by Ken McKinley
The official start of the Atlantic hurricane season is June 1st each year, but this does not mean that tropical or subtropical cyclones cannot occur before this date. Historically the peak of the season occurs later in the summer and into the early autumn, and it is not unusual to see long periods of no activity early in the season, though in recent years the first tropical system has shown up in either May or June.
2023 has been no exception as the first tropical cyclone of the season (Arlene) formed in early June. This system began as a tropical depression on the afternoon of June 1st, and those who were paying close attention may have noticed that it was designated as Tropical Depression 2. This begs the question: What happened to number 1?
The National Weather Service is continually examining the large quantities of data that it gathers, even once this data is no longer fresh. The process of “reanalysis” is used to help gain a better understanding of weather systems, particularly those that have had a great impact on human activities. The process allows a more careful examination of the data record, and can include data that was not available in real time. Sometimes this process results in slight changes in the classification of systems. As an example, hurricane Andrew which struck Florida and Louisiana in 1992 was changed to a category 5 hurricane more than 10 years after its occurrence. In real time, the system was designated as a category 4 system at its peak, but the more careful analysis of the data was used to make the change.
In January of 2023 a strong low pressure system which formed in the Atlantic off the northeastern U.S. upon reanalysis was determined to
have become a subtropical storm for a period of time. This therefore became the first system of the year, and even though advisories were not issued for the system in real time, it has received the designation of the first tropical or subtropical system of the year. A full report will eventually be issued for the system (as is the case for all tropical and subtropical cyclones) so the number 1 designation is important for that reason.
Figure 1 shows the surface analysis chart for 14 January 2023 at 1800 UTC, and a complex area of low pressure is clearly evident in the western Atlantic with several associated fronts. Figure 2 is a satellite image of the Atlantic at 1740 UTC on 14 January, and the large majority of the clouds are associated with the frontal boundaries, generally east of 70W, though there is some cloudiness wrapping around the low center to the east of North Carolina and the Chesapeake region.
24 hours later at 1800 UTC 15 January 2023 the surface analysis (Figure 3) indicated a more consolidated low center near 37N/69W with an occluded front extending northeast to near 41N/64W, and a warm front extending northeast from that point with a cold front extending off to the south-southeast. The satellite image at about that same time (Figure 4) indicated a small compact circulation around the low center with more significant clouds to the east of the cold front and north of the warm front. This may have indicated that the system was in the process of becoming detached from the fronts and starting to acquire the characteristics of a subtropical storm at that time.
By 1800 UTC 16 January 2023, the surface analysis (Figure 5) indicated a compact low center at about 38N/64W with no fronts near it. The occluded, warm and cold fronts were all displaced well to the north and east of the low center at that time. The corresponding satellite image (Figure 6) showed a very clear circulation associated with the low, and most of the frontal clouds will off to the north and east, and at this time the low was likely a subtropical storm.
This is only a small portion of the data that goes into the reanalysis process, and when the full report on this system is issued (likely later this year) details regarding the time the system became a subtropical storm and its track and intensity will be included.
Going back to the start of the 2023 season, after Arlene, Tropical Storm Bret and Tropical Storm Cindy have both formed. At this writing, Bret has entered the Caribbean Sea, and
Cindy is moving west-northwest over the central tropical Atlantic. Both of the systems formed in the eastern Atlantic which is unusual for this early in the season. Typically the sea surface temperatures in this part of the ocean do not become warm enough for tropical cyclone formation until later in the season. Both of these systems are likely to encounter stronger upper level winds in the coming days leading to weakening. One of the byproducts of a well established El Nino in the Pacific (which is present this year) tends to be stronger upper level winds in the tropical Atlantic which can suppress hurricane development. The combination of the warmer than normal sea surface temperatures and the stronger than normal upper level winds provides a mixed signal for this year’s Atlantic hurricane season.
Ken McKinley is an ON contributing editor and is a weather router and owner of Locus Weather based in Camden, Maine.