Although microorganisms play an important role in biological soil crusts and plant rhizospheres in deserts, it is unclear whether temperature and moisture deep within relatively fast moving hyperarid mobile dunes present a suitable habitat for microbes. To inform this question, we report measurements of temperature and humidity from probes initially sunk below the leeward avalanche face of a mobile barchan dune in the Qatar desert, emerging windward after 15 months of deep burial. Despite large diurnal variations on the surface, temperature within this dune of 5.6 m height is predictable, as long as dune advection is properly considered. It evolves on smaller amplitude and longer timescale than the surface, lagging average seasonal atmospheric conditions by about 2 months. We contrast these deep thermal records with measurements of diurnal variations of the temperature profile just below the surface, which we calculate with a thermal model predicting the relative roles of wind‒driven convective heat transfer and net radiation flux on the dune. Observations and analyses also suggest why random precipitation on the leeward face produces a more unpredictable moisture patchwork on the windward slope. By rapidly reaching sheltered depths, small quantities of rain falling on that face escape evaporation and endure within the dune until resurfacing upwind. At depths below 10 cm, we show that moisture, rather than temperature, determines the viability of microbes and we provide initial microscopic and respiration‒based evidence of their presence below the windward slope.