Sounds like PO only put on 1 coat for eye candy. Just guessing without photos.
Humidity is not an issue this time of year. You could apply 2-3 coats of Epifanes Rapidcoat per day. Final coat of gloss. Sand each morning with 220.
If the transom is down to bare wood and is permeated with moisture, varnish will not stick. Wait til the fall.