As we add capacity to the atmosphere to retain heat via the emission of greenhouse gases , we are invariably raising the temperature of the oceans. Due to the enormous heat capacity of water, it can absorb a lot of energy before a temperature increase occurs. Hence, we are not raising the global mean tempearture of the oceans (yet) but we are producing locally warmer water - which may in fact serve to reinforce the periodic El Nino effect.
Hurricane strength is directly proportional to the temperature of the water and the amount of time spent over warmer water. In general, Hurricanes require a surface temperature of the ocean of at least 80 degrees to strengthen and there is a strong, non-linear response in strength which each degree above 80.
A natural consequence of the enhanced greenhouse effect would therefore be the production of extremely strong hurricanes and we are seeing evidence of this.