The Numerical Study of the Tornado-Like Vortex Event in Oahu Island on 8 June 2003

This study re-visits a heavy rainfall event over central Oahu that is reported in 2003 with a rare weak tornado observed. The focus of this study is to analyze the meteorological conditions that led to the formation of the tornado from numerical model data. Previous work primarily focuses on the convection initiation of this case over the semi-arid region using numerical model with 1.5-km grids. An ultra-high-resolution model setup has been utilized to conduct and simulate the tornado-like vortex genesis and movement in this study. The most appropriate grid size is 40m which coupled with the large-eddy simulation (LES) method, successfully reproduces the weak vortex event. This simulation allows for a detailed analysis of the vortex's initialization and downstream movement, demonstrating the effectiveness of the model despite minor discrepancies in the tornado's exact location. The results show that this tornado event was influenced by the interaction between the local land-sea breeze on Oahu, thermally induced convective systems, and topography. Initially, a weak vortex formed near the ground due to the downdrafts of the land-sea breeze and convective systems. Subsequently, the influence of the incoming convective system, through the coupling effect between the upper and lower layers, created a suction effect that enhanced the upper-level downdrafts. This process allowed the tornado vortex to connect from the top to the bottom. The results of this study will aid in improving numerical weather prediction (NWP) models and assisting forecasters in predicting similar weather events over tropical islands