Sexual assaults (and other serious violent crime) are more common in the summer months...
http://www.bjs.gov/content/pub/pdf/spcvt.pdf
For violent victimizations, seasonal patterns also vary
depending on the type of crime. Rape and sexual assault
rates and aggravated assault rates are higher in the summer
than in most other seasons. In comparison, simple assault
rates are higher in the fall than in other seasons, and robbery
victimization rates show no seasonal patterns. Intimate
partner violence exhibits regular seasonal fluctuations with
rates highest during the summer and lowest during the
winter. Rates of violence involving weapons and violence
resulting in serious injury are higher in the summer than in
the winter and spring seasons; however, the fall rates are not
significantly different from the summer rates.