What is "Entering Sleep state due to 'Dark Wake Thermal Emergency'" from pmset log?
I found this article from 2011 on MacTech.com reporting that:

"Apple is working on methods to power up select components of a Mac from a sleep state, per a patent at the US Patent &amp; Trademark Office.

Patent number 7996694 is for a "dark wake," or xemplary embodiments of methods, apparatuses, and systems for powering up select components of a computer from a sleep state, maintaining a network state, and powering down the select components of the computer to return the computer to the sleep state are described. For one embodiment, a network interface and a fan controller receive power during the network state maintenance but a display or audio components do not receive power during the network state maintenance. The inventors are Ethan Bold, Stuart Cheshire, J. Rhoads Hollowell, Joe Liu and Dean R. Reece.

Here's Apple's background and summary of the invention: "The various embodiments described herein relate to power management of a processing system. In particular, embodiments include the processing system entering a dark wake state from a from a low power state by powering up select components, maintaining a network state, and returning to the sleep state.

"Computer systems are often used to perform various tasks over a network. When a computer system connects to a network, it establishes a network state with a server or another networked device. In order to make efficient use of network resources, network states may expire and can be periodically maintained or renewed. Additionally, a computer system may periodically update a network state.

"If the computer system is placed in a low power state (e.g., a sleep state), however, the computer system typically terminates the network state (e.g., allows it to expire) or periodically "wakes up" to a full power state (including user-perceptible components such as video and audio), to maintain, renew, or otherwise update an existing network state.

"Exemplary embodiments of methods, apparatuses, and systems for powering up select components of a computer from a sleep state, maintaining a network state, and powering down the select components of the computer to return the computer to the sleep state are described. For one embodiment, the select components include a network interface and do not include a display or audio components. For one embodiment a fan controller receives power during the maintaining of the network state.

"These embodiments allow a system to appear to a user to be asleep while performing maintenance of the network state but also continue to protect the system from overheating by keeping the fan controller on. The fan controller can include subsystems which monitor temperature and determine whether to turn a fan on or off; for example, the fan controller can include temperature sensors and processing logic that determines, using information from the temperature sensors whether to turn on or off a fan or other cooling device in order to protect the system. For one embodiment, the fan controller receives power even while the system is in one or more levels of sleep."

-- Dennis Sellers

It would appear that your computer is performing a Dark Wake, but is unable to maintain good thermal management, possibly due to high ambient temps, and is therefore returning to full sleep for a cool-down period.