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Tropical Storm Arthur Forecast Discussion Number 2
2020-05-17 04:53:55| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sat May 16 2020 127 WTNT41 KNHC 170253 TCDAT1 Tropical Storm Arthur Discussion Number 2 NWS National Hurricane Center Miami FL AL012020 1100 PM EDT Sat May 16 2020 An Air Force Reserve reconnaissance aircraft that has been investigating the tropical cyclone east of Florida has recently found maximum 925-mb flight-level winds of 45-46 kt to the southeast and east of the center, which equates to surface winds of 34-35 kt, along with uncontaminated SFMR surface wind speeds of 33-36 kt. Based on these data, the depression has been upgraded to Tropical Storm Arthur, the first named storm of the 2020 Atlantic hurricane season. The initial motion estimate remains north-northeastward or 030/11 kt. Arthur made a slight northeastward jog earlier this evening, but now appears to have returned to its previous base course. A motion toward the north-northeast is forecast to continue for the next 24 hours or so, keeping the cyclone well offshore the coasts of Florida and Georgia. A sharp shortwave trough currently moving across the southern Plains is forecast to dig east-southeast to southeastward over the next 48 hours, which will act to accelerate and eject Arthur more poleward. The more the shortwave trough digs and loses latitude, the more Arthur could get pulled closer to the North Carolina Outer Banks as per the GFS and HWRF scenarios. In contrast, the ECMWF and UKMET models show the shortwave losing amplitude quickly and lifting out, which acts to push Arthur farther away from the United States east coast. For now, the new NHC forecast track closely follows the various consensus models, which are about midway between the GFS-HWRF and ECMWF-UKMET solutions. However, the track was adjusted slightly to the right of the previous advisory track due mainly to the more eastward initial position. It should be noted that forecast track uncertainty is typically larger for weak systems like Arthur. Arthur has moved off of the warm waters of the Gulfstream current and currently is passing over a cold pool with SSTs near 24.5 deg C. These cooler waters should prevent any significant strengthening in the very near term. By 24 hours however, the cyclone is forecast to pass back over the warmer waters of the Gulfstream while moving into a very low vertical wind shear regime. These conditions, coupled with some cooler air aloft, should allow more vigorous convection to develop near the center, resulting in more strengthening as Arthur passes near the North Carolina coast. Extratropical transition should occur in about 48-60 hours over the much cooler waters of the North Atlantic. The NHC intensity forecast follows a blend of the consensus models HCCA and IVCN, and is similar to the previous intensity forecast. Key Messages: 1. A tropical storm watch is in effect for a portion of the North Carolina coast. Tropical-storm-force winds and heavy rains are possible there on Monday. 2. Dangerous coastal surf conditions and rip currents are expected to spread northward from Florida to the mid-Atlantic states during the next few days. See products from your local National Weather Service Forecast Office for more details. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 29.4N 77.7W 35 KT 40 MPH 12H 17/1200Z 30.5N 77.2W 35 KT 40 MPH 24H 18/0000Z 32.2N 76.4W 40 KT 45 MPH 36H 18/1200Z 34.1N 75.2W 45 KT 50 MPH 48H 19/0000Z 36.2N 73.0W 45 KT 50 MPH 60H 19/1200Z 37.5N 70.6W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 20/0000Z 38.0N 69.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 21/0000Z 38.0N 67.6W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 22/0000Z...DISSIPATED $$ Forecaster Stewart
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