A Case Study of Nocturnal Rain Showers over the Windward Coastal Region of the Island of Hawaii

Abstract

Abstract Nocturnal rain showers over the windward side of the island of Hawaii were investigated from the late afternoon of 2 August to the early morning of 3 August 1990 during the Hawaiian Rainband Project (HaRP). Three types of rainbands produce rainfall peaks over the lowland/coastal region during the evening, after midnight, and along the coast in the early morning. In the early evening, an inland rainband develops over the lower slopes as a result of orographic lifting and low-level forcing along the drainage front. As the drainage front progresses toward the coast, new rain cells continue to develop along the drainage front. These cells move westward with the trade winds aloft and dissipate. After the drainage front moves to the Hilo coast, new cell generation along the drainage front ceases. It appears that in the absence of orographic lifting, the shallow (∼0.2 km) katabatic flow offshore is not deep enough to lift the low-level air to saturation. Thus, the rainband weakens and dissipates. It las...