Kailua-Kona has warm weather throughout the year.  High temperatures are between 80 and 85 degrees Fahrenheit, and lows are around 70, with very little seasonal fluctuation.  Lodgings with air conditioning or direct oceanfront are recommended, particularly within the town of Kailua-Kona itself which can have little airflow and high heat indices in summer.  

The Kailua-Kona area has a unique microclimate for Hawai'i, because of its position in the lee of three major volcanic mountains (Hualalai, Mauna Kea and Mauna Loa). While for most of Hawaii, the winter months are generally the rainiest, Kona's drier season is generally from November through March, while the rainy season runs from April through October. However, there is not a striking difference between the two, especially in the area around Kailua-Kona.

Kailua-Kona has more cloudy and rainy days than the Kohala Coast, located approximtely 25 miles to the north, which is one of the sunniest and driest locations in all of Hawai'i. Kailua-Kona is also prone to vog, volcanic smog, a form of air pollution, produced by Kilauea, an actively erupting volcano. Vog can cause health problems in some individuals and also creates obscure, grey, hazy skies. The most commonly reported health effects include headaches, watery eyes, sore throat, breathing difficulties – including asthma attacks, and general lethargy. Vog is less prevalent in most other parts of the island. Vog is not strictly seasonal, but is heavier in Kailua-Kona during the prevailing tradewinds, which blow 92% of the time during the summer but start to diminish in the winter when trade wind activity is only 40% of the time in January.

Ocean temperatures fluctuate about 5-10 degrees between summer and winter depending on location.

The tourist season is traditionally December through March, as people from continental North America come to escape their winter climates.  Expect more crowds and higher rates during this period. However, if you visit in this season, you'll also get to enjoy some attractions that aren't available in the off-season, such as the humpback whale migration.