The Hawaiian Islands are widely recognized as a tropical vacation paradise with beautiful beaches and scenic terrain. Less well-known is that the climate in Hawaii can vary greatly depending on location. I'll use the island of Oahu as an example.

Hawaii lies in the subtropics, where the dominant wind flow is from the northeast - the so-called "trade winds." After blowing over a long stretch of ocean, these moistened winds rise up the eastern, or windward, slopes of the mountains that guard the northeast side of the island, forming clouds and plenty of rain. The green in this high-resolution satellite image signifies an abundance of vegetation resulting from the enhanced rainfall.

Those winds then descend the opposite, or leeward, side of the mountains, where they dry out, leading to much less precipitation, less vegetation and a browner color in this image. In fact, Honolulu, on the leeward side of the mountains along the southern shore of the island, averages only 22 inches of rain a year, just about half of what we average here.