System taking up 53GB

If I understand correctly, these are all considered "purgeable" space, which means that the OS may release them if the need arises.

As it turns out, for many people it appears that the system tends to hold on to these purgeable items and not release the space in some cases.

You can select your drive and do a Get Info in the Finder and see how much purgeable space there is.

Here is what it says in mine:

If you see a lot of purgeable space, you can try running the tmutil command again.

Just to add, the size of the "System" doesn't actually reflect the size of the operating system which is actually somewhere between 9-15GBs. In "About This Mac" > Storage mine shows…

It isn't.

It's very misleading and leads to no end of confusion and worry.

One common reason for this is Time Machine local snapshots.

I suggest you first let Time Machine do its backup.

You can trim local snapshots with the following command in Terminal:

sudo tmutil thinlocalsnapshots / 10000000000 4

Enter your password as requested (nothing appears onscreen while you type the password, that's normal), and press enter.

Let the program do its thing.

(The forward slash represents your system disk; the large number is roughly 10G and is meant to indicate what one is trying to reclaim, you can vary this; the number 4 is the highest value for "urgency").

In the end, it may show a few lines similar to this:

Thinned local snapshots:

2018-03-07-125922

You can try as well to re-index the storage on your Mac. Try going to System Preferences>Spotlight>Privacy, then you can select the ➕ sign at the bottom left corner of the window and add your Macintosh HD hard disk. (if you cannot see Macintosh HD there you can go on Finder>Preferences>Sidebar and select from the Devices menu Hard disks to be ➕ instead of ➖). After you ➕ add the Macintosh HD there you will remove ➖ it right away and after a while you should notice your storage re-calculating and at some point you might see some more free storage on the Mac.