The Bahamas is currently getting battered by Hurricane Joaquin, a Category 4 hurricane with winds gusting up to 140 kt (260 kph) and a storm surge of 6-12 feet (2-4 metres). With huge variation between the output of the various computer models, forecasting its movement has been remarkably difficult up to now, however it is becoming increasingly clearer that Joaquin will not hit the US east coast directly but will remain out to sea. From there its remnants look like heading straight for Ireland next week, but it will be a depression, not a hurricane, at that stage. How strong of a depression? Well it’s still hard to tell.
Hurricanes feed off huge amounts of latent energy released when warm humid air condenses to form towering clusters of thunderstorms. For these beasts to form and sustain themselves they require several conditions to be met. Sea-surface temperatures (SSTs) need to be at least 26.5 °C and vertical windshear must be small so that upper winds don’t tear the structure apart.
Joaquin has been gorging on SST approaching 30 °C, and this has made it the strongest hurricane of the year. Steering winds in the upper atmosphere are very light, meaning the storm has been moving at a snail’s pace and the models have been having a hard time of it. This means that the Bahamas are being pounded for hours on end and only after it starts to move off to the northeast later tonight will they receive any respite. Let’s hope the people have weathered the storm safely.
As it moves northwards over the next few days it will encounter both cooler seas and increased windshear as it gets clotheslined by the westerly jet stream. It will lose some tropical characteristics from around Monday as it heads towards Ireland during the following few days. Exactly how close it gets will be interesting to see, but the latest ECMWF model output has it as a 977 hPa depression just off our southwest by midnight Thursday.
Interestingly, this model has it still latching onto some tropical characteristics as it approaches Ireland, a bit like Gordon back in 2006. Remember him? He soaked the Ryder Cup at the K Club! Debbie in 1961 was another one that is believed to have still been tropical as it hit Ireland, however her very fast northward movement at around 80 kph made the winds worse than the gradient winds had she been moving slower.
History aside, I am looking forward to watching how the models handle Joaquin over the next week and how the storm itself reacts to its everchanging environment before reaching this part of the world.