First off, the starting position. It seems more fair to assume a height of 1000 meters. Using this gets us 112.9 km horizon distance.
Moving on. Clouds are 9144 meters tall average. Volume of a cylinder with a 112900 m radius and a 9144 m height nets us 3.66e14 m^3. Density of a cloud is 0.0005 kg/m^3, netting us a weight of 1.83e11 kg. Moving on.
This calc says the storm started at 0:03 and was finished being created at 0:09 and goes on to say this is 5 seconds. This is 6 seconds. Moving on again.
The storm would have traveled its radius in a big circle, so we can use the distance of the radius as our distance traveled in that time, netting us 18816.67 m/s (Mach 54.86, High Hypersonic+). We can get KE now of the storm's diffusal.
KE = 0.5m * v^2 = 3.240 x 10^19 Joules, Island level. However, as this is a low-end, we can do a high-end at 2000 meters.
New radius is 159.7 km, making new volume 7.33e14 m^3. New mass is 3.665e11 kg. New speed is 26616.67 m/s (Mach 77.70, High Hypersonic+). New KE is 1.298 x 10^20 Joules, Island level. There.
Al'Akir Creates a Storm (Low-End): 7.74 Gigatons, Island level
Al'Akir Creates a Storm (High-End): 31.02 Gigatons, Island level
Much more consistent. No hard feelings to Myriad (the original calc'er), a lot of this wasn't even remotely his fault. Cheers bois.