March is the tail of the dry season. The trades are still offshore in the mornings and the sky is still clear, but the north swell that carried January and February has faded and the south swell has not started. That is why March is the low point of the year, alongside April and November.
That leaves a coast doing exactly one thing well: small, clean, warm water at 29°C, and long empty mornings on the Nicoya beach breaks. It is a bad month for a surf trip built around swell and a good one for a trip built around getting in the water every day.

