Weather in Thailand in July
Hot and wet or hot and dry?
In many ways July is just a continuation of June weather-wise in Thailand. Most provinces see about the same temperature range and the same or slightly heavier levels of rainfall. Except, that is, for Ko Chang and the Andaman coast — both of which see considerable increases in rainfall.
Bangkok and Central Thailand
July marks the beginning of a steady rise in rainfall and very slight drop in daily average temperatures that will continue on a monthly basis through to September. As long as you don't mind the rain, Kanchanaburi is quite good this time of the year as the waterfalls are really going and the national parks are pretty (if muddy and slippery).
If you thought June on Ko Chang was wet, prepare for more of the same in July. Torrential. The especially heavy rain starts to take its toll with erosion and landslides becoming a bit of a problem. Not to say there is no sun at all, but generally speaking, July is an especially wet month on Ko Chang.
July is the first really wet month of the year in Chiang Mai. You'll see some rain more often than not and street flooding will be a problem after heavy downfalls. While the forests will really be coming into their own as far as lushness is concerned, the trekking will be heavy going. You will get wet. You will get muddy. But that's to be expected — you're in a tropical jungle afterall! The provinces bordering Burma along with Chiang Rai in the far north will see even more rain than elsewhere in northern Thailand.
The weather in July in northeast Thailand is pretty much a carbon copy of June — wet and hot! The far eastern province of Nakhon Phanom sees especially heavy rain with the rest of Thailand. While you'll be seeing rain roughly every other day, this remains a reasonable time weather-wise to visit Northeast Thailand.
Expect very similar weather in July as you would in June. Hot and wet, though not as wet as the west coast. The northern stretch of the Gulf Coast, including towns like Prachuap Khiri Khan, Hua Hin and Phetburi will be significantly drier than Ko Samui, Ko Pha Ngan and Ko Tao. Even though there will be rain on the islands in July, there will still be a lot of sun too, and, for dedicated island time, these islands remain your best bet in Thailand weather-wise.
The west coast of Thailand is wet with rough seas in July. Some provinces fare worse than others: Ranong in the north is especially wet, Phuket less so, Trang lesser so and Satun lesser so still, but they're still all pretty wet! Some smaller islands may see a selection of the cheaper guesthouses and resorts shut down or run on a skeleton staff as business drops. Ferry frequency will also be reduced — especially out to Ko Lipe in Saturn province. Overall, for island time, the east (Gulf) coast is better this time of year.