The closer you get to the equator the more tropical the conditions with countries like Papua New Guinea, Tonga and the Solomon Islands experiencing their rainy season from December through to March.
The heat in Northern Australia is quite intense around the start of the year, with really oppressive weather up in Darwin meaning hiking in January is definitely not recommended. Further south in New Zealand however, you'll find relatively mild temperatures with chances to spot orcas, sperm whales and dolphins off Kaikoura, definitely worth adding to a Valentine's itinerary in February.
November to April is cyclone season, particularly along the coastlines of Western Australia, northeast Queensland, Papua New Guinea, Solomon Islands and the islands of the South Pacific. Tropical cyclones can occur at any time of year though, so please keep abreast of regionalised warnings.
April and May are often considered the best time to go to Australia and Oceania as temperatures are starting to dip and rains are felt with a little less consistency in sub-regions like Micronesia and Polynesia.
As the dry season starts in June and July this is a great opportunity to explore more of the continent without heat and humidity; and if you're hoping to hit snow covered slopes in New Zealand, then this is another great time of year to visit Australia and Oceania.
From July to October you can swim with one of nature’s giants in the warm waters around Tonga. Humpback whales migrate here to give birth and suckle their calves, building up layers of fat before making the long journey back down to Antarctica.
August is an ideal month to visit Australia and Oceania for outdoor activities like trekking and mountain biking, although dolphin spotting tours will probably be met with more success in Fiji or Hawaii as opposed to New Zealand or Western Australia.
September into October finds the spring in New South Wales, Victoria, Tasmania and New Zealand whereas Solomon Islands, Papua New Guinea, Samoa and Tahiti will just be beginning their rainiest months.
November and December signal the start of the summer for Aussies and Kiwis with a wide range of outdoor music, arts and foodie festivals pushing up accommodation prices in Melbourne and Sydney whilst adding to the range of alternatives to days spent at the beach.