Karen — 2025

Subtropical Storm Karen formed at 43.5°N, 34.8°W, about 490 miles northwest of the Azores on October 9, about 300 nautical miles northwest of the northern Azores. It developed from a non-tropical frontal low and lasted as a named storm through October 10, then weakened to a low and dissipated on October 11. Karen moved generally northeast, then east-northeast, over the open Atlantic. Its formation location was the farthest north recorded for a tropical or subtropical cyclone in NHC records. Karen reached its peak strength when it formed: maximum sustained winds of 40 knots, or about 46 mph, and a minimum central pressure of 998 millibars. It remained a subtropical storm, not a hurricane, and did not rapidly intensify. The peak estimates were based in part on satellite measurements and intensity estimates. Karen made no landfalls. It stayed well offshore, and no coastal watches or warnings were issued. The report gives no notable storm-surge heights or rainfall totals; it reports no damage or casualties. The report records no deaths, direct or indirect, and no damage associated with Karen. Its unusual high-latitude formation over cool ocean water was noteworthy. NHC genesis forecasts identified the general area well, but Karen’s formation was poorly predicted in advance: the outlook first mentioned the system 12 hours before formation and never raised the chance of formation to the medium or high categories. Only two NHC forecasts were available for verification; their 12-hour track and intensity errors were below the average errors for the preceding five years.