August 9 is before the season heats up, so you shouldn't have anything to worry about. Even in hurricane alley ,we don't worry about them until mid to late August and New York is much cooler. (It takes warm water to spawn hurricanes.)
If there were a hurricane, they would change the itinerary or sail early or late if they absolutely could not sail as scheduled. Last fall one sailing from Florida had to wait out the storm before they could go into port to disembark. Some lucky passengers got a couple of extra days in the sun in the Gulf of Mexico well away from the storm, while others had their cruise cut short by those two days.