There’s a long-running joke in Hawaii that if you don’t like the weather, give it fifteen minutes. As with all axioms, there’s a bit of wisdom mixed in with snark. We enjoy sunny skies about 85% of the year, and because most rainfall blows in on the prevailing trade winds, showers tend to be relatively short-lived.
Of course, the valleys of the Koolau and Waianae mountain ranges see much of the rain that falls on Oahu (similar topography on the Neighbor Islands creates similar conditions). Warm, moist air gets pushed into higher altitudes, condenses into clouds and sometimes falls as rain. Now and again a wet weather system will settle in over the islands, but even then, it’s rarely more than a couple of days of damp weather. (Although many residents will remember 42 consecutive days of rain that fell, soaking everyone and everything and causing widespread flooding 15 years ago.)
With those brief cloudbursts over the mountains come brilliant, almost brash rainbows, and lots of them. And during the winter months, rainbows can be even more abundant. This is because although the days are shorter, the sun moves further east in the afternoons until the winter solstice. This means that west-facing valleys receive more direct sunlight, so when the rain does fall, particularly in the afternoon, rainbows pop up as though they are being farmed by the island itself.