(1) L and K are so small, in the rainshadow of the East M volcano and the West M Mountains, that they do not really benefit from the cool northeast T winds and the moisture they bring. In those cases, you couldsay the entire island--or nearly so--are leeward.K on the other hand seems to be mostly windward. The shorter volcanoes (on M, O, K) get so much rain that they have swamps near the summit.The taller volcanoes have dry summits, since they are higher than most rainclouds. They do sometimes get snow in very turbulent KN storms, with tall clouds, which also dump rain over the lower elevations and create flash flooding. The taller volcanoes have dryer leeward sides as well, but even the leeward side can get soaked in a KK storm.
(2) You can judge for yourself by looking at maps that show the highest point of the island (or better yet, Google Earth where you can check "T" and use the shift key and the scroll wheel to make the mountains pop out) and space photos of the entire island.
(3) When you look at aerial photos, note the date. Green vegetation may extend to O's Diamond Head in January, but retreat to the back of the valleys by the end of summer.
(4) Leeward destinations include Hawaii's KK-K and K; M's K, W, L, and K; L City; M's K and the entire west end; O's W, H and to a greater extent, N, W, and M; K's P and W C. Windward destinations include Hawaii's H; M's H and W; M's east end from K to H; O's K and K; K's HB.
(5) The large photo linked below shows the boundary between leeward and windward sides that extends from the highest point on M (K, hidden in clouds in this image) and the southernmost point on M (just to the right of this image) near KG.Near the shore is a two-lane highway, some landscaping watered by the county water system (which brings water down from K by aqueduct, basically), and a lot of k, also known as mesquite.