Newport's climate is among the most equable in the country, but the experience changes a lot by season. April to early June and late September to October are the sweet spots — warm, sunny, the ocean swims well enough by Pacific standards, and crowds are manageable.
July and August are peak summer. Daytime temperatures sit around 24–27°C, water around 18–20°C, and the population of the peninsula multiplies. Traffic on Pacific Coast Highway can be slow on weekends. Book accommodation well ahead and bring a strategy for parking.
November to March is the off-season. Average daytime highs are still 18–20°C, but Pacific storms can bring serious surf, occasional rain and high winds. Whale-watching trips from the Balboa Pavilion operate from mid-December to mid-April — grey whales pass close to shore on their migration to and from Baja.