Locals can easily be careless about weather; if the monsoon season doesn't normally started at near the end of June, then I can see the conversation being "norm

Locals can easily be careless about weather; if the monsoon season doesn't normally started at near the end of June, then I can see the conversation being "normally it doesn't rain around this time. It should still be fine to go in." I won't argue that the coach were being careless, though. Disclaimer: my mother is from the region (Mae Chan is only few kms away from the cave, which is in Mae Sai) and she wasn't surprised with the fact that they went in.