The effects of the island of Hawaii on offshore rainband evolution

The diurnal cycle of airflow on the island of Hawaii and the structure of the low-level flow separation line between the island-induced offshore flow and incoming trade winds are reasonably well understood. The formation and evolution of nocturnal and early morning rainfall on the windward side of the island were found to be related to four major factors: (a) the existence or absence of trade wind cloud patches arriving from the northeast Pacific, (b) the effect of island blocking on the trade wind flow as it approaches the island, (c) the low-level convergence and thermal and moisture stratification near the flow separation line, and (d) the position of the flow separation line, controlled by both the Froude number and diabatic processes (nocturnal radiative cooling and evaporative cooling) occurring over the island.