Squalls in sea off coast of Japan and their effects on marine operations based on weather observatory data at remote islands

摘要

AbstractSqualls are sudden changes in wind conditions. They are attracting increasing attention in ocean development in tropical regions such as West Africa, which are not hit by typhoons and hurricanes, when designing the mooring systems of floating production, storage, and offloading facilities. In general, a squall may not be very strong and may only last for a short time. Hence, it has not been considered a hazardous design condition for ships, offshore structures, and mooring systems in such regions. However, because of its unpredictability and suddenness, a squall can pose a threat to marine operations that require a fairly calm sea state. In this study, we conducted a questionnaire survey of experienced offshore workers in Japan to clarify the potential risk to marine operations from squalls. Then, weather observatory data for more than 10 years at remote islands were investigated to identify the occurrence of squalls in the sea off coast of Japan. The results suggest that mid-latitude squalls have different characteristics of time evolution to those documented in West Africa. An extreme value analysis of the peak wind and rate of wind change were conducted to quantify the possible magnitudes of squalls.