The 17 February 2010 South Atlantic Downburst Storm

During the morning of 17 February 2010, the Canadian Sailing Vessel (SV) Concordia sank off the coast of Brazil, near Rio de Janeiro, most likely due to strong convective storm-generated winds. The SV Concordia was capsized in a downburst that occurred around 1500 UTC about 500 km off the coast. Graphical microburst potential guidance derived from a three-hour forecast of the Global Forecast System (GFS) model, valid at 1500 UTC, indicated a high risk of downbursts in the approximate location of the sinking of the Concordia. A conditionally unstable temperature lapse rate, large atmospheric precipitable water content, and the presence of mid-tropospheric dry air, as indicated by low relative humidity at the 500-mb level, contributed to strong downdraft instability that resulted in the downburst and hazardous winds on the ocean surface.

Figure 1. GFS model-derived graphical downburst potential product at 1500 UTC 17 February 2010.

A favorable downburst environment is illustrated in Figure 1, with the highest risk area outlined in red. The juxtaposition of a conditionally unstable temperature lapse rate (> 7K/km), large atmospheric precipitable water values near 50 mm (2 inches), and low mid-tropospheric (500 mb) relative humidity near the location of the sinking of the SV Concordia suggests that precipitation loading and mid-level dry air entrainment were major forcing mechanisms for strong convective winds. The presence of mid-tropospheric dry air fostered convective instability and the generation of negative buoyancy due to evaporational cooling as the drier air was entrained into the precipitation core of the convective storm. The combination of these forcing mechanisms would result in the acceleration of a downdraft to the ocean surface and the generation of a downburst that capsized the SV Concordia. For more information, please read:

http://www.cbc.ca/canada/story/2010/02/22/sinkingbrazil-shiptimeline.html