[paul cotter (OP)]

We have just had the first named storm of the winter storm season here in the British Isles. Why do these storms occur in winter with such vigour when there is less energy available in the atmosphere, compared to summer time? The American Atlantic hurricane season runs from high summer to the end of autumn(fall) when the seas are warm and atmospheric energy is high. Any thoughts?

[alancalverd]

Weather systems depend on temperature and humidity difference rather than temperature alone. The Atlantic, and particularly the Gulf Stream, being closer to the equator, cools slower than the Arctic ocean as winter approaches, so the temperature and hence pressure difference between tropical and arctic air increases. This causes more vigorous convection where the air masses meet.

Convection combined with the Coriolis-induced rotation of the resulting confluence can result in a deepening central depression so instead of dissipating as the cyclone moves east and north, the core can intensify.   Landfall is partly dictated by wiggles in the jet stream (to use a technical term), which can also increase the speed of rotation of the cyclonic core.