Torrevieja has one of the sunniest and driest climates in Spain — officially among the driest spots in western Europe, with an average of around 320 sunny days a year and annual rainfall well under 300mm. This means the town works year-round in a way that most beach resorts do not, and the large northern European expat community is partly here because the winters are genuinely mild rather than merely tolerable. January and February are pleasant for walking the lake circuits and the promenade without crowds; spring sees the salt lakes at their most photogenic as algae populations build. There is no truly bad time to visit.
July and August are the busiest months by far. The summer population swells enormously, the beaches are packed, restaurant queues form, and prices rise. If you want the coast at its liveliest — beach bars, evening paseos that run late, the festival atmosphere — this is when to come. The Habaneras Festival takes place in late July and early August, which is worth timing a visit around.
April to June and September to October offer the best balance: warm enough for the beach (water temperatures reach 24°C by September), empty enough to walk the lake paths in peace, and good conditions for seeing flamingos and other wading birds at Laguna de La Mata. October is particularly good — the summer crowds have gone, the light is excellent, and the sea holds its warmth.
November to March is quiet and inexpensive. The town does not shut down the way some resorts do — the permanent population is large enough to keep things running — but choice narrows. For walking, birdwatching, and seeing the lakes without company, this is the time.