The dry season runs from February through May and is the best time to visit. Trails are passable, rivers are lower, and the weather is reliably good. This is also the period for Carnival (Mas Dominik), held in the days before Ash Wednesday — usually late February or early March — which brings street parties, parades, and calypso competitions to Roseau.
The wet season runs from June through November, coinciding with hurricane season. Dominica's rugged terrain makes it particularly vulnerable to landslides and flooding during heavy rainfall. Hurricane Maria in 2017 demonstrated how serious this can be. Travel is still possible in the wet season and the island is considerably cheaper, but expect trail closures, muddy conditions, and the possibility of disrupted transport. Some hikers prefer the wet season for the lush colours and cooler temperatures; if you go, check conditions locally before heading into the hills.
October brings the World Creole Music Festival, one of the Caribbean's best music events, drawing performers from across the Creole-speaking world — Dominica, Martinique, Guadeloupe, Haiti, Reunion. It takes place over three days in late October and the island fills up. Book accommodation well in advance.
Jazz 'n Creole, held in May at Fort Shirley in Cabrits National Park, is a smaller, more relaxed festival worth catching if you're there at the right time.
December through January is the beginning of another quieter period before the carnival rush. Whale watching — humpbacks offshore — is good from January to March.