According to the NOAA, October 2013 was the 37th coldest since 1895. 1963 was the warmest.
Is it unusual for there to be a cold October since … say … 1998? Nope.
They are spread all the way from 4th warmest in 2007 to the 4th coldest in 2009.
| year | Oct | Oct Rank (1 = Coldest / 119 = Warmest) |
| 2007 | 56.78 | 116 |
| 2003 | 56.57 | 113 |
| 2010 | 56.21 | 106 |
| 2004 | 55.55 | 101 |
| 2005 | 55.48 | 99 |
| 1998 | 55.24 | 91 |
| 2011 | 55.18 | 89 |
| 2000 | 55.17 | 87 |
| 1999 | 54.59 | 70 |
| 2001 | 54.39 | 64 |
| 2008 | 53.95 | 49 |
| 2012 | 53.91 | 45 |
| 2013 | 53.58 | 37 |
| 2006 | 52.69 | 24 |
| 2002 | 51.85 | 14 |
| 2009 | 50.61 | 4 |
sunshine hours 
Unlike the summer, October has not seen any warming in recent decades (according to my research).