The North Atlantic’s first tropical depression of 2020 developed Saturday evening – Tropical Depression One. The formation of TD One makes 2020 the sixth consecutive year in which the Atlantic basin has had tropical or subtropical cyclone activity prior to the official start of the season (June 1). 2020 is also the third straight year with a May subtropical or tropical cyclone, and five of the last six years have had May activity in the Atlantic basin. TD One is likely to strengthen into Tropical Storm Arthur by Sunday morning, and could bring Tropical Storm conditions to the North Carolina Outer Banks. TD One could become the fourth storm named Arthur to impact the North Carolina Outer Banks, as three previous storms named Arthur (1996, 2002 and 2014) have passed very close to the Outer Banks region.

As of 8:00 p.m. EDT Saturday, Tropical Depression One was centered near 28.9°N 77.9°W, and was moving northeastward at 14 mph. Maximum sustained winds were 30 knots (35 mph), with an estimated minimum pressure of 1006 mb. An Air Force Hurricane Hunter aircraft is currently investigating the depression, and recent observations suggest TD One is on the verge of tropical storm status. Since deep convection has coalesced around the center of the depression, the National Hurricane Center (NHC) decided to go with a tropical, rather than subtropical, classification. This makes 2020 the first Atlantic hurricane season to start with a tropical formation since 2014. The depression is gradually getting better organized, though the center appears to be on the southwestern edge of the convection. The center appears to be much more defined than this morning.

The environment for TD One appears to be conducive enough for at least some slight intensification. Based on the 18z Saturday run of the SHIPS model, wind shear is expected to remain low (less than 15 knots) for the next 48 hours, which favors intensification. However, since it is only May, sea surface temperatures are marginal – about 25°C (77.2°F). In addition, mid-level relative humidity values are forecast to be near 50 percent, which could result in occasional continental dry air intrusions. Regardless, the environment appears conducive for some intensification, and it is likely that TD One will become at least a moderate tropical storm by Monday as it heads north-northeastward. The model guidance disagrees with the exact track of TD One. The ECMWF and UKMET models are farther east, keeping TD One’s center offshore. The GFS and HWRF models are farther west, showing a landfall over the North Carolina Outer Banks as a moderate to strong tropical storm. The NHC forecast is a consensus of the two, and predicts TD One will turn to the east and lose tropical characteristics on Tuesday. Because of the possibility of tropical storm conditions, a Tropical Storm Watch has been issued for parts of the North Carolina coast from Surf City to Duck, as well as the Pamlico and Albemarle sounds.

I will be back with an update on TD One (likely to be TS Arthur by that time) tomorrow.