Gena1480 wrote:i want to write Wat Pah Nanachat
and ask permission if i can stay there for a month.
and what date is best to fly there.
Yes just write the guest monk, he can inform you what time of the year would be best. Usually as far as I experienced many laymen from the west come and go. The maximum time for you to stay in the monastery is one month anyways. After this you either have to leave or you "ordain" as an Anagarika. Depends if the monastery thinks you are suitable.
All this is based is on my experiences 10 years ago, so it might be different today.
For the weather I'd suggest you go there in November, December... it's not to hot then. But this info any other available Thailand-Travel-Guide might grand you.