I agree with Ohio, attend the meeting. You may be able to ask them to put you in contact with whoever does it for your new area. If they can't, I would suggest you contact your incoming HS GC now, because they probably know who it is also. I understand you may not know which HS, but traditionally, these people cover all of the HS's for a particular county, and from a realtor perspective, I know the majority of my clients with kids in school, always placed the school as the top priority, than the home wish list.
I wouldn't be too concern over this, in the military it is quite common, unfortunately, that kids move during their rising sr yr due to their parents careers. (This is one of the reasons why the Presidential nom for SAs exist). Most military families move in July, so these kids will be in the same boat as your child.
The one thing I would do is get their transcripts sealed and HAND CARRY their records. During the summer some schools will shut down for a few weeks and only the front office is there. If your outgoing or incoming hs does this, it could cause a delay. EX: outgoing closes from July 1st to 15th, incoming closed from 15 July to 1 Aug. That means you can't register for classes and move forward. Hand carry them, and arrive July 1st to the new school, and you are good to go.
Again, contact the incoming HS or the county school administrative offices to see if they will allow this. Traditionally, it is not a school by school choice, it is a county wide acceptance. Best to double up your bet by asking if you could have their email address (county) and shoot them this email requesting verification in writing. Print it up and hand carry that too.
HS's really don't like records to be hand carried because you can mess with them, so that is why it is important to get it in writing. We did this, and they placed a caveat... they would register them for classes, but if the HS faxed them different records, it would change.
One thing to think about, is be prepared that their gpa may change. Our kids outgoing hs had a 7 pt scale with a 5.0 weight for AP, incoming was 10 pt with a 4.5 wt. This is also why many people, including me place little emphasis when posters state I have X wgpa. It is because we know selection boards will re-weight to their system. This was an issue for our DD, because they had to go back and look at the last hs's system, and re-weight every class because of not only the scale, but also that school had Std., honors and APs, whereas they only had Std or AP. They changed it 3 times on her, upping it each time because they also requested the school class selection brochure and determined that at their last school, you couldn't take AP unless you took Honors 1st, in other words if you wanted to take AP Bio, you took Honors Bio, and than AP. It hindered her at the new school because she never had that option since in 10th it would have been std or AP, same with Chem. They were really terrific and worked with her sorting through what was std to them and what honors would have been AP comparable without the tests.
It was a long process and if I recall correctly it was Nov before they had it all sorted out. Not saying this will happen to you, and I hope it doesn't because it means constantly sending new transcripts, but I am saying be prepared, and the best way to do that is to start investigating now.
Our final problem was PE. Believe it or not it was an issue. Old school required only 1 yr of PE, new school required 3 to graduate. She was probably the only sr with 2 PE's and the funkiest schedule...the rest of her classes were AICE/AP.
OH and also many, most states will require a yr of history that is their state. DS1 moved to NC and had to take that as a jr with freshman because we came from VA and he did not have their box checked. DD had to also because we moved from NC to VA and she didn't have VA history. Stupid, I know, but that is how it worked for us.
Hope all of this helps to give you a better picture on how things may play out for schools when you move.
Good luck.