Derecho Storm – 18 August 2022 - Corsica

Posted on 19th October 2022


A rare Derecho storm (a Mesoscale Convective System event) formed during the night from 17th to 18th August 2022 over the northern Balearic Islands and then rapidly moved towards the north east, hitting Corsica early in the morning.

In Corsica, at least five people died on land and 20 were injured, and 125 water rescues were also required. Winds up to 225 km/h (120 kts) were reported at Marignana with widespread gusts of 111 km/h (60 kts) (Sari-d'Orcino) to 206 km/h (110 kts) (L'Île-Rousse), including 158 km/h (85 kts) in the capital of Ajaccio.

Of note was the experience of boats moored in Girolata bay on the west coast north of Ajaccio, which is a beautiful and very popular bay in the season, being well protected from the prevailing NW breeze by a hooked headland. So popular that once the season starts anchoring is only possible further out in slightly more exposed water. The tucked in north bay is turned over to laid moorings which it appears from the photograph below are remarkably close together – rather like supermarket parking – but considerably more expensive. Which does not bode well in a blow. 


A week before the long range forecast was suggesting a weather system with strong breeze from the north west would track down the Med. and push through the Bonifacio straits between Corsica and Sardinia as usual and make it a bit uncomfortable around south east Corsica and north east Sardinia as it splayed out the other side towards Italy. Thus I moved from north Sardinia and went to Porto Vecchio on the east coast of Corsica with its big and deep sheltered anchorage around the port where it looked like it would be quite breezy for a couple of days, but well sheltered water. Similarly, I am sure, the boats packing Girolata (and Ajaccio) bays thought they were well protected. However the bay is wide open to the SW and West with high cliffs all around.

The change of forecast was late to be flagged as an Alert by MeteoFrance and the Authorities and landfall of this storm on Corsica, which tracked from SW to NE counter to expectations of weather that day, was early morning just as people were emerging from their bunks for another relaxing day. As you can see from the YouTube links attached here it arrived quickly and with stunning force.

What also confused me initially when viewing the videos was how so many boats could have dragged anchors into such a tight knot. Then I remembered the mooring field and realised they were, for the most part, relying on laid moorings and were far too close to their neighbours, and had no time to get out. The resulting carnage is a stiff wake up call, to a) how climate change is creating unusual conditions with greater frequency and which are more intense, b) the need for vigilance and trusting instincts, c) anchoring where you can lay enough scope and have room to swing, as well as tell others how much chain you have out and if they are too anchoring too close. 


Girolata bay, Corsica after 18 Aug. 2022 storm




For my part over on the other side in Porto Vecchio?
I got clobbered too but was lucky!

Expecting strong breeze of 30 – 35 kts I pushed on up into the large open protected anchorage right up the inlet, a natural harbour since Roman times and probably before that. Depth is 4 – 5m and shallower and the bottom is heavy black mud with sea grass. So on the 16th August I set up in 4m of water (draft 2m) and deployed 50 m of 10mm chain and my good old reliable 25kg Delta anchor. 

17th August wind blowing up the estuary from the east at 20 – 25 kts all day and into the night. Expectation was for a 180 degree switch in direction around 0900 hr on the 18th and then build up to stronger breeze again above 30 kts. At 0630 when I went on deck to check all was flat calm and quiet. I contemplated trying to drag the chain around so I would be set up for the change in direction but thought there was always a danger of making a mess and hooking up the keel as the water was so dark and murky I could not see the lie of the chain.

Returning to my bunk for a while, at around 0800 hrs all hell broke loose as the boat was hit by a sudden blast of howling wind and the boat leaning hard over.  Getting on deck straight away I started the engine and looked to see what was happening around me. By now there was blinding horizontal rain and wind that was in excess of 60 kts and the boat was facing west. It was soon also apparent I was dragging the anchor which surprised me. That was until I realised we had just run 100m from our start point and probably gathered 6 – 7 kts of boat speed sideways, before flipping the anchor out of the bottom as the tension suddenly came on from the opposite direction it was set in. With only two expensive yachts behind me, now far too close for comfort in the conditions, but safely clear, all I could do was drive the boat forwards under power and work to keep her straight into the wind, but actually not moving forwards at all. After 45 minutes of this the wind eased to just very windy, and half an hour later was to around 20 kts and a point at which I could safely try to get the chain and anchor up. What came up was a huge chunk of muddy seabed clogging the Delta flukes – so resetting itself was never on the cards. Quietly drifting off downwind now I managed to clear the mud off the anchor and moved further down the inlet to a sandy anchorage of known good holding and anchored again set up for another 48 hours of 25 kts.  Which by comparison was a pleasure…

Lesson? I was set up well, decks were clear and everything stowed properly, the location was good, I could have anchored in shallower water which amplifies your scope, but ultimately with a muddy and weedy seabed and a 180 shift I should have pulled up the anchor at first light and set again for the new wind direction just to be sure. Lesson learned!

 John Quigley, Co-founder and CEO YachtDataBank

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