Tropical Depression 15’s Europe Threat

The animation shown here is one of 50 forecasts from Saturday 17th run by the ECMWF every 12 hours to help us understand uncertainty in weather forecasts. The left side is central pressure, the right side is peak wind gusts every 6 hours.

This particular forecast is one of many outcomes, but it shows the remnants of Tropical Storm Nigel becoming reinvigorated by the jet-stream, transitioning from a tropical to an extra-tropical system and approaching Europe as a strong extratropical storm; a windstorm whose strength would likely be weaker if it wasn’t for the area of warm air that Nigel is forecast to bring up from the tropics. This type of interaction can only typically happen in a sweet-spot towards the end of summer where tropical and extra-tropical storm seasons overlap and warm tropical air can be brought north by tropical systems to meet the jet-stream.

Since the era of catastrophe models from the early 1990s onward we’re probably yet to be really tested by a noteworthy strong, loss-causing ‘ex-tropical’ system in the UK and near-continent. We’ve had recent shots across the bows before from the likes of ex-Hurricane Lili in 1996 and ex-Hurricane Ophelia in 2017 – and deeper into history, ex-Hurricane Debbie in 1961 killed 18 people in Ireland, so there are precedents for this type of system. These are not “black swan” events: we have historical precedents.