Bangkok and north Thailand is presently experiencing exceptionally heavy flooding (due to a wetter than usual wet season plus the effects of a couple of typhoons which dumped even more rain). On average Thailand gets a major flood every two years - this one is particularly bad. If you are poor Thai farmer with little money and no opportunity to get out of the way of the flood, this is a major and life-threatening problem. If you are a relatively wealthy foreign visitor, not so much.
But if you are in Bangkok when the streets flood do take care - you won't believe what you see floating down the street when the sewer system is inundated!
Take care walking in flooded streets, potholes will be invisible and you could hurt yourself if you fall into one.
Limit your travel to rural areas, especially those affected by the floods, the roads will be bad and landslides do occur.
I'd say it's more dangerous than usual, but not unmanageably dangerous - take extra care. The water will drain away over the next week or two and life will return to normal. about 8 years ago