Weather is probably a major factor when you plan your trip to Nagasaki, 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 10°C. The rainiest months in Nagasaki are June, July, August and May, with each month seeing an average of 389 mm of rainfall.