I would leave it exactly as it is. First of all, Gustav and Gustaf are not identical. And unless Gustav turns into the type of killer hurricane that kills thousands and completely wipes out New Orleans again, the reference will be forgotten within a year. Would you hesitate before using names like Dennis, Emily, Rita or Wilma (all 2005 hurricanes), Ernesto (2006), or Dean (2007)? Nobody remembers those unless you're specifically talking about hurricanes.
And I know several women named Katrina, who were named that before the hurricane of that name, and haven't changed their names since.
It is what it is...
Cheers!
Al B.