On the morning of December 15, containment lines in the Santa Barbara and Montecito areas and protecting nearby homes was the priority, in addition to the threatened Carpinteria and Summerland areas. Officials feared the sundowner winds could push the fire into those communities as they blow south from the mountains down to the coast, and because they also dry out the air. Although they prevented the fire from reaching the community, it still grew to with 40% containment on the morning of December 16, surpassing the Rim Fire in size, and becoming the third-largest wildfire in the modern history of California. Around this time, officials and experts feared that the Thomas Fire could surpass the Santiago Canyon Fire of 1889, which had burned over , and is believed to be California's all-time largest wildfire on record.
