Folks who visit Rarotonga during winter may end up saying things like this: 

"The thing that was most surprising and unexpected was the weather, a cool front blew in a day after arrival and it was cloudy thereafter, and for the last 2 days, stormy and actually quite cool...as in stay in your room type weather, not tropical at all."

For the most part, winter-time in the Cook Islands offers a wonderful respite from real winter weather around the Southern Hemisphere.  This is when most Kiwis and Aussies venture off to tropical isles to seek warmth and reoutdoors relaxation mid-year.  Temperatures range from the low to mid 20 C, without the humidity of summer-time.  Nights can become cool (it's winter afterall).  Pack a light pullover or cardigan for nighttime dining, strolling etc.  Swimming is refreshing, although sea temps are nowhere near as cold as they would be in temperate zones.  Expect to see some glorious sunsets from the western side of Rarotonga.  Cheers everyone!