Attribution of observed extreme marine wind speeds and associated hazards to midlatitude cyclone conveyor belt jets near the British Isles

Extreme wind speeds, gusts, and wind wave heights associated with midlatitude cyclones pose a hazard to shipping lanes and offshore infrastructure operating in the North Atlantic Ocean seas surrounding the British Isles. Several studies have assessed the variability of wind and waves in this region using reanalyses, but few have used surface observations of extreme wind speeds and wave heights. Here, we use a network of marine surface stations to derive the 2012-2020 climatology of daily maximum wind speed events. An algorithm is used to attribute the extreme wind events, characterized as exceeding the 20 and 25 m.s(-1) thresholds, to the cyclone warm conveyor belt (WCB), and early (CCBa) and returning (CCBb) cold conveyor belt jets; cyclones are matched with up to 90% of extreme wind events. The CCBb is most frequently associated with the strong wind speeds, accounting for 46 and 59% of the events exceeding the two thresholds, respectively. The CCBb also leads to the largest number of compound wind and wave hazard events (37 out of 87). Although the WCB is associated with the second largest number of extreme wind events, the CCBa accounts for the second largest number of compound extreme wind and wave events (24). The ERA5 reanalysis underestimates the observed extreme wind speeds, and associated gusts and wind-wave heights, during extreme wind events for all the conveyor belt jets. The wind speeds and associated gusts are most underestimated, by median values of 4.5 and 5.5 m.s(-1), respectively, and similar percentage error (asymptotic to 25%), when associated with the CCBb; however, the wind-wave heights are most underestimated, by a median of 3.4 m, when associated with the CCBa. Hence, while the marine CCBb jet, found in mature cyclones, is both most hazardous and underestimated in the ERA5 near the British Isles, the CCBa jet can be nearly as hazardous when considering compound wind-wave events.