Hailstorm Events Over a Maritime Tropical Region: Storm Environments and Characteristics

In recent years, the Maritime Tropics (mT) have reported an increase in hail events, including five occurrences over Surabaya, Indonesia. Past studies of mT hailstorms have been limited to individual case studies. A more comprehensive study is needed to improve understanding of hailstorms in this region, and may also provide new insights into the requirements for hailstorms worldwide. This study uses simulations of five recent hailstorms created with the Weather Research and Forecasting Model to evaluate the pre-storm environments, and five additional simulations help differentiate these environments from those associated with storms that lacked hailfall. Compared to other regions experiencing hailstorms, the mT environments exhibit moderate CAPE, much less deep-layer shear, and much higher low-level specific humidity. These environmental conditions typically result in ordinary single-cell, pulse-type storms. The introduction of a new variable, NetCAPE (the net value of CAPE after accounting for precipitation loading and any CIN at lower levels), demonstrates potential in distinguishing hail from no-hail events in the mT. The median NetCAPE for the five hail events is over 40% greater within various depths of the hail growth zone, and when combined with lower near-surface relative humidity and melting level heights, differentiates most hail from no-hail cases.