Hey Jay!

Great question! To start (and to start with the most optimistic answer), sea turtles can appear on any beach at any time of year, so the opportunity to see one is always there. That being said, there are known turtle seasons and turtle nesting beaches, which provide a greater likelihood of seeing turtles.

To confirm, you’re not visiting at the worst time of year to see the turtles, but you’re not visiting at the best time of year, either. 🙁 Here’s a rough guide to turtle sightings in Costa Rica:

Ostional Refuge (Nicoya Peninsula): technically May to December, but most sightings occur August to December.
Tortuguero National Park (Caribbean): technically March to October, but most sightings occur July to October.
Las Baulas National Park (Guanacaste): mid-October to mid-March

Since you plan to visit in late-June/early-July, I’d say your best bet to see one would be at the Tortuguero National Park. You’ll be arriving a bit early, but sometimes turtle schedules shift, so it’s possible they’ll come earlier this year. Ostional would be your next-best option, but June/July is still a bit early for the turtles over there. Regardless of where you decide to go, scheduling the turtle-viewing experience as late in your trip as possible (i.e., in July as opposed to June) would be most favorable, if possible.

Pura vida! 🙂