On 10 October, a tropical depression to the south of Spain organised into Storm Callum. Callum moved further northeastward while strengthening in particularly favourable conditions along with low wind shear. The system then underwent explosive cyclogenesis, as it was forced toward the United Kingdom by a jet stream. On 11 October, Callum began to show signs of an eye as it reached its peak intensity on approach to Cardiff, Wales. Only then did it encounter colder waters and the low-level eye was exposed to westerly wind shear, which had an adverse effect on Callum before it made impact on land. The system then brought intense winds with speeds of up to 76 mph (122 km/h) to parts of northern England, along with torrential rains to parts of Wales with 95. 6 mm (3. 76 in) recorded in Libanus but overall only made a minimal impact on land. Unexpected warm weather was reported soon after, with Donna Nook in Lincolnshire reaching 26. 5 degrees Celsius in the afternoon. At 21:00 UTC, colder water surface temperatures and high vertical wind shear affected Callum, and the system soon transitioned into an extratropical cyclone. Callum subsequently moved across Iceland and the Norwegian Sea as a weakened system, continuing northwards into the Arctic and out of the basin by 16 October.