The Cook Islands Meteorological Service has confirmed the chill and the rain is a result of El Nino climatic changes arising from the Pacific Ocean.
Senior meteorologist Ioane Kake told CI News that the changes would affect the weather pattern, bringing in rain and a drop in temperature.
Meteorologists were working on gauging the strength of the El Nino, he said.
El Nino is a phase of the El Nino-Southern Oscillation (ENSO) cycle, which describes fluctuations in temperature between the ocean and atmosphere in the east-central Equatorial Pacific.
It is an irregularly-occurring and complex series of climatic changes.
Effects include reversal of wind patterns across the Pacific, drought in Australasia, and unseasonal heavy rain in South America.
“At this stage it’s too early to detect the strength of this El Nino but there will be some significant impact,” Kake said.
“People need to take caution, regardless of its strength.”
During the El Nino pattern in the middle of last year, temperatures dropped to as low as 14.4 degrees Celsius in Rarotonga in June.
Kake has urged people to keep warm, especially during the night.
He says that in the southern Cook Islands the weather is expected to be cloudy with occasional showers for the next few days.
It is also expected to be particularly cold at night.
“My advice to the public is to keep warm and dry.”