Big Island Weather 2019 | Big Island Hawaii Weather
The weather on the Big Island is more diverse than any island or another comparably sized chunk of land in the world. You name it, we got it. According to the Köppen Climate Classification System (which is probably your favorite system, too, right?), the Big Island has 10 of the 15 types of climatic zones in the world. (Not climactic zones, which we accidentally printed in a previous guidebook. Boy, people were really anxious to find one of those!) Only Cold Continental Climate categories are absent. Here we’ve got tropical, monsoonal, desert and even periglacial climates, among others. So no matter what kind of weather you like, we are sure to have it here. As you ascend the slopes of the volcanoes, you lose about 3 °F for every thousand feet.
Kailua-Kona traditionally has had weather that can best be described as eternal springtime. Quite simply, it’s almost always warm and wonderful. The average high in February (the coldest month) is 80 °F and the low is 64 °F, whereas in August (the warmest month) the high is 87 °F and the low is 69 °F. Humidity is usually between 50 and 80 percent. The temperature change between night and day is greater than the temperature change between winter and summer, so it could easily be said that nighttime is the winter of the Big Island. Balmy wraparound onshore breezes usually keep it comfortable. The exception is during Kona winds (so named because they come from the Kona direction, rather than out of the northeast as is usually the case).
Kona winds occur about 5 percent of the time and bring stillness or warm air to Kona, creating uncomfortably humid conditions. Normal conditions in Kona and Kohala mean clear mornings with afternoon clouds created by thermal heating, so morning is usually better for activities such as air tours. During the summer, evening showers often occur as warm moist air is cooled, squeezing rain out of the humidity. Because it is totally protected from the trade winds by Hualalai, Kona is the only place in the state that gets most of its rainfall in the summer afternoons and evenings. The higher up the mountain, the more rain you get. For 35 years Kona was ravaged by nasty but natural pollutant called vog from Kilauea volcano (thanks to airflow patterns), but with the cessation of volcanic activity in 2018, Kona’s air is now as clean as any part of the island.
Hilo’s weather is almost always described with one word—rain. Hilo is the wettest city in the United States. Annual rainfall is rarely less than 100 inches, usually much more. But rain is not a constant here. Hilo has times of drought like anywhere else. (Like when rainfall was a mere 70 inches one year, triggering rationing.) Most of the rain falls at night. When daytime showers do occur, they are often intense but short-lived. That said, rain or cloudiness will be a factor here. One of the reasons that Kailua-Kona is so much more popular than Hilo is that visitors like sunny weather, and Hilo can’t compete in that area. Also, all that rain has to go somewhere, which is why the ocean off Hilo is not nearly as clear as Kona’s runoff-free waters.
The Kohala resort area is the driest part of the island, with rainfall usually around 10 inches per year. Sunshine is almost assured (which is why it is so popular). The weather penalty here is the wind. As the lava fields heat up during the day, the air heats and rises. Air from the ocean rushes in to fill the void, creating strong afternoon convective breezes. The hotter, drier and sunnier it is that day, the breezier it may be that afternoon.
The general rule of thumb is that in wet areas like Hilo, most of the rain falls at night and early morning. Dry areas like Kona and Kohala get their rains in the late afternoon and early evenings.
Water temperatures range from 75 °F at its coldest in February to 82 °F at its warmest in September/October. It’s colder in some areas where freshwater springs percolate from the ocean’s floor and float to the top, forming a boundary called a Ghyben-Herzberg lens.