I recently looked over some hurricane data from 1851 until this year. I got curious: on what day of the year is there the most hurricane activity? Answer: September 10. There have been 96 active hurricanes on that day since 1851.
To create this graph, I downloaded a data set from the NOAA Historical Hurricane Tracks page: http://maps.csc.noaa.gov/hurricanes/download.jsp. I downloaded the dataset for both basins. It comes in the form of an ESRI ARCMap dhape file, but there is a dBase dbf file that can be imported into Micosoft Access (if you try this, you may run into some trouble unless you rename the DBF file to have a normal eight character file name).
I used Microsoft Excel to query the data from the Access database I had created and create the graph. I had to be careful in my query not to double count hurricanes that had more than one weather advisory on the same date.