Took a look at the past 60 years (1942 - 2001) and compiled the average number of storms that have occurred on or after a certain date. Might be useful to check back on this as the season progresses.
07/30 8.65 (range 17 to 3)
08/10 7.98 (17 to 3)
08/20 7.17 (14 to 3)
08/30 6.07 (12 to 2)
09/10 4.58 (11 to 2)
09/20 3.45 (10 to 0)
09/30 2.38 (7 to 0)