April ends the offshore season and opens the swell season, and the overlap is what makes it worth knowing about. The trade winds weaken through the month, the rains have not properly started, and the first pulses generated deep in the Southern Ocean reach a coast that faces almost due south.
That combination does not last. From May the rain arrives and the wind becomes ordinary, so the groomed mornings that produce Panama's famous figures are behind you and the size that the country page calls the season is ahead. April is the fortnight where both are half true.
The water on the Venao side is climbing back off its March floor, at 27°C, and Santa Catalina is holding at 29.5°C, still the warmer of the two gulfs by a margin that closes fast from here.

