Let's go in-depth a bit on the wind speeds associated with a hurricane. This explanation stands for any storm, not just Irma.
Hurricanes are usually massive, therefore they are divided into four quadrants. Interestingly enough, those quadrants actually have different wind speeds making some sections of the storm more dangerous than others. The most dangerous quadrant of a hurricane is the right front. The question is why? The answer is actually kind of simple. However fast a storm is moving in X direction is factored into the overall wind speed within the storm.
Hurricanes get their strong winds because of the massive pressure differences between the eye and the outer most bands of the storm. So we factor those wind speeds and the speed at which the storm is moving and you get an overall net speed. Example: A hurricane with 100 mph winds, that's moving 15 mph, will have a net wind speed of 115 mph in the right front quadrant.
Now, why the right front quadrant as opposed to any other quadrant? Well storms move in a counterclockwise direction, which essentially means in the right front quadrant you have the wind from the storm and the wind of the motion of the storm moving in the same direction.