On 2 September 2013, an Airbus A330-200 crossing the ITCZ at FL400 at night encountered sudden severe turbulence unanticipated by the crew resulting in serious injuries to a few cabin crew / passengers and minor injuries to twelve others. An en route diversion to Fortaleza was made. The Investigation found that the origin of the turbulence was severe convective weather and failure to detect it in an area where it had been forecasted indicated that it was probably associated with sub-optimal use of the on-board weather radar with the severity of the encounter possibly aggravated by inappropriate contrary control inputs.