scale hardwood color display from early October through early November, the crowds are thin, and cooler temperatures make the mountain hiking far more pleasant than July. The Nolichucky can run well in autumn after good rainfall.
Summer is humid and warm, useful if you are primarily here for the river and have confirmed water levels with an outfitter before you arrive. Winter is quiet — the iron furnace ruins are actually easier to see with the undergrowth down — but there is little organized outdoor activity and the mountain roads can be icy.