At the latitude of the Hawaiian Islands the trade winds prevail from the northeast. These trade winds are generally stronger during the summer months and increase from morning to afternoon, as the sun heats the air. As the moisture-laden air contacts the northern sides of the islands it is forced up by the grade (orographic lifting), expands, cools and forms clouds. While the air drops much of its moisture during its ascent of the northern slopes its descent of the southern slopes, compresses, heats and clears that air with an increased capacity to hold moisture. This is why the verdant rainforests lie on the northern sides of the islands while the southern sides favor dependable sunshine and resorts.