Going to start out this reply by saying that I have been especially bullish on Irma's potential intensity for a couple of days now, and my confidence in this has only increased with each and every day. However, there are caveats. Subtle, but very possible changes in Irma's track, and/or degree of shear imparted by the upper low to her northwest, and/or potential for downstream effects from a (possible, but not yet NHC endorsed) development in the southern Gulf, etc. could have profound and as-of-yet unforeseen impacts on her future intensity, as well as track.
Given what is already known, plus considering the known unknowns, and unknown unknowns, my confidence for Irma's top wind speed during her lifetime breaks down along the following percentile basis (Please keep in mind, this is the "Lounge," and as such, I am taking wide liberty in sharing this, which is not, by any means, an official forecast. Please refer to the National Hurricane Center and its sister agencies for official information.
Opinion only. Top 1-min sustained wind speed attained by Irma at some point
High-end Cat 5 (175+ MPH) 35%
Cat 5 (160-170 MPH) 30%
Cat 4 (130-155 MPH) 25%
Cat 3 (Already attained) 10%
Put another way, it is my opinion (only) that Irma has almost a two-in-three chance of becoming a Cat 5 at some point before final landfall or dissipation at sea, and a 90% chance that Irma at least becomes a Cat 4.
I am rarely this bullish on a system. I was very bullish on Harvey, for example, but not nearly so much on any of the other TCs we had up until that point in the Atlantic basin this year.
Recon is finally getting in to Irma later today, which will help resolve some of the known unknowns, and maybe even some of the unknown unknowns. I will also be paying especially close attention to what happens with the Gulf trof, as well as (and they are of course all connected to greater or lesser degrees), the evolution of the Bermuda High. Again, recon flights will be very beneficial to my own opinions, as well as future model runs and official NHC forecasts.
Should Irma become both a large and very powerful hurricane (very plausible), locations prone to surge in her path may need to evacuate. Again, this is still highly speculative at this point, not an official forecast, and several days out.