|Above: Subtropical Storm Rebekah as seen by the MODIS instument on the Aqua satellite late Wednesday afternoon, October 30, 2019. Image credit: NASA.|
The persistent Atlantic hurricane season of 2019 continues to sputter on, thanks to the formation of Subtropical Storm Rebekah late Wednesday afternoon. Rebekah formed in the northeast Atlantic, 745 miles west of the Azores Islands, in a location similar to where Hurricane Pablo formed last week.
At 5 pm EDT October 30, Rebekah was a low-end subtropical storm with 45 mph winds, headed east at 13 mph towards the Azores. Like Pablo, Rebekah formed over a region with very chilly sea surface temperatures (SSTs) near 21°C (70°F)—far below the conventional threshold for tropical development of around 26°C (79°F), and slightly below the more recently discovered value of 22.5°C (72.5°F) for hybrid/subtropical development. However, very cold upper air associated with an upper low made the atmosphere very unstable, giving Rebekah the boost it needed to develop a solid area of heavy thunderstorms and become a subtropical storm. Satellite images on Wednesday evening showed that Rebekah was holding roughly steady in intensity.
Though Rebekah formed on Devil's Night, the storm is not expected to cause much deviltry. Rebekah will be crossing into a region with cool SSTs, higher wind shear, and drier air on Friday, which will likely convert it into an extratropical storm. Rebekah is not expected to be a threat to any land areas as a named storm, but could affect the Azores as an extratropical storm on Friday.
Rebekah’s formation brings the Atlantic tally for 2019 to 17 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE index of 122.9. The 1981 – 2010 averages for these quantities by October 30 were 11.1 named storms, 5.8 hurricanes, 2.5 intense hurricanes, and an ACE index of 97.7, according to Dr. Phil Klotzbach, so 2019 is above average in all metrics.
According to Dr. Klotzbach, only six other seasons have had 17+ named storms by October 30: 1933, 1995, 2005, 2010, 2011 and 2012. Rebekah became a named storm at 38.3°N—the farthest north that an Atlantic named storm has formed this late in the calendar year since Subtropical Storm Two developed on December, 9, 1975. Klotzbach also noted that 7 of the first 16 Atlantic named storms in 2019 lasted 24 hours or less as a named storm—the most extremely short-lived named storms on record, breaking the old record of 6 set in 2005.