Pretty much the same as in summer with maybe long pants and a sweater if it gets cold. I remember sweltering Decembers and cold Januarys. Sometimes when it stormed in winter, it might get into the 50's. Not sure with climate change how Hawaii is affected.
Thanks to warm daytime temperatures and just as warm ocean waters, winter in Hawaii is the same dream vacation as summer in Hawaii. The average daytime winter temperature sits around 78°F. Compare that to the average daytime summer temperature of 85°F, and most won't even notice the difference.
Hawaii weather is warm and humid, with temperatures between 70ºF to mid 80ºF and the pleasant trade winds. Even so, you'll need pack at least one pair of long pants and a light sweater.
Take a light jacket or sweater, but chances are you won't even wear that. Of course, if you're planning to stargaze atop Mauna Kea volcano or see sunrise at the summit of Haleakala, you'll need heavier attire because it can dip below the 30s Fahrenheit there.
Hawaii has semi-tropical weather. Temperatures usually range from 75-90 degrees year round in the daytime, and 70-80 degrees at night. Temperatures in the winter months may be a little cooler, where nighttime temperatures can sometimes fall into the 50's.
Pacific Ocean temperatures on Honolulu shores are warmer than those of Hilo, but both are still swim-worthy at 77 and 73 degrees, respectively. Ocean temperatures in December all around the Hawaiian islands rest comfortably at about 77 degrees.
August is the hottest month in Hawaii with an average temperature of 27°C (81°F) and the coldest is January at 23°C (73°F) with the most daily sunshine hours at 11 in July. The wettest month is November with an average of 124mm of rain.
While you may need a light sweater or light jacket in the evenings during your trip, Hawaii's high humidity and sunny, pleasant temperatures create the perfect beach weather to swim and get some sun.
Pack versatile clothing that you can mix and match, and dress up and down. Leave your denim at home! Denim feels so hot and bulky in the tropics. You will be much more comfortable in cotton or linen shorts or pants.
It can be breezy on the beach in the evenings, you might want a light sweater then if you're someone who runs cold. Otherwise you'll only need warm stuff if you're going to the higher elevations like Volcano National Park, the big Maunas, Haleakala, etc.
You'll want to bring a light jacket or sweater; evenings can be cool. Rain probably won't be an all-day affair, but the north shore will certainly be cooler, and it gets more rain in winter. South shore should be warm and sunny. For swimming in winter I wear the equivalent of a short-sleeve rash guard.
A typical December day in Hawaii sees temperatures sitting in the low 80s. December is one of the best times to see poinsettias in their natural habitat. The evenings can get a little chilly, and it is not uncommon to see the temperatures dip into the upper 60s.
Hawaii itself is around 80 degrees year-round so you likely won't need these to wear there, except for maybe at night. Every single indoor place in Hawaii is air conditioned excessively which is why sometimes jeans are helpful!
Beach TowelYou definitely need to bring a beach towel on your Hawaii vacation, but not just any old towel will do! When packing for Hawaii, you'll want to bring a sand-resistant beach towel or blanket to lounge around on. For drying off, I suggest a quick drying microfiber towel. Leave all other bulky towels at home!