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Tropical Storm Gabrielle Forecast Discussion Number 20

2019-09-08 10:33:03| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Sep 08 2019 000 WTNT43 KNHC 080832 TCDAT3 Tropical Storm Gabrielle Discussion Number 20 NWS National Hurricane Center Miami FL AL082019 500 AM AST Sun Sep 08 2019 Gabrielle has become a little better organized overnight. The storm now has well-defined curved bands, especially to the south of the center, with some evidence of an inner core trying to form. The initial intensity is nudged upward to 50 kt, which is between the Dvorak classification from TAFB and the latest satellite consensus estimate from the CIMSS at the University of Wisconsin. Earlier ASCAT data revealed that Gabrielle is a compact storm with its tropical-storm-force winds only extending out to about 60 n mi from the center. The tropical storm is gradually turning to the right, with the initial motion estimated to be northwestward at 11 kt. The system is located near the southwestern periphery of a mid-level ridge centered near the Azores, and it should be moving around the western side of that ridge later today and tonight. This should cause Gabrielle to turn northward with some increase in forward speed during that time. An even faster northeastward motion is expected on Monday and Tuesday as Gabrielle, or its post-tropical remnants, become embedded in the mid-latitude westerlies. The track models are in fairly good agreement, and only minor adjustments were made to the previous forecast. Gabrielle could strengthen a little more today while it remains over warm water and in generally favorable atmospheric conditions. However, the combined influences of increasing southerly shear and cooler waters should end the chances of intensification on Monday. The global models are in agreement that Gabrielle should become extratropical when it merges with a cold front that is associated with Post-Tropical Cyclone Dorian in a little more than 2 days. The extratropical low is expected to gradually weaken and ultimately dissipate in 4 to 5 days. The NHC intensity forecast is largely an update of the previous one and in line with the majority of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 32.7N 48.6W 50 KT 60 MPH 12H 08/1800Z 34.3N 49.2W 55 KT 65 MPH 24H 09/0600Z 37.1N 48.5W 55 KT 65 MPH 36H 09/1800Z 40.1N 45.7W 55 KT 65 MPH 48H 10/0600Z 42.7N 41.0W 55 KT 65 MPH 72H 11/0600Z 48.1N 28.6W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 12/0600Z 56.0N 10.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 13/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Post-Tropical Cyclone Dorian Forecast Discussion Number 60

2019-09-08 04:34:02| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Sep 07 2019 000 WTNT45 KNHC 080233 TCDAT5 Post-Tropical Cyclone Dorian Discussion Number 60 NWS National Hurricane Center Miami FL AL052019 1100 PM AST Sat Sep 07 2019 The center of Post-Tropical Cyclone Dorian made landfall near Sambro Creek, Nova Scotia several hours ago. Since then, the powerful cyclone has continued to move rapidly to the north-northeast and is now just east of Prince Edward Island. The wind field has expanded considerably, and the cyclone is producing tropical-storm-force winds over an extensive area of the Canadian Maritimes. The powerful cyclone is expected to continue with a large wind field, but gradual weakening is anticipated as forecast by most of the global models. The best estimate of the initial motion is toward the north- northeast at 23 kt. Since the cyclone is embedded within the fast extratropical westerly flow, this general track with a turn to the northeast is anticipated until dissipation in about 2 days. Track guidance is in very good agreement with this motion, and the NHC forecast follows the guidance envelope. The Ocean Prediction Center (OPC) provided guidance to prepare this forecast. The National Hurricane Center will continue to issue advisories on Dorian as a post-tropical cyclone until the threat to eastern Canada has ended. Key Messages: 1. Dorian will continue to have significant impacts in portions of eastern Canada overnight and Sunday. Dangerous storm surge impacts are likely in portions of the Gulf of St. Lawrence, southwestern Newfoundland and eastern Nova Scotia. Hurricane-force winds are still occurring in Nova Scotia and are forecast to occur in Newfoundland overnight. Refer to information from the Canadian Hurricane Centre for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 46.3N 62.1W 80 KT 90 MPH...POST-TROPICAL 12H 08/1200Z 49.0N 60.0W 70 KT 80 MPH...POST-TROP/EXTRATROP 24H 09/0000Z 52.0N 54.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 36H 09/1200Z 54.5N 48.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 10/0000Z 56.0N 41.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 11/0000Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Gabrielle Forecast Discussion Number 19

