Weather is probably a major factor when you plan your trip to Mornington Island, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually November and October with an average temp of 86°F, while the coldest months are June and July with an average of 76°F. The rainiest months in Mornington Island are January, February, March, and December, with each month seeing an average of 8 inches of rainfall.