tx_chava,
Welcome to Flyertalk!
I assume the hotel you are looking at is the JW Marriott Ko Olina, which is a fabulous choice (although the info I am giving you applies to any Marriott upgrade on an award reservation).
Basically, when you reserve a room on an award, you are reserving a standard room..... garden view, mountain view, quality room, whatever they call it, it's a non-view room (especially at a beach resort). From there, if you want a pool view, or a partial ocean view, or an oceanfront view, that's a premium. Usually you can use points (5000 per night per level of upgrade.)
Some rooms, like an oceanfront at Ko Olina, are considered 4 levels up, therefore an upgrade to that room will be 20k Marriott points per night

or $120 (for those holding previous reservations, this level has recently gone up from 15k/$90 per night so be sure you are charged according to what level was in place when you reserved).
Understanding that you are Platinum and may be entitled to a better room, you may STILL find yourself with a not-so-perfect view IF when you check-in, the better views are sold out.
The best way to ensure the view you want is to actually reserve that view prior to arrival (like NOW!).
Then, when you arrive, your options are a bit more open. You can use points, pay the fee, or hope to be given the Platinum upgrade. Either way, you know there is an oceanfront (or whatever view you specified) room waiting for you.
Having stayed at the Ko Olina just a few weeks ago (and having Plat status as you do), I booked the upgraded room to what I thought was going to be a pure oceanfront room. I was a bit disappointed when we arrived and were given a room overlooking the pool, partial ocean view, and the industrial park down from the hotel with it's many smokestacks and concrete structures. (Oh did I mention it also overlooked the timeshare construction site, with several cranes atop a half-complete high rise?)
For this they were asking an additional $120 per night or 20k points?
Well, a chat with the Manager ensued (we had other problems as well......MANY bugs in the room upon arrival, and the room was a smoking with 2 double beds, both of which go against our Marriott preferences which BTW were guaranteed.)
He agreed that calling this an oceanfront room was really a stretch and was sorry to hear that we were displeased. To his credit, he rectified the situation more than adequately for us, and we will most definitely return to this location.
I do not mean to say that we did not like this hotel. To the contrary, it was beautiful and we loved it and would consider no other Oahu Marriott.
Just be forewarned that the upgrade might be disappointing, and prepare in advance to reserve the view you really want (and be ready to have to pay for it in points or cash).
And, if by chance the room you DO want is just a standard and you don't want to pay for an upgrade (yet no regular room availability shows), I would call the Marriott Platinum line, or better yet, call the hotels reservation desk directly, and see what kind of room they can offer you. September would seem to be relatively slow and I would be surprised if you couldn't secure a regular non-view room during that time.
Have a fantastic time....it's a great hotel.