The Mediterranean Extreme Events Experiment and storm Harry in January 2026

Abstract

Abstract The Global Observing System (GOS) includes drifting buoys with barometers whose surface pressure observations are essential for estimating the current state of the atmosphere and ocean for Numerical Weather Prediction. The Global Drifter Program, a scientific project based at the Scripps Institution of Oceanography, provides the majority of these buoys (barometer drifters). However, regions with sparse in situ observation coverage can limit weather forecast skill. We describe the Mediterranean Extreme Events Experiment (M3E) – a project with partners from Europe and the United States – which, via the deployment of barometer drifters into the data‐sparse Ionian Sea and central Mediterranean, aims to (1) improve the weather forecasting of extreme events, (2) understand cyclone development across the Mediterranean, and (3) contribute to the Global Atmospheric River Reconnaissance Program (GARRP). The deployments started in September 2025, and to date M3E has released 20 buoys, some of which were available in January 2026 when storm Harry affected the Mediterranean region. Harry 's synoptic conditions and extreme weather, including three‐day precipitation totals over 400 mm in southern Italy, are discussed. The European Centre for Medium‐Range Weather Forecasts Integrated Forecasting System was skilful in resolving Harry 's large‐scale circulation and the precipitation in southern Italy seven days ahead. There were forecast challenges in capturing the North African precipitation due to mesoscale low‐pressure systems. The benefit of the M3E buoys was shown using the Forecast Sensitivity to Observation Impact analysis, and an Observing System Experiment suggested sensitivity of the mesoscale features in storm Harry to the buoy observations in the Ionian Sea. These extra observations positively affected the extreme event forecasts and provide evidence for supporting future M3E deployments. In turn, this would help to sustain the GOS surface network, leading to socioeconomic benefits via improved weather forecasting of extreme weather systems, and contribute to the goals of GARRP.