Beirut has a Mediterranean climate — hot dry summers, mild wet winters — with a mountain range immediately behind it that changes everything within an hour’s drive.
By season
Spring (April–June). The best months. Warm rather than hot, the hills green and full of wildflowers, the sea warming up, and prices before the summer rush. May is close to ideal.
Summer (July–August). Hot — low thirties — and humid, which is the part visitors underestimate. Beirut’s humidity in August is heavy and the nights do not cool much.
It is also diaspora season. Lebanese from the Gulf, Europe, the Americas and West Africa come home in enormous numbers. The country fills, restaurants are booked out, the mountains are busy, the festivals run, and the city is at its liveliest.
That is either the reason to come in August or the reason not to.
Autumn (September–November). The other excellent window. September is still swimming weather, October is warm and clear, and the crowds have gone. Prices drop.
Winter (December–March). Mild in the city — twelve to eighteen degrees — and wet. Beirut gets most of its rain between November and March, in heavy bursts rather than drizzle.
And it snows in the mountains, forty minutes away. Lebanon has half a dozen ski resorts — Faraya-Mzaar is the main one — and the cliché about skiing in the morning and swimming in the afternoon is technically true in March, though nobody actually does it.
The festivals
Baalbeck International Festival (summer) — performances among the Roman temples at Baalbek, running since 1956. Suspended and revived according to circumstances.
Beiteddine Art Festival (summer) — in the courtyards of the palace in the Chouf.
Byblos International Festival (summer) — by the harbour.
Beirut & Beyond and the film festivals through the autumn.
All of these depend on the situation and have been cancelled in some years. Check.
Ramadan and the religious calendar
Ramadan moves through the year on the lunar calendar. Beirut is a mixed city, so most restaurants stay open, but the rhythm changes — quiet days, and iftar after sunset, which produces some of the best eating of the year.
Eid al-Fitr and Eid al-Adha, Christmas and Easter (both Western and Orthodox dates) are all public holidays, and the country effectively stops for several of them.
What actually decides your dates
Not the weather. It is the security situation, and that cannot be planned around a season.
Check the advisories close to your dates, be prepared to change plans, and buy the flexible ticket.
Practical
Bring layers in winter — Beirut buildings are built for heat and are cold and damp in January, and the heating depends on the generator.
Summer: light clothing, and understand that air conditioning depends on the electricity supply. Ask your hotel about generator backup — see where to stay.
Swimming: June to October in the sea, and not off the Beirut shoreline — see the beaches.