Goa runs a strong tourist season and a quiet rainy one — Panaji feels like two cities depending on which you visit.
High season (November–February) is the peak: warm, dry days, comfortable nights, the beaches packed, the Goa Carnival in February, the International Film Festival of India running through late November. Hotel prices are highest, especially over Christmas and New Year.
Shoulder season (March–May) is hot, humid, and pre-monsoon — temperatures into the high 30s, the air heavy, the beaches still busy but cheaper. Easter celebrations through Holy Week are worth timing for if you are interested in the Catholic side of Goan life.
Monsoon (June–September) is the off season — daily torrential rain, the Mandovi running brown and fast, most of the beach shacks dismantled, half the hotels closed. The countryside turns spectacularly green; the food is at its richest. A genuinely different (and underrated) Goa.
October is the bridge — the rain easing, the green still fresh, the cheaper hotel rates still in effect. The best month for a traveller looking to avoid crowds.