As part of the research aimed at elucidating the cause of low tea yields in the first crop in southern Japan, the relation of climatic conditions to winter bud dormancy was investigated using mature ‘Yabukita’ (Camellia sinensis (L.) O. Kuntze) plants at the Makurazaki Station (N 31° 16.1´) of the National Institute of Vegetable and Tea Science (NIVTS), Japan, as a model. The number of days required for flushing (RDF), when winter tea branches were kept under optimal artificial conditions (25°C, 14-hour daylength and 80% relative humidity), was used as an indicator for expressing the degree of winter bud dormancy. RDF was well predicted by the model [-aT-bD+c (T: mean temperature, D: daylength and a,b,c: parameters)] with the lowest standard error (1.71) and the lowest value of Akaike’s Information Criterion (AIC = 124.06). The simulation of winter bud dormancy indicated that tea grown in Okinawa located in the southernmost region of Japan (N 26° 13´) is highly susceptible to sudden flushing during winter. The results suggested that urgent measures should be taken to alleviate low tea yields in the first crop in southern Japan.