None of the floods that happened in the last couple of years even came close to Harmony. I did a good amount of research on that.
The only areas I'd be worried about are the very, very back of Benders and portions of Woodson's reserve. Also, the back of the Falls at Imperial Oaks on the North side of 99 gets pretty close to the river which is also what swayed us away from that particular community among other reasons.
SE Montgomery County just East of 45 didn't really develop since there wasn't great access into it before. With 99 open, many companies recently moving to the Woodlands/Conroe area, and the Woodlands close to build out, it's taking off. Will some areas flood eventually, sure, but that's pretty much the norm in many areas across Houston, even Kingwood. I remember 1994 with water all the way to Kingwood Dr on West Lake Houston Pkwy.
Best of luck OP. I'm sure you'll be happy no matter where end up.