Karen — 2025

A non-tropical low formed downstream of an upper-level trough on 8 October 2025 and transitioned into Subtropical Storm Karen by 1200 UTC 9 October about 300 nautical miles northwest of the northernmost Azores (near 43.5°N, 34.8°W). Karen existed as a subtropical cyclone from 9–10 October, then weakened to a post-tropical remnant low and dissipated by 11 October. Its track carried it northeastward across the central North Atlantic at high latitudes before merging with surrounding mid-latitude flow. Karen made no landfalls. It developed and remained well offshore of the Azores and other land areas; no coastal watches or warnings were issued. Karen’s maximum sustained winds were 40 knots (about 46 mph) and its estimated minimum central pressure was 998 mb. The NHC classified it as a subtropical storm at its peak intensity; scatterometer and satellite estimates supported the 40 kt peak. Because Karen remained over the open ocean and well north of land, there are no reported storm surge measurements or rainfall totals at populated locations in the report. Sea-surface temperatures where it formed were unusually cool for cyclone formation (about 20–22°C), and the system developed in a large mid-latitude environment rather than over warm tropical waters. There were no reports of damage or casualties associated with Karen. The storm is notable for forming at 43.5°N, the farthest north in NHC records for genesis of a tropical or subtropical cyclone. Forecasts had limited lead time for genesis—Karen’s precursor was placed in the Tropical Weather Outlook only 12 hours before the subtropical transition—and global models struggled to predict the convective and structural changes that led to formation. Official short-term forecasts while the storm existed had relatively small track and intensity errors.