2005 was a record year for hurricane devastation in the United States (San Luis Obispo Tribune, November 30, 2005). Of the 26 tropical storms and hurricanes in the season, four hurricanes hit the mainland: Dennis, Katrina, Rita, and Wilma. The United States' insured catastrophic losses since 1989 (approximate values read from a graph that appeared in the San Luis Obispo Tribune, November 30, 2005) are as follows:
a. Construct a time series plot that shows the insured catastrophic loss over time.
b. What do you think causes the peaks in the graph?