2019-09-08 04:32:32| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Sep 07 2019 000 WTNT43 KNHC 080232 TCDAT3 Tropical Storm Gabrielle Discussion Number 19 NWS National Hurricane Center Miami FL AL082019 1100 PM AST Sat Sep 07 2019 Microwave data indicate that Gabrielle has a well-organized central core. However, the convection isn't very deep, perhaps because of dry air entrainment, with most of the convection in a band southeast of the center. The initial intensity is kept at 45 kt, which agrees well with an ASCAT-B pass of 40-45 kt and the latest TAFB fix. The storm is moving steadily west-northwestward around the southwestern side of a mid-level high over the eastern Atlantic. This high is forecast to slide eastward as the westerlies intensify due to flow around Gabrielle's southern flank in the far north Atlantic. Models are in very good agreement overall, but there continues to be some speed differences. The NHC forecast is on the faster side of the guidance, near the NOAA corrected-consensus guidance and the previous forecast, since the typical error in the higher latitudes is to be too slow. The low-shear area that was supposed to materialize in the subtropical Atlantic near Gabrielle this weekend did not occur, and as a result there is very little guidance suggesting that the cyclone will become a hurricane. The storm still has a day or two to strengthen over relatively warm waters before shear increases markedly, and water temperatures plummet north of the Gulf Stream. The intensity forecast is reduced about 5 kt from the previous one at 36-48 h, although still above the model consensus, and is similar thereafter. All models still show extratropical transition by 72 h and dissipation by day 5. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 32.0N 48.0W 45 KT 50 MPH 12H 08/1200Z 33.4N 49.3W 50 KT 60 MPH 24H 09/0000Z 35.8N 49.4W 55 KT 65 MPH 36H 09/1200Z 38.8N 47.6W 55 KT 65 MPH 48H 10/0000Z 41.7N 43.6W 55 KT 65 MPH 72H 11/0000Z 47.0N 31.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 12/0000Z 54.5N 13.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 13/0000Z...DISSIPATED $$ Forecaster Blake

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Post-Tropical Cyclone Dorian Forecast Discussion Number 59

2019-09-07 22:45:56| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Sep 07 2019 000 WTNT45 KNHC 072045 TCDAT5 Post-Tropical Cyclone Dorian Discussion Number 59 NWS National Hurricane Center Miami FL AL052019 500 PM AST Sat Sep 07 2019 Satellite imagery and surface observations indicate that Dorian has lost tropical cyclone characteristics and is now a hurricane-force extratropical low. The initial intensity is held at 85 kt based mainly on the earlier scatterometer data. The initial motion is 040/26. Strong mid-latitude southwesterly flow should steer Dorian across Nova Scotia and other portions of eastern Canada during the next 24-30 h. After that, the cyclone should turn east-northeastward over the far north Atlantic, with this motion continuing for the rest of the system's life. Global model guidance indicates that the post-tropical cyclone should gradually weaken as it moves across eastern Canada, and the new intensity forecast brings the winds below hurricane force by 24 h. Additional weakening should then occur until the storm is absorbed by a large extratropical low to its north. The National Hurricane Center will continue to issue advisories on Dorian as a post-tropical cyclone until the threat to eastern Canada has ended. Key Messages: 1. Although Dorian has lost tropical cyclone characteristics, it will have significant impacts in portions of eastern Canada tonight and Sunday. Dangerous storm surge impacts are likely in portions of the Gulf of St. Lawrence, southwestern Newfoundland and eastern Nova Scotia. Hurricane-force winds are also likely in Nova Scotia, Prince Edward Island and Newfoundland later today and tonight. Refer to information from the Canadian Hurricane Centre for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 43.9N 63.9W 85 KT 100 MPH...POST-TROPICAL 12H 08/0600Z 47.0N 61.1W 70 KT 80 MPH...POST-TROP/EXTRATROP 24H 08/1800Z 50.2N 56.9W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 09/0600Z 53.0N 50.9W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 09/1800Z 55.4N 43.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 10/1800Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Gabrielle Forecast Discussion Number 18

2019-09-07 22:35:28| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Sep 07 2019 000 WTNT43 KNHC 072035 TCDAT3 Tropical Storm Gabrielle Discussion Number 18 NWS National Hurricane Center Miami FL AL082019 500 PM AST Sat Sep 07 2019 Gabrielle is still a disorganized tropical cyclone. The center is definitely more apparent--after its morning re-formation--but it appears to be wobbling around within a larger oval-shaped circulation. Most of the deep convection is also displaced to the west and southwest of the center due to about 20 kt of easterly shear. The initial intensity remains 45 kt based on earlier scatterometer data. The cyclone has been rotating around the northeastern side of a mid- to upper-level low, but as this low weakens, Gabrielle is expected to recurve around the western side of a mid-tropospheric high located near the Azores. Gabrielle should then get picked up by the mid-latitude westerlies in about 48 hours, at which point it will accelerate northeastward toward the north Atlantic. The track models remain in good agreement on Gabrielle's future trajectory, but there are some speed differences, particularly between the faster GFS and slower ECMWF once the cyclone becomes extratropical. The updated NHC forecast splits the difference, lying near the various consensus models, which makes it just a little west of the previous forecast during the first 36 hours. Gabrielle has about another 36 hours over waters that are 26C or warmer, but the moderate-to-strong vertical shear currently affecting the system is likely to continue, and then increase significantly starting in 48 hours. Therefore, only modest strengthening is anticipated, and the NHC intensity forecast is now near the high end of the intensity models. All the global models indicate that Gabrielle should become an extratropical cyclone by 72 hours, and then it should dissipate by 120 hours. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 31.9N 46.5W 45 KT 50 MPH 12H 08/0600Z 32.9N 48.3W 50 KT 60 MPH 24H 08/1800Z 34.9N 49.4W 55 KT 65 MPH 36H 09/0600Z 37.7N 48.7W 60 KT 70 MPH 48H 09/1800Z 40.8N 45.6W 60 KT 70 MPH 72H 10/1800Z 46.0N 33.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 11/1800Z 52.0N 17.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 12/1800Z...DISSIPATED $$ Forecaster Berg

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