Coastal Tourist destinations need to adapt to climate variability and change to maintain their tourist competitiveness and attractiveness. Knowing the climatic potential of the destination's activities and managing the location's natural resources is crucial. The last decades have seen advances in climate services for multiple fields. Despite this, there is little research on optimal days for different sea leisure-based activities around the central-western Mediterranean. The present research explores, through a co-creation process with local agents, how the met-ocean conditions influence the activities. Capitalizing on the stakeholders' insights, we defined the concept of "optimal day" and calculated their expected frequency for the specific activities identified by the stakeholders. Our approach puts the ocean's hourly wind and wave data in service using the SIMAR numerical model owned by Puertos del Estado. It transforms them into structured and actionable information for Sea-Based Leisure Activities (SELAs from now onwards). By computing the optimal days for each sea-based activity along Tarragona's shore (one of Europe's most important touristic areas), we pilot a methodology for their detection elsewhere. This information is instrumental in facilitating decision-making and defining diversification strategies for tourist activities. Moreover, we highlight the value of co-creation processes as a valuable tool in identifying adaptive measures for climate change.