We studied the diurnal variation of stratification in Izmit Bay with temperature and current velocity, and investigated the influence of atmospheric conditions. In the east of the bay entrance, 10-min temperature and hourly current measurements were made between the dates of 4 February 2015 and 24 April 2015, down to about 40 m depth in the water column. In addition to this, hourly temperature and salinity with depth data were collected between the dates of 4 and 7 February 2015 by a research vessel. The meteorological parameters for the atmospheric conditions were obtained from the closest weather stations (Yalova, Cinarcik, and Gebze). Thermocline depth varied between 20 and 30 m with instant changes at 6 to 35 m of depth due to strong wind conditions with 3 days of time delay. The south-westerly current directions were found in both layers, but the current speed decayed with depth. The high buoyancy frequency due to strong stratification decreased in strong wind and shear dominated the mixing process. Air pressure, air temperature, north-south component of wind and sea level had a semidiurnal cycle. A high-frequency measurement in a 2-layer system is highly significant to understand, explain, and determine the cause and effect relationships of hydrographic processes.