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Tropical Storm Arthur Forecast Discussion Number 10
2020-05-19 04:52:14| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Mon May 18 2020 000 WTNT41 KNHC 190252 TCDAT1 Tropical Storm Arthur Discussion Number 10 NWS National Hurricane Center Miami FL AL012020 1100 PM EDT Mon May 18 2020 Arthur's cloud shield has shifted to the left or north side of the cyclone's direction of motion since the previous advisory, which is a distinctive sign of a tropical cyclone beginning to lose its tropical characteristics, especially now due to the cyclone moving over 23 deg C sea-surface temperatures. However, there remains enough convection within 45-75 nmi of the center for Arthur to still be classified as a tropical cyclone. The initial intensity has been increased to 50 kt based on a recent 0129 UTC ASCAT-B overpass that indicated several 50-51 kt wind vectors existed in the northwestern quadrant. The initial motion estimate is 070/13 kt. Arthur should move east- northeastward tonight and then turn toward the east by Tuesday morning as the cyclone moves around the northern periphery of a low- to mid-level ridge. On day 2, all of the global models are forecasting the mid- and upper-level circulations to separate from the low-level circulation, with the latter feature dropping southeastward and then southward around the eastern portion of a low-level ridge. The new track forecast is similar to but slightly east of the previous advisory track on days 2 and 3, and closely follows a blend of the consensus models TVCN and GFEX. Only slight strengthening is expected during the next day or so due to baroclinic effects while Arthur undergoes extratropical transition. Data from NOAA Buoy 44014, located west Arthur's center, indicate that a cold front passed over that station around 2300 UTC, which would place the front about 50-75 nmi west of the cyclone at this time. Therefore, a merger with the front is likely during the next 12 hours. The system should begin to steadily weaken shortly after 24 hours when Arthur will be moving over SSTs near 20 deg C, and in conjunction with the aforementioned decoupling of the circulations. Dangerous coastal surf conditions and rip currents are expected to continue along portions of the mid-Atlantic and southeast U.S. coasts 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 19/0300Z 36.4N 72.4W 50 KT 60 MPH 12H 19/1200Z 36.9N 70.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 24H 20/0000Z 36.4N 67.3W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 20/1200Z 35.2N 65.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 21/0000Z 33.7N 64.6W 40 KT 45 MPH...POST-TROP/EXTRATROP 60H 21/1200Z 32.3N 64.4W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 22/0000Z 30.9N 64.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 23/0000Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm Arthur Forecast Discussion Number 9
2020-05-18 22:39:41| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon May 18 2020 630 WTNT41 KNHC 182039 TCDAT1 Tropical Storm Arthur Discussion Number 9 NWS National Hurricane Center Miami FL AL012020 500 PM EDT Mon May 18 2020 Although the center of Arthur did not make landfall in the North Carolina Outer Banks, it passed within about 20 n mi southeast of Cape Hatteras around 1500 UTC. Tropical-storm-force wind gusts have been reported at several automated observing sites on and near the Outer Banks, with the highest sustained wind of 34 kt at Alligator River Bridge earlier this afternoon. Deep convection continues over the northeastern portion of Arthur's circulation, but visible imagery has recently shown an increase in separation between low-level center and the convective activity. This is the result of increasing southwesterly shear and the beginning of the cyclone's extratropical transition. The initial intensity remains 45 kt, which was in agreement with the earlier aircraft data. As the cyclone completes its extratropical transition, some strengthening is forecast due to baroclinic processes. After 24 hours, little change in strength is expected until the frontal gradients decrease on Wednesday. The system should gradually spin down after that time, and dissipate by late in the week. The initial motion estimate is 045/14 kt. Arthur should continue northeastward this evening, but is expected to turn eastward Tuesday morning as the cyclone becomes embedded within the mid-latitude westerlies. Troughing over the central and western Atlantic should cause the Arthur to turn southeastward on Wednesday when the steering flow becomes northwesterly. Little change was required to the previous NHC official forecast and the updated track again lies between the GFS, ECMWF, and the multi-model consensus. Dangerous coastal surf conditions and rip currents are expected to continue along portions of the mid-Atlantic and southeast U.S. coasts 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 18/2100Z 36.1N 73.9W 45 KT 50 MPH 12H 19/0600Z 36.9N 71.6W 50 KT 60 MPH 24H 19/1800Z 37.0N 68.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 20/0600Z 36.2N 66.8W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 20/1800Z 34.8N 65.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 21/0600Z 33.0N 64.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 21/1800Z 31.5N 64.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 22/1800Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Arthur Forecast Discussion Number 8
