<p>Weather-related delays are a significant challenge in construction projects, particularly in countries like Vietnam, where weather conditions are increasingly unpredictable. This study aims to develop a predictive model to estimate construction schedule delays caused by abnormal weather conditions during the dry and rainy seasons. An eight-step research framework was employed, combining historical meteorological data and records from 15 completed construction projects. Expert evaluations identified extreme temperature and precipitation as the primary causes of delay. Using regression analysis, the study developed two reliable seasonal delay prediction models, achieving R² values of 80.2% for the dry season and 96.0% for the rainy season. Monte Carlo simulations were conducted to assess uncertainty in the forecast, indicating estimated delay probabilities of 84.3% during the dry season and 69.8% during the rainy season. The findings confirm that adverse weather significantly affects project timelines, especially during the structural construction phase. The proposed model provides a practical tool for construction managers to anticipate and mitigate the impacts of inclement weather on project schedules.</p>