I have to admit, I did find interesting Dr. Gray's factors for the August activity. To recap that section, he uses 12 factors for activity during August. Of those 12, only 5 were considered to be favorable for TC development.

September is a different story...7 total factors, 5 favorable. October was given a favorable outlook as well, with 3 out of 4 factors having an enhancing effect on TC activity.

So, it isn't out of the realm of possibility that September could have a very heavy concentration of activity.