Low water temperature during the summer associated with the occurrence of cold water zone off Haeundae was studied using the data from CTD observations and a monitoring buoy deployed in Suyeong Bay. Shortterm variability of current was dominant and was not related to the wind. The NE-SW components of wind parallel to the coast contained more than 96% of total variance and could account for major fluctuations of water temperature. Upwelling-response of water temperature was very sensitive so that the temperature began to decrease immediately after the onset of the southwesterly wind. In particular, there were three cases in which SW winds for only two days caused considerable temperature drops. In 2009, four upwelling events shorter than 5 days took place while seven events with periods of 2~18 days were recorded in 2010. During a very intense upwelling for seven days in mid-August 2010, temperature decreased by more than $10^{circ}C$ in spite of the variable winds. Temperature variability at Gampo, Ulsan, Gijang and Haeundae had similar patterns. CTD observation and satellite imagery showed that the upwelling zone could be extended to the Haeundae-Busan area. According to the wavelet analysis, coherent periods were 2~8 days during the frequent upwelling/downwelling events.