The Cook Islands have two seasons. The dry season runs from May to October, with temperatures around 24–26°C, lower humidity, and relatively little rain. This is when the islands are at their most comfortable and the water is calmest — ideal for snorkelling and diving. It is also peak tourist season, especially June to August, when prices are higher and the best guesthouses fill up quickly. Book ahead.
The wet season is November to April. Temperatures rise to 28–30°C, humidity increases, and tropical showers become frequent — though they are often brief. This period carries a small risk of cyclones, mainly from December to March. The tradeoff is significantly cheaper accommodation and quieter beaches. The islands don't become inaccessible in the wet season; you just accept that some days will be grey and drizzly.
The shoulder months — April, May, September, and October — offer the best balance: decent weather, reasonable prices, and smaller crowds.
Humpback whales pass through Cook Islands waters between July and October and can often be spotted from the Rarotonga foreshore or on dedicated whale-watching trips.
Te Maeva Nui, the country's biggest cultural festival, runs in late July through August 4th (Constitution Day) and is worth building a trip around if the dates work. Flights and accommodation fill up fast around this time.
Sundays are quiet throughout the year by local custom and law. Many businesses close, transport reduces, and a peaceful hush settles over even Rarotonga's usually busy strip. Plan ahead for food and supplies.