Temperature in Oʻahu
Oʻahu has a sub-tropical climate with only two seasons, a hot-to-humid summer (May-Oct) averaging 85°F (29°C) and a cool-to-mild winter (Nov-Apr) averaging 77°F (25°C). Temperatures drop by 10°F (12°C) at night. Ocean temperatures are consistently warm around 77°F (25°C).
*1°F (Fahrenheit) = -17.22°C (Celcius). An easy way to go from Fahrenheit to Celsius is to take 30 off the Fahrenheit value and then half that number, or for 100% accuracy, subtract 32 and divide by 1.8.
Rainfall on Oʻahu
Expect rain showers in winter, however long periods of rain are uncommon.
Leeward vs. Windward
The West Coast (Leeward) has a warmer climate making it drier with light vegetation. The East Coast (Windward) features mountain cliffs and it naturally gets more rain making it more lush and tropical. The South Shore is known for sunshine.
Certain pursuits on Oahu are seasonal. Surf the biggest waves in Nov-Dec, watch for humpback whales from Dec-Apr, pick a Halloween pumpkin in Oct, and catch the best fish Jun-Aug. Hurricane season runs Jun-Nov, but they are rare (the last major one to hit land in Hawaii was Hurricane Iniki in 1992).
Box Jellyfish Calendar
Attention Hawaii beach-goers! Box Jellyfish are known to appear on Oahu’s south shores about 8-10 days following the full moon. Luckily, Waikiki Aquarium keeps a tab on “high probability” dates with a Box Jellyfish Calendar so visitors can check when to be cautious.