Tropical Storm Arthur (2020)

Map plotting the track and the intensity of the storm, according to the Saffir–Simpson scale

On May 12, the National Hurricane Center (NHC) first discussed the possibility of subtropical development north of the Bahamas in the proceeding days related to a broad low pressure system that was expected to form near Cuba.[1] By May 13, thunderstorm activity began to increase in association with a developing trough near the western tip of Cuba, and the NHC considered the developing system to have a 70% chance of subtropical formation in the next five days,[2] although the associated shower and thunderstorm activity was not well organized.[3] Convection began to slowly build around the center by early May 16, and a well-defined low-level circulation (LLC) began to form displaced just slightly east of the main thunderstorms.[4] Based on this, the NHC upgraded the low to Tropical Depression One on the evening of May 16.[5] The system was considered tropical instead of subtropical in nature due to persisting central deep convection and a tight radius of winds.[5]

Satellite image of Arthur's precursor

Based on reports from a Hurricane Hunter aircraft of tropical-storm force winds, the NHC upgraded the system to Tropical Storm Arthur at 03:00 UTC on May 17.[6] Being steered generally north-northeast for the next several hours, Arthur stayed well offshore of the coasts of Florida and Georgia.[7] However, a mid-level trough centered over the United States caused Arthur to slowly be pushed northeastwards over a section of relatively cool waters and as a result most of the storm's convection became limited to the east of the circulation.[8] Despite these unfavorable conditions, reconnaissance aircraft found Arthur slightly stronger, despite its appearance on satellite degrading significantly throughout the past few hours.[9] Deep convection began to swiftly re-develop over the center as the storm began to move over warmer waters of the Gulf Stream, resulting in strengthening.[10] On the afternoon of May 18, Arthur obtained its minimum central pressure of 991 mb (29.3 inHg) and its peak intensity of 60 mph (95 km/h).[11] As Arthur intensified, its center skirted the coast of the Outer Banks in North Carolina, passing a mere 20 mi (32 km) southeast from Cape Hatteras.[12] As a ridge strengthened to the north, Arthur began to be shoved away from the North Carolina coast and an increase in southwesterly shear as well as the beginning of extratropical transition began to separate the storm's main convective activity away from the LLC.[13] The storm completed this process on the morning of May 19, and became an extratropical cyclone as a trailing warm front developed behind the now almost fully exposed LLC.[14]

Arthur on its closest approach to North Carolina on radar on May 18

Although Arthur never directly impacted Florida as a tropical system, the precursor system to Arthur caused heavy rainfall and gusty winds in the Florida Keys and South Florida throughout May 13-14. Over 4 in (101.6 mm) of rain fell in many sections of the Middle Keys and a peak rainfall total of 5.35 in (135.8 mm) fell in Marathon on May 14, where it was the tenth highest rainfall amount for the city on record and second most for May.[15][16] Flash flood warnings were issued for large portions of Miami-Dade County on May 14, where street flooding was reported.[17] Tropical storm-force wind gusts as well as waterspouts prompted the issuance of gale warnings and special marine warnings across the majority of South Florida.[18] Rip currents in Florida led to the water rescues of 70 people in Volusia County, 3 of who were hospitalized.[19] Purple and red flags were raised along the coasts of Georgia and South Carolina to alert the public for rip currents.[20] Offshore Georgia, 3-6 ft (0.9-1.8 m) waves were reported.[21]

The precursor to Arthur dropped heavy rainfall in the Granma Province in Cuba on May 15, including 78 mm (3.07 in) of rainfall in Bayamo in only four hours. These rains resulted in flooded streets and significant damage to homes.[22] In the Bahamas, squalls occurred on Grand Bahama island, where many were still recovering from the adverse effects of Hurricane Dorian. Gusty winds damaged tents and other temporary shelters across the island, and heavy rainfall caused some minimal flooding.[23] However, since the strongest winds of the disturbance were located to the east of the center, damage was limited.[24]

On May 16, tropical storm watches were issued from Surf City to Duck and Pamlico Sound to Albemarle Sound.[25] A day later, these watches were upgraded to tropical storm warnings as Arthur moved closer towards the Outer Banks.[26] By late May 17, rough surf conditions were already being experienced on the southern portion of the Outer Banks.[27] Torrential rainfall occurred as Arthur's outer rainbands scraped eastern North Carolina,[28] with 4.92 in (125 mm) of rain falling in Newport within 6 hours, and many other locations recording at least 3 in (76 mm) of rain from the storm.[29] Tropical storm-force wind gusts in Cape Hatteras were also recorded, although the lopsided nature of the storm kept the strongest winds offshore.[30][28] Wave heights as high as 12.5 ft (3.8 m) were recorded from buoys along the coast of the Outer Banks from Arthur.[31] Due to flooding from Arthur, many highways in the Outer Banks and into mainland North Carolina were closed.[32] SpaceX was also forced to delay the launch of several Starlink internet satellites due to adverse weather from Arthur affecting the recovery fleet.[33] As Arthur moved away from the coast, tropical storm warnings were lifted as conditions gradually improved later in the evening.[34]

• Other storms with the same name
• Hurricane Arthur (2014) – took a similar track and made a landfall in a similar location
• Tropical Storm Ana (2015) – made landfall at a similar time
• Tropical Storm Arthur (1996)  – another storm with the same name and a similar track
• Tropical Storm Beryl (2012) –  the strongest storm to make landfall in the United States in May
• List of North Carolina hurricanes
• List of off-season Atlantic hurricanes

Wikimedia Commons has media related to Tropical Storm Arthur (2020).

• The NHC's advisory archive on Tropical Storm Arthur