This shadow is the easiest to see of Jupiter's Moons. Even a reasonable 60mm should do the job. I mention it because the time is so convenient and there will not be many more Jovial events before Jupiter gets very low.
Astronomy 2019 says shadow ingress at 21:21 and the Red Spot on the meridian at 20:00, would be a nice to observe and image. The cloud cover here will make that problematical.
Typical ..cloud cover here in Sydney.
I always look forward to the Red Spot coinciding with a shadow transit or transit...will be looking for a sucker hole between watching football.
Bigjoe .
22h 50m ..Jupiter-Moon GanymedeTransit End (III.Tr.E.; 5.4 mag) Altitude=10.1° Azimuth=249.4°.
PS: If youve got a 4 inch or larger scope and high power you'll ACTUALLY see its real disk and not just the spurious disk (a diffraction effect)of small apertures.
Hope that helps.
Bigjoe
October 10th looks interesting too, few weeks yet. Clouds and Jetstream look good for this Saturday evening but nothing happening with transits or Red Spot . Last night should have been interesting too but for the ubiquitous clouds.