Sea breezes at Cotonou and their interaction with the West African monsoon

5-year 3-hourly wind speed and direction, air temperature over land and sea surface temperature data are analysed in order to characterize sea breezes at Cotonou (Republic of Benin, West Africa). A set of criteria based on the diurnal reversal of wind direction, the thermal gradient and the number of sunshine hours is used to identify sea breeze days. Statistics are presented that describe the occurrence, duration and strength of the sea breezes. It is found that the sea breeze occurs during all seasons in this region.Sea breeze occurrence is found to be strongly influenced by the West African monsoon. The frequency of occurrence shows clearly two regimes characterized by two maxima (December and May). Sea breezes occur about half of the days during non-monsoon season (winter). Land/sea breezes onset and cessation times show a pronounced seasonal variation. Sea breeze strength is greater during the West African monsoon season.A hodograph analysis reveals the existence of both clockwise and anticlockwise rotation. Average hodographs show clearly the onshore-offshore nature of the sea breeze circulation, but have indeterminate rotation. There is a significant seasonal effect of large-scale flows on sea breeze hodograph patterns.