I keep finding a good half inch of water under the driver's seat of my U.S. Rogue. Front floors and under the passenger front seat are dry.

We've had a good deal of rain here in the northeast all summer, but I'm not sure it's a rain issue (leaky door seal).

Is this a known issue? Any thoughts as to whether it may be A/C related or possibly from the windshield washer reservoir or sunroof drain? I sop it up with a bath towel, and a few days later another 1/2” or more in that area.

Thoughts?

It's probably a sunroof drain, that's an endemic issue on the gen2's. Open the roof and pour water into the outermost channel, that's the drainage. On level or downhill ground it should come out a few seconds later behind the front wheel. On an uphill it should come out behind the rear wheel. If you get nothing or only a slow drip, that drain is clogged. On Rogues it's almost always the fronts that clog, but fortunately they're easy to clear. Remove the wiper arms with a 14mm, remove the clips holding the cowl cover and take the cover off, remove the wiper motor assembly (three 10mm's) but don't disconnect it, just roll it back. Now you can access the drains tucked up in each corner of the cowl. You'll find a plastic diffuser nub molded into the drain fitting, grab it with a needlenose and rip it off. Those are what causes the clog. Usually they'll run clear as soon as you remove the diffuser, but poke a screwdriver up there just in case. Once the nub is removed they rarely clog anymore. This post has pics so you'll know what to look for:
post6844183.html?hilit=murano%20drain#p6844183

Thank you for the assistance! I value your input! You helped me out last summer regarding a ventilation fan motor issue

Just out of curiosity before I try to diagnose...
If the clog is in the cowl area in front of the windshield, how is the water getting to the area under my seat? The front floor is totally dry.

If an unclogged drain drains down below the car, what's the connection to the cowl drains?

The drains work by having channels that surround the roof pane and a drain hose at each corner. The front drain hoses travel down the A-pillars and exit into the cowl, the rears travel down the D-pillars and exit underneath the rear bumper cover. When water overflows the channels because of a blocked drain, it follows the same paths but outside the hoses. So water at the front flows down the back side of the A-pillar trim and the backside of the kick panel trim before running underneath the carpet. Unless there's enough to stain the headliner, it's pretty much invisible. Underneath the carpet there's about a 2" foam spacer front and back, so the only "low spot" on a Rogue to notice anything is directly underneath the seat. It's very insidious.

Since it sounds like you have enough water down there to be sloshing around, you'll probably need some help from this thread too:
after-the-great-flood-t628490.html

PS - One other thing specific to Rogues, overflowing front drains sometimes drip directly onto the SMJ's (the big gang connectors at each end of the dash) and the smaller electrical connectors around them. It's always a good idea to break those open and chase any water out with WD40. If there's any green on connector pins, treat them with Deoxit first and use dielectric grease afterward to assure that the corrosion never gets worse.

1st part of the job done. Next comes the cleanup of the carpet (and a little bit of staining on the headliner at the pivoting grab handle).

The left side front drain (red arrow) was clogged, and water was going forward, into the area with the hinged deflector plate. (yellow arrow). I broke off the round plug at the bottom of the drain(s). I needed to stick a screwdriver in the driver's side drain to loosen the gunk within, and then the water came flowing out like from a garden hose.

I've some tips for anyone else doing this, and a few more questions.

Tips: the covers over the windshield wiper nuts are push-ons. Put a thin, slotted, screwdriver under an edge and just pry up slowly. They'll pop right off.
The wiper arms are just pressed down upon a splined spindle. To remove them, just pull up. Mine were on extremely tight. I had to give them a couple of light taps on the side of the rounded part of the wiper arm to break them free. Then they just pull straight up with NO twisting.
There are 7 cowl clips that need to be removed. There are also 2 non-removable clips, one at each end. I took a needle nose pliers and squeezed the clip ends together to allow the cowl to be removed.
The cowl's front is attached to the channel that runs along the bottom of the windshield. I had to use some firm force to get one end to detach. Then the rest of the cowl pulled away rather easily.
I didn't remove the cowl entirely. I just flipped it out of the way, as the washer fluid hose is still attached to the cowl.

Questions: When reinstalling the cowl, it kind of snaps in place into the windshield groove, but it doesn't impress me that's it's rigidly affixed. I don't foresee it moving as it has the 7 (total of 9) clips in the engine bay. Should I have used some type of adhesive (silicone, urethane, etc.) To affix it better to the windshield groove?

Is there a drain up top at the front of the roof for water that comes in at the front? Or does it need to flow "back" towards the front drains (red arrow).

If it had been a rear drain issue, are they accessible from up top as it seems the glass panel doesn't go far enough back to even see the rear drain?

The cowl cover will settle into that groove and won't go anywhere, no worries about that. No adhesive needed. The frontmost channel which intersects with the drain is where the water goes, so it runs to either side and out the corners. It's aligned under the front edge of the pane, so water won't come down anyplace rearward from it unless the roof is left open. In back there's a "traveling trough" that slides back and forth with the pane and directs water into the side channels, that's similarly aligned with the rear edge of the pane. One of the rear drains is a little more difficult. The driver's side can be reached easily by removing the jack. The passenger's side requires loosening (but not removing) the lower cargo area trim. Getting at either one from the outside would require loosening the rear bumper cover, which is a PITA. Instead, stick a thin screwdriver all the way through the fitting from inside and push hard to break off one side of the diffuser nub. That's usually sufficient to prevent any recurrences.

Pro tip, instead of tapping on the wiper arms to loosen them (which can be risky to the windshield, depending on what you're tapping with), just grab the arm to the left (looking from the front) of the flex joint and yank it hard a few times up and down. Pop goes the weasel, no tool needed.