Storm Austen from the Atlantic to the North Sea: what buoys and satellites measured

• 9.5 mSentinel-6, mid-Atlantic
• 8.8 mSWOT, a few hours earlier

On Thursday afternoon Austen is still in the middle of the Atlantic. No buoy floats out there, but satellites pass over. At 5:09pm, Sentinel-6 measures a significant wave height of 9.5 m near 47°N 15°W, more than 700 km off the French coast. A few hours earlier, SWOT had already recorded 8.8 m in the same area.

Significant wave height is the average of the highest third of the waves. It is what buoys and satellites report and what The Buoy shows. The biggest single waves are roughly twice as high.

• 19.4 mhighest wave at Pierres Noires →
• 13.2 mJason-3 off Ushant
• 158 km/hgust on Ushant

The low comes in from the west and passes off Cornwall: pressure drops to 975 hPa on the Isles of Scilly around midnight. At 11:51pm, the Jason-3 satellite flies over the Iroise Sea and measures 13.2 m about 100 km west of Ushant, the highest satellite reading of the whole storm.

An hour later, at 1am UK time, the Pierres Noires buoy records a 19.4 m wave. The significant wave height peaks at 11.7 m around 2:30am and stays above 9 m until morning. On the coast, gusts reach 158 km/h on Ushant, 152 km/h at Pointe du Raz and 150 km/h on Groix.

• 18.1 mhighest wave at Belle-Île →
• 13.4 mhighest wave at Anglet →
• 10.6 mHY-2B near Belle-Île

The swell then runs south. At Belle-Île, the buoy measures 10.2 m with an 18.1 m wave around 8:30am. The Chinese satellite HY-2B passes nearby at 8:02am and reads 10.6 m, about 50 km to the west. Offshore, Météo-France's Gascogne buoy reaches 9.3 m at noon.

Along the Aquitaine and Basque coasts, single waves top 12 m: 12.2 m at Cap Ferret, 13.4 m at Anglet, 12.8 m at the Bilbao-Vizcaya buoy late in the day. In the Basque Country the measured swell beat the forecast: at Bilbao, the energy per wave at the peak was about 40% above what the ECMWF model predicted.

• 976 hPalow off Cap de la Hague
• 148 km/hgust at Fécamp
• 5.3 mswell in Poole Bay →

Meanwhile the low tracks up the Channel. It passes closest to Cap de la Hague around 6am (976 hPa), then Le Touquet at 11:30am and Bergues, near Dunkirk, around 12:40pm. Behind it the wind stays violent: 148 km/h at Fécamp mid-morning. On the English side, the swell reaches 5.3 m in Poole Bay and 4.3 m at Hastings.

• 5.3 mswell at the J6 platform →
• 5.2 mswell at Borssele →
• 1.6 mat most in Denmark

Austen leaves through the North Sea overnight into Saturday. The north-westerly behind the low raises a rough sea along the Belgian and Dutch coasts: 5.2 m at Borssele around 3:40am, and 5.3 m at the J6 platform around 6am, slightly above the 4.7 m the German model expected.

And Denmark? It was on the forecast track but barely felt it: 1.6 m at most on its west coast buoys. The storm ran out of steam before getting there. That same evening, another storm, Boelo, reached Scotland.