January weather forecast for Arutanga, Cook Islands. January through April, with an average sea temperature of 28°C (°F), are months with the warmest. In the Northern Cooks Islands, temperatures are fairly constant throughout the year, while in the Southern Cooks Mangaia in the south is the coolest island; Penrhyn and Rakahanga in the North are the hottest as Jan Feb Mar Apr May Jun. Even during the summer months of January and February, the high temperatures on Rarotonga average a comfortable 84°F (29°C), although there can be hot. Dianz 4, forum posts. When hunger hits, it's just a short stroll to beachfront dining at Sandals Restaurant, or to refresh with a tropical drink at the Barefoot Bar. If January is the only time you can go, then go ahead. Jump to forum. Fernsie cook islands weather in january, forum posts. While Aitutaki island experienced Cyclone Pat in FebruaryRarotonga only caught the effects of a strong breeze. See All Rarotonga Conversations.