I don't know if this is the best way but import the image as a fade filter and show that. The only problem with it really is that all fade filters immediately hides all tooltips.
Anyway here is a tutorial on how to import and use fade filters. Link.
Cinematic - Fade out and back in over 111111.00 seconds using texture war3mapImported\fade.BLP and color (100.00%, 100.00%, 100.00%) with 100.00% transparency