NOTE: This post concerns a subtropical storm of the 2023 Atlantic hurricane season which formed in January of that year, but was not identified at the time. Reanalysis confirmed that it was in fact a subtropical cyclone a few months later. Since it was not named, the naming of storms later in the season began with "A" (see Tropical Storm Arlene), but the numbering of subsequent tropical depressions began with "Two".
On January 14, a trough became separated from a larger frontal boundary just off the U.S. east coast. A well-defined but non-tropical low formed off the mid-Atlantic states the next day. Water temperatures over the Gulf stream, while cold, were much warmer than normal for the region, allowing deep convection to develop. This lead to the formation of a subtropical storm around the morning of January 16. The cyclone underwent significant deepening that next day and turned northeast, then north. It reached a peak intensity of 70 mph sustained winds and a central pressure of 976 mb late on the 16th. During the morning of January 17, the cyclone made landfall in far eastern Nova Scotia, with estimated sustained winds of 50 mph at landfall. The storm continued northward, became post-tropical later that day, and dissipated on the 18th.
The image above shows the unnamed subtropical storm on January 16, with a distinct, eye-like feature.
The 2023 unnamed subtropical storm had the lowest central pressure of any January tropical or subtropical cyclone ever observed in the Atlantic.
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