Water weight or fat gain?

Hey there! I just got back from a vacation (4-day cruise in the Bahamas and 3 days in Florida) last night. It was EXTREMELY hot and HUMID everyday and night, dropping only to the 80s at night. I'm originally from California, so I'm not used to the humidity, so is it possible for the 5 pounds I gained to be from the sudden heat and humidity? We also flew for around 7-8 hours yesturday as well. I watched what I ate all the time, but I did up my caloric intake the whole time, so I'm pretty sure I gained about 1-2 pounds of extgra weight. But is it possible for the rest to be swelling? If so, how can I get rid of it quickly?