My guess is that "best" describes the ease and frequency of sighting rainbows. Businger explains this is because orographic precipitation, climate, and clear l

My guess is that "best" describes the ease and frequency of sighting rainbows. Businger explains this is because orographic precipitation, climate, and clear line of sight due to terrain, make it highly likely to spot a rainbow at least twice a day (early morning and an hour or so before sunset), when the sun is 38 degrees above the horizon on either side of the island. This means you should be able to sight a rainbow closer to the windward side of the island in the morning, and another rainbow closer to the leeward side in the late afternoon. When you take all of these factors into account (more are described in the article), Businger's claim isn't so far off. Given the right conditions, is there anywhere else in the world where you can spot at least two different rainbows every day like clockwork?