Well in general Hispaniola can generally kill off systems due to it having the highest elvs. Cuba is just narrow and does have the ability of weakening a system greatly depending on if its strengthning or not coming to landfall..In general it could weaken it maybe 20-30mph or just destroy it...matters on how fast the system is moving at that time and also where it crosses and at what angle. If it crosses western cuba it can still weaken about what I posted above,,,,if it crosses central or eastern at a speed of 10mph or less then it could be alot greater.