2020-05-18 16:42:38| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Mon May 18 2020 000 WTNT41 KNHC 181442 TCDAT1 Tropical Storm Arthur Discussion Number 8 NWS National Hurricane Center Miami FL AL012020 1100 AM EDT Mon May 18 2020 Arthur has become a little better organized this morning with an overall increase in convection and banding noted since overnight. The first couple of reconnaissance aircraft passes through the center have shown that the pressure has fallen to around 996 mb. The plane has also reported several believable SFMR winds of 38-43 kt, and the anemometer on buoy 41025 at an elevation of only 4 m has reported a peak 1-minute wind of 37 kt. Based on these data the initial intensity is set at 45 kt. The forward speed of Arthur has continued to increase and the estimated motion is north-northeast at 14 kt. The cyclone should turn northeastward later today and begin moving away from the North Carolina Outer Banks as a mid-latitude trough approaches from the west. By Tuesday, Arthur is forecast to turn eastward within the mid-latitude westerlies. After that time, a deepening trough over the central and western Atlantic is expected to cause the cyclone to turn southeastward as the steering flow turns northwestward. The GFS and ECMWF are now in relatively good agreement on this scenario and the new NHC track forecast lies between those typically reliable models and the multi-model consensus aids. Although the vertical shear is increasing over the storm and it is soon moving over cooler waters, some strengthening due to baroclinic process is predicted over the next 24 hours. The storm should merge with a frontal boundary late tonight or early Tuesday which will complete Arthur's transition to an extratropical cyclone. By Wednesday, the post-tropical cyclone should begin to weaken as the frontal gradients decrease. The post-tropical cyclone should dissipate in about 96 h. 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 today. 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 18/1500Z 35.1N 75.2W 45 KT 50 MPH 12H 19/0000Z 36.4N 73.3W 50 KT 60 MPH 24H 19/1200Z 37.2N 70.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 20/0000Z 36.8N 67.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 20/1200Z 35.5N 65.8W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 21/0000Z 34.0N 65.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 21/1200Z 32.0N 64.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 22/1200Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Arthur Forecast Discussion Number 7
2020-05-18 10:36:00| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Mon May 18 2020 000 WTNT41 KNHC 180835 TCDAT1 Tropical Storm Arthur Discussion Number 7 NWS National Hurricane Center Miami FL AL012020 500 AM EDT Mon May 18 2020 Arthur remains poorly organized in both satellite and radar imagery this morning, with the low-level center located near the southwestern edge of a complex of ragged convective bands. Surface observations from buoys off of the North Carolina coast suggest the central pressure has fallen a little since the last aircraft fix, so the intensity will be held at 40 kt for this advisory. The next aircraft is scheduled to reach Arthur between 11-12Z. Arthur's forward speed has increased with the initial motion now 020/12. A baroclinic trough and associated surface front approaching from the west should cause Arthur to turn northeastward during the next several hours, with the forecast track showing the center passing near or just offshore of the North Carolina Outer Banks. By Tuesday and Tuesday night, Arthur will be entering the strong mid-latitude Westerlies, which will steer cyclone eastward for a day or two. After that time, Arthur or its remnants should turn southeastward and southward on the southwest side of a deep-layer trough over the central Atlantic. The latest guidance is showing a more southward motion after 60 h than seen previously, and the new forecast track is also nudged southward during that time. Arthur is moving near and almost parallel to the Gulf Stream, and the warm water could allow some strengthening before southwesterly shear increases significantly later today. The cyclone should merge with a frontal system and become extratropical in the 24-36 h period, with the global models indicating some increase in the winds north of the center as this occurs. The intensity forecast calls for Arthur to reach a 50 kt intensity in 36 h as an extratropical low in best agreement with the GFS model. After 48 h, the system should decay, and the global models suggest it should dissipate in the 96-120 h period. The new intensity forecast has only minor tweaks from the previous forecast. 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 today. 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 18/0900Z 33.5N 76.6W 40 KT 45 MPH 12H 18/1800Z 35.2N 74.9W 45 KT 50 MPH 24H 19/0600Z 36.5N 72.1W 45 KT 50 MPH 36H 19/1800Z 36.5N 69.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 20/0600Z 35.6N 66.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 20/1800Z 34.4N 65.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 21/0600Z 33.0N 64.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 22/0600Z 31.0N 63.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 120H 23/0600Z...DISSIPATED $$ Forecaster Beven
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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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