I agree with twizted sizter - how can these systems possibly get close together? Erin is about a day from landfall and will quickly break up over the higher elevations. Dean is still over a week from Erin's position - in fact, NHC places Dean's 5-day position near Jamaica.

About the only way that Erin could affect dean is if it weakens the high pressure system developing over the central US that is going to cut Dean off from an east coast hit and help force it into the gulf. But that high pressure is dropping down from Canada, and the 12Z GFS shows Erin's remnants no where close to the high pressure system, so it is unlikely affect it much at all.

Further, tropical systems in close proximity disrupt each other, not strengthen each other, so your premise is false.

As for satellite imagery sources: SSD, GHCC, NRL, etc. Take your pick. Each is better at different things. SSD is the easiest to use and has multiple color overlays enabling better understanding of the system. GHCC has longer term and fully customizable animations. NRL has microwave imagery and multiple satellites. There are other sources too, but these three tend to be the most useful.