This chapter presents 25 meteorological and two seismic phenomena noted in the correspondence of the Late Byzantine period. It investigates the various reasons why they are documented in the letters, how they were perceived, as well as the author’s experiences during these events. In the Late Byzantine period, the climate was shaped by the conditions that prevailed during the transition from the so-called Medieval Warm Period (MCA, ca. 9th/10th to ca. 13th century) to the “Little Ice Age” (LIA, ca. 13th–19th century). In the introduction of the present chapter we present the current state of the art on these climatic variations. Unfortunately, the incidents recorded in the epistolography do not allow a broader view, beyond the local or, sometimes, regional picture. The observations on these phenomena are presented in either lengthy or short accounts and demonstrate that in the epistolography most cases concern incidents at sea and tempests experienced by the letter-writers when voyaging on ships.