Meteo Ayutthaya in agosto

Thailand's forum is consistent that June sits in a relative lull between the wetter bookends of May and September - it's still hot and humid nationwide, and Ayutthaya specifically gets called out as brutal around midday, but the rain itself is usually a shower rather than an all-day event. Forum regulars who visited Ayutthaya in June had a genuinely good time, describing it as hot and humid with manageable showers rather than a washout. The advice that comes up again and again is to tour the temple ruins early in the morning and save the hottest hours for indoor breaks.

Forum posters describe December as highly predictable and among the most pleasant months across central Thailand generally, with hot daytime temperatures (commonly reaching into the low 30sC), clear skies and minimal rain, while evenings cool into the low-20s or even high-teensC - genuinely comfortable by regional standards. This makes December squarely inside Thailand's cool, dry high season, good conditions for exploring Ayutthaya's outdoor temple ruins on foot without the wet-season rain risk. The clear tradeoff posters note for the broader region this time of year: December is also peak tourist season, so popular sites and accommodations get busy and should be booked ahead.