WRRCTR No.119 Mesoscale Structure of Hawaiian Rainstorms

Abstract

I. Three significant Hawaiian rainstorms were analyzed using conventional meteorological data and photographs from Synchronous Meteorological Satellite (SMS-2). The impact of the satellite on analysis and forecasting was evaluated. Gridding inaccuracies and the distinctive nature of Hawaiian rains limit the impact of the satellite to the scale of synoptic analysis. The storms studied illustrate the range of Hawaiian flood producing systems and the limitations of the detection network. The most important meteorological determinant of flood location is the low-level wind direction. Forecast and detection capabilities are evaluated in terms of developments in the conterminus United States, and it is concluded that the absence of meteorological radar in Hawai'i inhibits significant progress. II. Contingency indices (CI) were computed for 103 rain gages in the Hawaiian Islands. Results are presented in matrices of CI and in individual island maps on which CIs are plotted and analyzed relative to representative stations. The secondary CI maximum with increasing station separation, which has been attributed to spacing of convective updrafts, does not appear in Hawaiian examples. Orography dominates the CI patterns which resemble isohyets. The analysis was extended to interisland comparisons using representative windward and leeward stations. CIs decrease with distance in both samples but more so for windward (trade wind) stations.