The warmer months there are more baitfish in the shallow water and hence more fish. December and January are good months to fish but the weather is the key. Cold fronts can put a damper the best of efforts this time of year. When we have stable weather the fishing can be great. On the other hand the largest snook that I ever had a customer catch was on a day that I tried to cancel because of a cold front and approaching rain.
Cobia are here all of the warmer months.
They are a pelagic species that roams around all over. It is not uncommon for people to catch them 100 miles offshore or in 2' of water cruising the shallows. We catch most of them while we are tarpon fishing. Charlotte Harbor holds lots of these big fish. Generally speaking we fish for what is biting the best.