One thing that doesn't seem to ever really be talked about with Hawaii, is the very unique climate, at least on the Big Island. Hawaii is a unique chain of islands that have been through volcanic action. As such, the islands seem to rise from the water out of nowhere and little to break wind and waves before they reach the islands.
Keep in mind that these are mountains, they rise very rapidly and quite high out of the water. As the wind and air blow up and over these mountains, the air rapidly cools and forms clouds over all of the islands. This helps shape some of the most unique climates I've been through. Driving across to the other side of the island takes roughly 2 hours, no matter which way you take. To completely circle the island, it would take roughly 4 hours in total. Pick any direction and drive, and you will likely pass through 2-3 different climate zones.
The first full day in Hawaii, we drove to Pololu Valley. Now in order to get there, we started out at our hotel in Keauhou Bay, situated in a warm but more temperate zone. This area of the island is often shaded by clouds coming off the largest mountain tops. Mornings start clear and sunny, part way through the day, it becomes cloudy, but rarely rains. It's much like Central New York in the summer, where I grew up, except more ocean.
As you drive north toward the airport, you cross into a desert like area. This area is arid, gets lots and lots of sun, and is marked by huge lava flows from the past. Fields of dead grass, and plains of black stone. This is the most desolate area of the island, there are a number of beaches in this area, but very few houses, or resorts really. There are some remote beaches here that are worth checking out, but beware, the roads to these places require a decent SUV in my opinion, though many people didn't let the rocky roads deter them.
We needed to use the bathroom and took a detour up to Waimea, which is a decent sized ranching town up in the valley between two peaks on the island. Wind blows through this area in between mountains, forms clouds, and rains. This area had an odd but almost constant rain. This was consistent for the entire trip. Any road that cut through the center of the island needed to climb into the highlands, and there was always rain along the way someplace. Due to the lower temperatures at this altitude, it gave a feel of a slightly warmer Seattle area. Temperate with a lot of rain.
After stopping in Waimea, we took a side road along the mountains and down into Pololu Valley. As we descended and approached Pololu Valley, we entered the rain forest area of the island. Tucked up in the valleys of the north side of the Big Island, rain was light but almost constant. Lush green plants covered everything, and the rain would come heavy and leave. Pulsing on and off, the entire afternoon was marked by shifting showers.
Now, I was only in Hawaii for 5 days. That doesn't mean that this was what the climate is year round. It is the one place I've ever been where I have experienced 4 distinct climates within a 2 hours drive. It truly is a unique experience, and one I would love to experience again. The island boasts more areas to the south around the valcano that would characterize a typical rocky mountain slope, paired with low areas resembling grasslands. The town of Hilo falls in the tropical town feel on the opposite side of the island. Really you can see so many different climates, it really will surprise you. If you get the chance, drive the Big Island, it is a varied and interesting place.