I bought a Yuasa 51319 battery just over a year ago plus I live in a warm climate. Surely the battery can't be on it's way out?
as pointed out already, you can't make that assumption. Motorcycle batteries are infamous for erratic life spans.
The basics are simple:
1) The battery is discharging internally
2) The battery is discharging externally.
Case 1 is easy, but annoying: replace the battery.
Case 2, not so easy.
I'd probably start by looking at the battery itself -- if dirty, you could be discharging through the dirt, 'specially if there's some dampness around.
Next, I'd disconnect the battery, and slip in an ammeter. The power here should be pretty low, but I'd still suggest starting at a 10A range until you are sure -- some meters will happily blow a fuse if you run 300ma through a 100ma range, which may be difficult to replace.
All that should be drawing power at this point is your ignition computer, the audio system, and the alarm system. The power draw should be pretty low -- even 50ma (0.050A) will be 1.2AH of energy sucked off your battery in 24 hours, which is a non-trivial chunk of the battery's total capacity (and remember: if you have a 20AH battery, that means you have 20AH of energy to suck off the thing before it is stone dead, not 20AH and then you can start your bike!).
If your draw seems high here, reconnect the battery, and check the draw through every fuse (use your meter to replace the fuse). The circuit attached to the fuse with high draw is where the power is going.
I have seen cases where (supposedly) low power circuits work great...but suck more power when idle than they should. Repair can be expensive and may not be worth it -- battery tenders are cheap.