My experience here in coastal Songkla province.
The easterly winds die down on the second half of April.
Rains stop around the end of Jan. though.
Late Apr-early May the transition happens but the SW monsoon is a total dud here on the coast.
Hat Yai and inland areas way more rainy.
Bottom line..enjoy the easterly breezes...they keep us cool-ish when the rest of Thailand is boiling.