I have 20 days in Thailand before meeting a friend in Vientiane. I will be back in Thailand again later this year so No need to see everything or knock anything off a list , beaches or mountains both sound good , I'm in to nature relaxing, hopefully a good scooter excursion if possible with the weather. Ruins or wats along the way are fine too. The question is where is the weather nice? I don't mind a couple hours of afternoon showers but would prefer not to experience extreme humidity or heat or super crazy tropical storms... Where to go? The islands? the north ? The isan? Any suggestions are greatly appreciated.
Hot and Humid is something you will definitely experience with Thailand. It's a bit cooler in the north and more breeze in the south but again, the raining season is here so you will get to have rain no matter where you go. Check the weather about a week ahead I think that's the best way.
See the Daily Observation Report on the The Thailand Meteorological website. North doesn't necessarily mean cooler. It's 35C outside right now in Chiang Mai, but gets cooler when thunderstorms bring rain in the evening (lately that's been every 2-3 days) or you can stay somewhere at higher altitude then it's down in the mid-20s above 1000m. This time of year it's usually hard to expect clear sunny skies anywhere but your best chance is probably the lower gulf islands, i.e. Ko Samui/Phangan/Tao but being the tropics it can cloud up and even rain on any given day. If you want virtually guaranteed clear skies and less heat/humidity, come back in January.