Abstract <p>Using long-term studies of the thermal structure of the Black Sea at the Gelendzhik study site, a parameterization of temperature profiles in the active layer was proposed for the warm period (May–November) based on ten-day averaging. It included the variability of the upper mixed layer, its temperature and thickness. The ten-day grouping was performed for all studied years (2010–2023) simultaneously, with only day and month being taken into account, to remove synoptic variability and concentrate on general seasonal dynamics. The averaged temperature profiles were converted to dimensionless form and described as a universal power function of dimensionless depth. With a reverse transition back to dimensional variables, it was possible to reproduce an annual-average temperature profile in the seasonal thermocline for any particulate day from May to November. Assuming the temperature in the upper mixed layer to be the same as at the uppermost part of the thermocline, we were able to reconstruct the thermal structure of the entire active layer. Calculation examples for different ten-day periods are provided, along with comparison of real temperature profiles with the ten-day averaged and formula-based profiles.</p>