You all may remember me as the meteorologist who worked up the case study on Air France 447 several years ago. I took a look at the data and as far as I can determine, the last ADS-B position was at N6.80 E103.52, 2014-03-07 17:21, with the plane flying at FL350 and with a TAS of 474 kt.
Unfortunately with it being night, we don't have the best satellite imagery to work with, but the 10.8 micron infrared is shown below, with the flight track superimposed. Looks like mostly clear skies with thin cirrus debris at FL400-500. The animation showed weakening of this cloud field. So it's very unlikely that weather was a factor. Flight level winds would have been roughly 010/15, and with only marginal instability it looks like it would have been a smooth ride.
I would plot out the whole intended route, but I don't have the information and I don't have good charts of the RNAV structure over Vietnam. However the weather across Vietnam and north to Hong Kong looked VFR all the way.
Looking at other flights crossing between Malaysia and Vietnam I saw no interruption of their ADS-B data. Unless there was a problem with the transponder or a FIR handoff it appears the plane may have actually gone down at this spot. If worse comes to worse, that area is on the continental shelf and in only 150 ft of water and it doesn't get much deeper, so if the plane was lost and the CVR/FDR is down there, it should be nothing like the AF447 search.