The short answer
May, June and September. Those three months give you the driest weather Northern Ireland offers, daylight that runs to nearly ten at night in midsummer, and none of the July and August pressure on the Causeway car park.
If we had to pick one, June. The Causeway at eight in the evening in June, with the light coming in flat off the Atlantic and nine other people on the stones, is the best hour on this coast.
Month by month
Belfast weather is milder than Americans expect and wetter than the forecast implies. It rarely freezes and it rarely gets above the mid seventies Fahrenheit. What changes month to month is daylight and crowd, far more than temperature.
- January to March
- Dark and quiet. Good hotel rates, and the museums and bars are at their best. The coast is dramatic but the daylight runs out by five.
- April
- Improving fast. Gardens open, the Coast Road is empty, prices are still low. Our under rated month.
- May
- One of the two driest months. Long light, gorse in flower on the Glens, and no crowds yet. Excellent.
- June
- The best month. Daylight until nearly ten, dry, and the Causeway is workable late in the evening.
- July
- Busy, and the Twelfth of July week closes roads and businesses. Book around it or embrace it knowingly.
- August
- Peak visitors and peak Causeway queues. Fine weather, but every attraction needs booking.
- September
- The value month. Warm sea, thinning crowds, prices dropping, and the light turns golden on the coast.
- October to December
- Short days and real weather. Belfast itself is excellent, the Christmas market at City Hall is genuinely good, and the coast becomes a two hour window rather than a day.
The Twelfth of July, explained
Around the eleventh and twelfth of July, Northern Ireland marks the Twelfth with bonfires and parades. It is a major cultural event with a contested history, and for a visitor it means road closures, some businesses shut, and a city that is either fascinating or difficult depending on what you came for.
We do not tell people to avoid it. We tell people to know about it. If you want to understand Northern Ireland it is instructive. If you want a relaxed city break with easy taxis, move your dates by a week.
Daylight, which matters more than weather here
Belfast sits at 54 degrees north, further north than Calgary. In late June the sun sets close to ten at night and there is usable light after that. In late December it is dark at four in the afternoon.
That single fact should drive your dates more than the rain forecast. A June day gives you sixteen hours to work with, which means the Causeway after dinner and the Coast Road twice. A November day gives you seven, which means one thing well and nothing else.
When to book
For June to August, book hotels by February. Belfast's supply of genuinely good rooms is small and the Causeway Coast's supply is smaller. The Bushmills Inn and the Culloden fill first.
Restaurant bookings two to three weeks out for weekends is enough, except around the Twelfth and the big SSE Arena dates, when the whole city tightens at once.