Orographic effects on localized heavy rainfall events over southwestern Taiwan on 27 and 28 June 2008 during the post-Mei-Yu period

This study aims to perform observational data analyses, including European Centre for Medium-Range Weather Forecasts data, radar reflectivity, rainfall data, and numerical simulations with the Weather Research and Forecasting model to examine the orographic effects on a localized heavy rainfall episode which produced up to 204 and 161.5 mm over southwestern Taiwan on 27 and 28 June 2008, respectively. We found that the continuous inland-transport of moist air or inland-movement of convection from the nearby ocean to southwestern Taiwan occur on both days. The orographic lifting on the moist air and convection generates heavy rainfall over sloped areas on 27 June when the relatively fast southwesterly low-level wind prevails (~ 10 m s−1). The cool air near the foothill facilitates the new development of convection on the upstream side of the old convection over the slope and produces heavy rainfall over lowlands near the foothill. On 28 June, the convection, which is embedded in a relatively slow southwesterly moist airflow, is enhanced over the low-level convergence areas in the lowlands due to the prevailing southwesterly wind. This wind is deflected by the orographic effect and produces heavy rainfall. In addition, the cool air from sloped areas enhances the offshore flow which interacts with the prevailing wind to strengthen the low-level convergence over lowlands and coasts.

► A localized heavy rainfall episode over southwestern Taiwan on 27 and 28 June 2008 was investigated. ► Study the orographic effects on the inland-transport (inland-movement) of moist air (convection). ► The lifting over the sloped areas and the cool air near the foothill are important on 27 June. ► On 28 June, the southwesterly wind and the deflected wind produce a low-level convergence near coasts. ► The findings of this paper may be applicable to heavy orographic rainfall over coastal mountains.