A rapidly developing extratropical cyclone named Tini brought strong winds to Ireland and the United Kingdom on 12 February 2014. A mesoscale-model simulation is used to analyze the development of the strong winds through the terms in the horizontal momentum equation. The maximum of near-surface wind speed equatorward of the cyclone was composed of two different airstreams that underwent different paths to acceleration. First, horizontally moving air in the cold conveyor belt was accelerated by the along-flow pressure gradient force but was decelerated by friction. Second, descending air accelerated into the eastern end of the maximum of near-surface wind speed and was associated, in part, with a sting jet, caused by the increasing along-flow horizontal pressure gradient force at lower levels. When this descending air entered the boundary layer, it too was decelerated by surface friction. Surface fluxes of heat and moisture were necessary to destabilize and deepen the boundary layer, allowing mixing of the strongest winds from the free troposphere down to the surface. A simulation with the surface fluxes turned off during cyclogenesis showed a more stable boundary layer around the bent-back front, which inhibited the strongest winds from reaching the surface. The descent of the sting-jet air was associated with a maximum in quasigeostrophic omega, which consisted of both synoptic-scale and mesoscale descent, the latter associated with frontolysis occurring at the end of the bent-back front. Thus, the near-surface wind maximum was created by the synoptic-scale and mesoscale dynamics, whereas localized moist processes were negligible.

To understand near-surface strong winds in extratropical cyclones, a simulation of a dry, idealised baroclinic wave is presented. The forces that accelerate the winds are analysed using the terms in the horizontal momentum equation. Two regions of strong near-surface winds developed within the simulation: one to the east of the low centre and the other to the southwest. The flow to the east, resembling the cold conveyor belt, accelerated as it passed through the strong pressure gradient associated with the warm-frontal zone. This acceleration was reduced by friction near the surface. The winds to the southwest were characterised by three airstreams. One airstream consisted of air parcels that started north of the warm front near the surface, accelerated north of the warm front, encircled the low and continued to accelerate to the southwest of the low. The increases in wind speed in this airstream (also part of the cold conveyor belt) resulted from the along-flow pressure gradient force being greater than friction. The second airstream consisted of air parcels that descended west of the cold front and maintained their speed during descent until they were slowed either by friction in the boundary layer, or as they moved southward against the local pressure gradient. Between these two airstreams, a third airstream was characterised by air parcels that accelerated during descent from the mid to lower troposphere whilst moving around the bent-back front. This airstream bears some resemblance to the sting jet and was accelerated by the pressure gradient force on descent until it encountered increased friction or moved against the local pressure gradient.