It's possible for storms to interact with each other, sometimes they cause shear (strong winds from one direction) that blow apart a storm or hinder it's progress. Sometimes a storm can do a fujiwara sort of dance of sorts.

Some links to read:

http://en.wikipedia.org/wiki/Fujiwhara_effect

http://www.helium.com/items/959858-twin-hurricanes-the-fujiwara-effect-explained

Also, you can have a set up like the Perfect Storm that was written about in the book made into a movie.

http://en.wikipedia.org/wiki/1991_Atlantic_hurricane_season#Hurricane_Grace

In reality storms often interact in different ways. A lot depends on timing, how fast Hanna moves out and there has been talk that Ike might be driving/pushing Hanna a drop.

Hope this helps.