The safety and efficiency of air traffic are significantly affected by adverse weather. This holds especially in terminal maneuvering areas (TMA) where, in addition to the impact of weather itself, potential weather avoidance routes are strongly restricted by air traffic regulations. A weather avoidance model DIVMET has been developed which proposes a route through a field of developing thunderstorms. Air traffic control regulations have not been included in it at this stage. DIVMET was applied to the TMA of Hong Kong International Airport as air traffic control (ATC) there has become interested in improving the controller’s work load, especially for managing incoming traffic by avoidance route simulations. Although visual inspection of simulated avoidance routes by ATC was satisfactory, a quantitative validation of simulated with real observed routes was also carried out. Two real adverse weather situations with thunderstorms within the TMA of Hong Kong and with heavily distorted traffic were chosen. The main objective prior to any validation, however, was to identify routes which are solely impacted by weather but do not show any signs of regulation. Route selection was done on the base of flight position data. Landing flights were selected and deviations from standard approach routes were analyzed. As a result, the majority of 272 flights were found to be affected by both weather and regulations (60%), highlighting the challenge for air traffic controllers to manage landing traffic under adverse weather conditions safely and efficiently. Only a few weather-affected flights (7%) were not regulated and could be used for validation. DIVMET simulation routes were presented to local air traffic controllers who confirmed them as potential and realistic avoidance routes. DIVMET weather avoidance route simulations within a TMA appear to be helpful but further model development has to incorporate traffic regulations, to include holdings, short-cuts, and slow-downs. © 2016, Zhejiang University and Springer-Verlag Berlin Heidelberg.