Weather is probably a major factor when you plan your trip to Kosai, but bear in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually August and July, with an average temperature of 25°C, while the coldest months are January and February, with an average of 8°C. The rainiest months in Kosai are July, June, September and October, with each month seeing an average of 293 mm of rainfall.