Subtropical Event 1 formed in Mid-January off the Northeast U.S. Coast
Fig. 1-2: An area of deep low pressure off the Northeast U.S. Coast in mid-January is reviewed by NOAA/NHC and determined a subtropical storm, the first of 2023. In this zone, SSTA were in the +6C to +7C range (60’sF).
Discussion: On May 11th, NOAA/NHC determined an intense storm off the Northeast U.S. Coast gained subtropical characteristics and is considered the first event of the 2023 season. The next storm will be identified as AL02 although given the name Arlene if intensification occurs. Of interest, is an aspect of climate change related to this event. Since about 10 years ago, northeast North America and Greenland ice and snow melt has accelerated causing a semi-permanent stratified cool pool of ocean water in the Labrador Sea to south of Greenland. This feature is known as the North Atlantic warm hole (NAWH). The NAWH is most clearly identified during the early-to-middle warm season. This feature is having tendency to block northeast progress of the Gulf Stream forcing the piling of warm water off the Northeast Coast of the U.S. Subtropical Storm 1 formed over water in the 6-7C warmer than normal range (in the 60’s) with 70’s not far to the south.
The official message from NOAA/NHC follows…
…NHC Determines That a Subtropical Storm Formed in the Atlantic Basin in Mid-January 2023… Through the course of typical re-assessment of weather systems in the National Hurricane Center’s (NHC) area of responsibility, NHC hurricane specialists have determined that an area of low pressure that formed off the northeastern coast of the United States in mid-January should be designated as a subtropical storm. Specific information on the justification for the subtropical storm designation, as well as the system’s synoptic history and impacts, will be available in a Tropical Cyclone Report, which will likely be issued during the next couple of months. This subtropical storm is being numbered as the first cyclone of 2023 in the Atlantic basin and will be given AL012023 as its system ID. As a result, the next system that forms in 2023 in the Atlantic basin will be designated as AL022023, and advisories will be issued in AWIPS bin 2 (e.g., Public Advisories will be issued under AWIPS header TCPAT2 and WMO header WTNT22 KNHC). If the system begins as a tropical depression, then it would be given the designation ‘TROPICAL DEPRESSION TWO’, and if it becomes a tropical storm, it would be given the name ‘ARLENE’. National Weather Service policy (through NWS Instruction 10-607, Section 1) allows for marginal subtropical systems to be handled in real-time as non-tropical gale or storm events in NWS High Seas Forecast products. This was the procedure followed for the unnamed subtropical storm in mid-January. However, the lack of real-time issuance of advisories does not preclude NHC from retroactively designating these systems as a subtropical cyclones in post-analysis, if necessary.