Extreme winds can lead to extreme storms, which are among the most frequent forms of extreme weather in Indonesia. With climate change predicted to increase the adverse impact of extreme weather, it is crucial to keep track of and gauge the severity of storm events. Storm Severity Index (SSI) can be used to measure the severity of storms, which is defined by their intensity, duration, and extent. SSI has been used in continental areas. However, the application of SSI in the maritime continent is still limited. This study explores the application of SSI to measure extreme storms in Indonesia based on wind gust speed. This study uses wind gust data in 1959-2021 from ERA5 reanalysis data and calculates the SSI based on the 98th percentile and the 50-year return value of the wind data. This study also explores the meteorological events that coincide with high SSI values. This study found the SSI able to capture high wind gust events in Java Island. This study finds high SSI value coincides with tropical cyclone events in the Indian Ocean. Topography affects the area on Java Island that has a high SSI value. Further study should evaluate the impact of the coastal and non-coastal areas to reduce the significant effect of sea-land breeze or mountain-valley breeze. In addition, future research also needs to address the significance level of the duration of events in a severe storm to enhance the information on severity.