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Tropical Storm Arthur Forecast Discussion Number 6
2020-05-18 04:56:21| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sun May 17 2020 000 WTNT41 KNHC 180256 TCDAT1 Tropical Storm Arthur Discussion Number 6 NWS National Hurricane Center Miami FL AL012020 1100 PM EDT Sun May 17 2020 Arthur's appearance in radar and satellite imagery has degraded significantly since the previous advisory with very little convective banding features present now. However, an Air Force Reserve reconnaissance aircraft investigating the cyclone late this afternoon and early has found maximum 850-mb flight-level winds of 46 kt in the eastern quadrant along with reliable SFMR surface wind speeds of 36-38 kt, plus a central pressure of 1003 mb. Based on these data, the initial intensity has been held at 40 kt for this advisory since higher wind speeds could be present within areas of convection north of the center that were not sampled. Aircraft and satellite fixes indicate that Arthur has continued to move north-northeastward or 020/09 kt. The cyclone is forecast to accelerate northeastward on Monday ahead of an approaching shortwave trough and frontal system, and remain just offshore of the North Carolina Outer Banks. By Tuesday night, Arthur will be entering the strong mid-latitude Westerlies, which will steer cyclone eastward and also induce extratropical transition when the cyclone merges with the aforementioned frontal system. The new NHC track guidance is tightly clustered about the previous forecast track, so no significant cross-track changes were required. However, some slight changes to the forward were required on days 2 and 3, and the new NHC track forecast now shows Arthur moving a little faster to the east and southeast on those days. Arthur is currently moving over the warmest waters in the Gulfstream where ocean temperatures are 26-26.5 deg C. However, some mid-level shear undercutting the otherwise upper-level outflow pattern, coupled with the entrainment of dry mid-level air has disrupted the overall convective pattern. These unfavorable conditions should continue for the next coupe of days, with only intermittent bursts of deep convection occuring near the center until Arthur passes northeast of the Outer Banks by late Monday. Thereafter, baroclinic effects along with extratropical transition are expected to cause some further strengthening before weakening begins late Tuesday and on Wednesday. The official intensity forecast follows a blend of the intensity consensus model IVCN, and the GFS and ECMWF model forecasts. Key Messages: 1. A Tropical Storm Warning is in effect for a portion of the North Carolina coast. Tropical-storm-force winds and heavy rains are expected there on Monday. 2. Dangerous coastal surf conditions and rip currents are expected to spread northward along the southeast U.S. coast to the mid-Atlantic states during the next couple of days. See products from your local National Weather Service Forecast Office for more details. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 32.4N 76.9W 40 KT 45 MPH 12H 18/1200Z 34.0N 75.6W 40 KT 45 MPH 24H 19/0000Z 35.8N 73.2W 45 KT 50 MPH 36H 19/1200Z 36.4N 70.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 20/0000Z 36.0N 67.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 20/1200Z 35.0N 66.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 21/0000Z 33.8N 64.6W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 22/0000Z 31.6N 62.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 23/0000Z...DISSIPATED $$ Forecaster Stewart
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