When a hurricane weakens over colder waters or after landfall its warm and humid air is absorbed into the circulation of a travelling Atlantic temperate-latitude depression. It may provide sufficient added energy to cause a dramatic intensificiation of that depression, and this is undoubtedly the cause of some (but by no means all) of the severe September gales that have swept northwest Europe over the years. This is why weather forecasters sometimes refer to "ex-hurricane A" or "the remnants of hurricane B".