We did the Baltic as soon as school was out a few years ago...June 2 or so....the weather could not have been more perfect. That is, however, in contrast to the prior year when we tried to cruise the Baltic, but our ship was damaged in Amsterdam's canal on the way out, so all canceled. The year of the canceled cruise, the weather was definitely cooler and damper. Celebrity totally avoided Amsterdam the next year, but we had already spent three days there on using our crippled ship as a hotel so that was OK with us.
I think that the port side was good for sailing from Dover on through the Baltic and back. We had a suite on the port side of the Constellation for our successful cruise with a large balcony, and we loved it.
Somewhere I have lots of information on our Baltic cruise...private guides, etc. If you are interested, I will see if I can find it.