Take it in now before it gets worse and they will probably flush the heater core out, replace the water pump, replace the thermostat, or find a head problem. I have seen all those issues cause this, but having it diagnosed is the first step.
2013 JKU Sport, billet, auto, 3.73, LSD, 315/75/16 Duratracs on MB 72, 10A springs, Bushwacker flatties
Sold - 2005 TJ, red, auto, 3.73, 33" Duratracs, 4" lift
Ice storm casualty in 2007 - 2003 TJ, green, auto, 3.73, 33" Duratracs, 4" lift