Theta (2020)

Theta formed from a non-tropical low in the central Atlantic and was first classified as a subtropical storm on 10 November 2020 about 855 nautical miles southwest of the Azores. It moved generally eastward and east‑northeastward along the southern edge of the mid-latitude westerlies from 10–15 November, occasionally shifting northeastward for short periods. Convection waxed and waned as dry air and wind shear affected the system; Theta weakened to a tropical depression early on 15 November about 105 nautical miles southwest of Madeira and became a remnant low later that day, with the remnants absorbed by a mid‑latitude cyclone on 16 November.

Theta did not make any landfalls. It remained well over the open northeastern Atlantic and did not produce coastal warnings from the U.S. or require formal coastal watches or warnings; marine advisories were issued by the Meteorological Service of Spain for areas near the Canary and Madeira Islands.

The storm’s maximum sustained winds reached 60 knots (about 69 mph) and the minimum central pressure was 987 mb. At peak intensity on 10 November the cyclone was classified as a 60‑kt system and is shown in the official record transitioning from subtropical to tropical character during that period.

Observed storm surge and rainfall impacts were negligible in the official record. There were no surface observations of tropical‑storm‑force winds tied to Theta, and the report contains no notable storm surge or large rainfall totals for cities or counties; only marine areas received advisories.

There were no reports of damage or casualties associated with Theta. The report notes that genesis was not well forecast: the pre‑existing non‑tropical low was anticipated days earlier, but its development into a subtropical or tropical cyclone was given only a low chance until roughly a day before formation. Official track forecasts performed better than recent averages, while some intensity forecasts had a high bias as Theta weakened slightly faster than predicted.