As stated a tidally locked world that has complete 1:1 begins to spin slowly. It starts slowly, a 2:1 ratio that steadily ramps up over the course of a month to one rotation every month, which would eventually continue increasing exponentially until it reaches an Earth-equivalent resonance (365 days in a year, approximately.) What sort of natural disasters occur on this world not related to the sudden loss of sunlight/appearance of it in either half of the globe?
Some other information: The night-half of the planet is covered in a singular, hemisphere-wide icecap comprised of 70% of the planets water at -60 celsius from 90* S to approximately 10* N (correct me if an earth-like planet would be warmer at that latitude). There is a band of highly volcanic land on the terminator caused by tidal stresses. For comparison points, there are currently 400-500 mph windstorms resulting from the thermals on this planet, it would be nice to see if disasters would be better or worse than those. Portions of the terrestrial planet have abnormally thin crust comparable to oceanic plates. There are reasons for this not related to the question.
Edit: Given the information in the replies, here is more helpful information: suppose the speed up was slowed to a gradual increase in speed per year, about an hour every year so that in 500-600 years the planet would have one or two week long day cycles after the initial one month start-up. How would the cataclysm differ from the above with this information?
There is also constant cloud cover on the nightside sustained by atmospheric condensation. Can this prevent heat radiating into space from that side?
Lastly most natural life on the planet evolved fro m extremophiles to A) avoid regular disasters through regular mass migration and B) survive temperature extremes, as well as to possess the bare minimum of genetic complexity for an average-sized lifeform for another reason not important to the discussion.
Otherwise I am quite satisfied with the information I have received, I just need to find a process to sustainably slow the planetary "jumpstart."