What seemed obvious is turning out to be the case. Crew attempted to land with severe thunderstorm on runway. Became unstable, touched down long and fast, hydroplaned off the runway. Pretty much a typical scenario.
http://www.tsb.gc.ca/en/reports/air/2005/a05h0002/a05h0002_update_20051116.asp
At about the time that AF358 landed, a sharp boundary of rain associated with the thunderstorm moved approximately north to south over Runway 24L, accompanied by wind gusts and a change in surface wind strength and direction. Severe lightning and lightning strikes were also reported during this period. At 1604, the conditions observed at the weather site to the south of Runway 24L were winds 340 degrees true at 24 knots with gusts to 33 knots, severe thunderstorm activity over the airfield with a visibility of 1 sm in heavy rain, and a reported ceiling of 4500 feet agl.
Digital Flight Data Recorder Information
During the final approach phase, the aircraft's FMS showed the wind coming from 300 degrees true at between 15 and 20 knots, with an approximate 8-knot headwind component. The crew changed the aircraft's automatic brake setting from the "low" to the "medium" position in view of the expected reduced runway friction conditions for the landing. The aircraft was aligned with the localizer and glide path. The approach speed was 140 knots, appropriate for the computed aircraft weight of 185 tonnes for the landing. The autopilot and auto-thrust systems were engaged for the approach. Both were disconnected at about 350 feet above ground, from which point the crew continued with the approach visually and landed in accordance with the airline's standard operating procedures (SOPs). The aircraft then went slightly above the glide path and arrived over the runway threshold at an estimated height of 100 feet; the normal height at that point is 50 feet. At that time, the indicated airspeed increased from 139 to 154 knots. During the flare, the aircraft entered a heavy shower area, and the crew's forward visibility was significantly reduced as they entered the downpour. The digital flight data recorder (DFDR) recorded wind veered to 330 degrees true, causing a tailwind component of approximately 5 knots. The runway became contaminated with at least ¼ inch of standing water.
The aircraft touched down approximately 4000 feet down the 9000-foot runway. The spoilers deployed automatically after touchdown and the DFDR recorded that the crew applied maximum pressure to the aircraft's brake pedals. The pressure remained constant until the aircraft departed the end of the runway surface.
......The aircraft departed the end of the runway at a ground speed of 79 knots. It came to rest 1090 feet beyond the departure end of the runway. The DFDR data show that the aircraft landed with 7500 kg of fuel; 4500 kg of trip fuel was required to fly to Ottawa.