May is hot and you should expect temperatures in the high 30s°C in most of the main touring regions. The month is still largely dry, but as the month develops you can expect a few heavy showers to develop ahead of the rains in June. These will bring a welcome respite from the heat and temperatures will start to drop towards the end of the month.
May is a great time to travel if you want to take advantage of lower airfares and room rates and explore Myanmar without the crowds.