Southern Swell in the Indian Ocean

On the evening of May 12, 2007, a series of very high waves broke over Reunion Island, in the Indian Ocean, a phenomenon that was repeated during May 14 to 15 night. The waves did numerous damages, on Reunion and neighbouring islands; several people disappeared. Those waves reached on May 12 maximum heights of 11.3 m (6.4 m of significant wave height), and 8 m on May 14 to 15 night, as measured by wave gauges.
An alert was emitted by Météo France on Friday, 11, morning, and re-evaluated on Saturday, 12, with an higher swell.

This phenomenon, called "southern swell" is due to an heavy storm around 40°S (the famous 'roaring forties'), South of Africa. The storm engendered swell, which propagated in the Indian Ocean at about 1000 km/day, going over the Reunion, in a region where low winds do not disrupt the swell.
Lasting long enough, and with a rather large extension, it has been observed by multiple altimeter tracks. The 1st swell caused waves higher than 15 m (significant wave heights). Jason-1 significant wave heights are thus around 10 m South of the island on May 12.
Altimetric data from Jason-1 and Envisat helped better forecasting of this phenomenon by being assimilated in Météo France sea state forecast models.

Jason-1 Significant wave heights along the track on May 12. South of Reunion island, the satellite overflew an area of high waves. This figure is made with data available 2 h after the measurement (OSDR), which are the one being assimilated in real-time sea state forecast models.




Significant wave height animation between May 1st and 16th in the Indian Ocean (data merging several altimeter measurements). We can see the arrival near Reunion Island of a higher wave area between May, 12 and May, 13.





Significant wave height animation between May 1st and 25th in the whole Indian Ocean (data merging several altimeter measurements). The waves propagate in the whole ocean, reaching Indonesian coasts.