What to do if our visa exemption is ending on Sept 30 and we're planning to leave by train for Nong Khai tomorrow but the flood water is bad in Phra Khanong?

If you're unable to leave Thailand immediately, consider using a ride-hailing service like Grab to get to the airport or a land border crossing.

You still have two days to exit Thailand, which should give you plenty of time to catch a flight out. There are multiple bridges available for crossing into neighboring countries.

The fine for overstaying in Thailand is 500 baht per day, with a maximum of 20,000 baht. This fine is payable at the border when you leave the country. Additionally, re-entry bans can be imposed after 90 days if you exit on your own. Leaving a day or two late can cost between 500 and 1,000 baht. Alternatively, you can opt for a one-time 30-day extension, which costs 1,900 baht and can be obtained at any immigration office. However, I couldn't find any information on a flood-related grace period announced by immigration. For train services, you can contact the SRT call centre at 1690 or check the website ttsview.railway.co.th to see which services are running.

Considering the time available, it doesn't seem like there's a pressing issue with leaving Thailand. You should have plenty of time to catch a flight out.