A 20-year analysis of disturbance-driven rainfall on O’ahu, Hawai’i

Abstract

AbstractUndisturbed trade-wind conditions comprise the most prevalent synoptic weather pattern in Hawai’i and produces a distinct pattern of orographic rainfall. Significant total rainfall contributions and extreme events are linked to four types of atmospheric disturbances: cold fronts, Kona lows, upper-tropospheric disturbances, and tropical cyclones. In this study, a 20- year (1990-2010) categorical disturbance time series is compiled and analyzed in relation to daily rainfall over the same period. The primary objective of this research is to determine how disturbances contribute to total wet season rainfall on the Island of O’ahu, Hawai’i. On average, 41% of wet seasonal rainfall occurs on disturbance days. Seventeen percent of seasonal rainfall can be directly attributed to disturbances (after a background signal is removed) and as much as 48% in a single season. The intensity of disturbance rainfall (mm/day) is a stronger predictor (r2 = 0.49; p < 0.001) of the total seasonal rainfall than the frequency of occurrence (r2 = 0.11; p = 0.153). Cold fronts are the most common disturbance type; however, the rainfall associated with fronts that cross the island is significantly higher than rainfall produced from non-crossing fronts. In fact, non-crossing fronts produce significantly less rainfall than under mean non-disturbance conditions 76% of the time. While the combined influence of atmospheric disturbances can account for almost half of the rainfall received during the wet season, the primary factor in determining a relatively wet or dry season/year on O’ahu are the frequency and rainfall intensity of Kona Low events.