Casting a spell while an autoattack is in flight WILL make it an overload charge.

You can cast abilities and items while flying with your ult, even targeted ones!

Jump>Overload>Remnant>Overload>Vortex>Overload>Remnant>Overload>Jump>Overload, easy!

Make sure a gank will pay off before you go rotating. Storm is entirely a snowball hero, so ganks not paying off is extremely costly.