During the second week of May, a cold front stalled over the western Atlantic, its southwestern end threading the Florida Straits. Over the next few days, wet weather prevailed in that region and a broad circulation became evident around May 14. The same day, torrential rains soaked extreme south Florida and the Keys, with lesser impacts in Cuba and the Bahamas. The system moved northeast but lacked deep convection until May 16, when the center of circulation became better defined east of the Florida peninsula. That afternoon, it was classified Tropical Depression One.
The depression became rather asymmetric that evening, with nearly all thunderstorm activity in a semicircular band east of the center. Nevertheless, winds increased enough for it to become Tropical Storm Arthur, the first named storm of the 2020 season. 2020 therefore marked the sixth consecutive year in which a storm formed before the official start of hurricane season on June 1, a new record streak. Arthur churned steadily north-northeast through May 17. Its circulation became better defined as shear lessened, but cooler ocean waters limited convective activity, leading to just a bit of strengthening that day. Rainfall began that evening in eastern North Carolina as Arthur approached.
Near the coast, the storm encountered a deep pool of warmer water in the Gulf stream and strengthened some more. On May 18, Arthur passed just east of Cape Hatteras with peak sustained winds of 50 mph. By that time, the thunderstorm activity in the western semicircle had improved significantly, leading to heavy rains over a large swath of the coast and sustained tropical storm force winds in at least the easternmost barrier islands. The mid-latitude westerlies grabbed hold of Arthur, however, and accelerated it northeastward away from land that evening. Baroclinic processes strengthened the storm a bit more as it underwent extratropical transition overnight, bringing Arthur to its peak intensity of 60 mph sustained winds and a minimum pressure of 991 mb. It turned toward the east and became post-tropical during the morning of May 19. The remnant system turned sharply south later that day and angled toward Bermuda, but weakened to an extent that it brought only intermittent showers and gusty winds as the center passed the island on May 20. It dissipated shortly afterward.
The above image shows Tropical Storm Arthur just off the coast of North Carolina.
Arthur did not quite make landfall, but it brought heavy rain to south Florida as a tropical disturbance (before formation) and the Cape Hatteras region.
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