Severe Thunderstorm Climatology in the Balearic Islands (2010-2023)

This article presents the first climatology of severe thunderstorms (STs) in the Balearic Islands, Spain, between 2010 and 2023. The criteria used to classify severe thunderstorms in the database are as follows: straight-line winds exceeding 90 km/h, hail with a diameter of 2cm or more or a tornado touching the ground. Meeting any one of these three crireria was sufficient for a thunderstorm to be classified as severe. Thanks to severe weather reports, observations from 111 weather stations and additional data sources, an exhaustive database of STs in the Balearics was constructed, including 43 severe thunderstorms affecting the islands during 41 severe thunderstorm days. The database itself is included in this paper, and is accessible to the scientific community, representing the first contribution of this paper. A second contribution is a detailed analysis of the spatial and temporal distribution of STs affecting the Balearic Islands. Annual, monthly, seasonal, fortnightly, spatial and hourly distributions were studied. Autumn accounts for 48.8% of all STs, with the highest frequency observed in October. The fortnightly distribution revealed a peak of 7 STs during the second half of August. Convective straight-line winds were the most common severe phenomena in STs affecting the Balearic Islands, occurring in 41.9% of all cases. The hourly distribution showed a peak between 10:00 and 12:00 AM. In terms of spatial distribution, the highest incidence was recorded on the largest island, Mallorca, with a mean of 2.6 STs per year. The southern region of Mallorca, followed by its central part, emerged as hotspots for severe thunderstorms within the archipelago. The vast majority (84%) of the registered STs in the islands originated offshore. For this reason, another key contribution of the paper is the analysis of the relationship between ST frequency and sea surface temperature (SST) and SST anomalies. For each severe thunderstorm day, the mean SST and SST anomaly in the Balearic Sea were obtained using daily reanalysis at 12 UTC from ERA5. Peak ST activity occurred when SST ranged between 25°C and 26°C. Extremely severe thunderstorms (ESTs), defined by wind gusts over 120 km/h, hail of 5 cm or more, and/or a land tornado rated EF1 or higher, occurred most frequently when SST ranged between 27°C and 28°C.