View looking north toward the Kahola Mountains on the Big Island of Hawaii.  The trade winds are blowing from right to left.  Notice the classic cloud formation on the windward (right) side of the Kahola Mountains as the geography causes the moist air to be lifted upward and, consequently, cool to temperatures below the dewpoint, thereby creating the condensation observed.  The leeward (left) side of the Kahola Mountains is clear because the descending air is now dry after having lost its moisture in the form of rain on the windward side. 

The Big Island of Hawaii boasts 11 out of the 13 world climates (according to the Koppen classification system) lacking only the Polar Wet and Dry, and the Polar Desert.