Cumulonimbus cloud that formed during a localized thunderstorm in Sicily as explained in detail here and moved over towards the Eastern side of Malta due to strong upper level winds (which are normal for that time of year). If it was not for the relatively strong upper level wind at 500mb shown in the 3rd thumbnail, the cloud would have long dissipated before reaching the Islands. Otherwise the weather sounding indicated a strong capping (Convective Inhibition – CIN) at the lower levels which would not have been possible to be break locally. The top part of the cloud is actually overshooting due to momentum from rapid ascent hence continuing above the end level of free convection as indicated in this weather sounding (2nd thumbnail). The mamma of this cloud is due to returning descending air which as indicated in the 1st thumbnail, the process takes over also on the overshooting top. The final thumbnail shows a stray shower from mid-level thunderstorm.