Courtyards are very popular in South China. They are considered to be micrometeorological modifiers and have great impacts on human thermal comfort and building energy consumption. Micrometeorological conditions, including air and surface temperatures, humidity, solar radiation, and wind speed, were continuously measured in both an enclosed courtyard and a semi-enclosed courtyard in Guangzhou on a sunny summer day. The performance of the CTTC (cluster thermal time constant) models with various calculation methods was tested against the recorded data for predicting courtyard air temperature. The results show that the daily courtyard air temperature variations were mainly caused by solar radiation. The solar radiation contribution was overestimated by only considering the radiation absorbed by the ground, and the thermal inertia was overestimated by calculating the cluster thermal time constant with an equivalent method. A new predictive model based on the CTTC model was proposed by integrating the impacts of ground and walls weighted by their surface areas. The performances of the model in the daily mean error, root mean square error and consistency index were determined to be 0.1 ℃, 0.5 ℃ and 0.98, respectively, for the enclosed courtyard and 0.1 ℃, 1.1 ℃ and 0.96, respectively, for the semi-enclosed courtyard. The model is beneficial to aid architects to evaluate courtyard micrometeorological conditions in early design stages.