The Goan tourist season runs from late October to early April. Skies are clear, the sea is calm, and beach shacks operate full-tilt. December and early January are peak — accommodation prices double or triple and the beach gets crowded with Indian and foreign holidaymakers.
February and March are the sweet spot: warm, sunny, fewer crowds, and shacks still open. The Carnival in February is worth timing a trip around if you are anywhere near Panaji.
The monsoon (June to September) shuts most of Candolim down. The shacks are dismantled, the sea is too rough to swim, and most restaurants close. The landscape turns electric green and prices drop, but unless you specifically want to see Goa in the rain, plan around it.
April and May are very hot and humid but still dry — a marginal shoulder season with lower prices than the peak months.