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Tropical Storm Gabrielle Forecast Discussion Number 27

2019-09-10 04:33:25| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Sep 09 2019 000 WTNT43 KNHC 100233 TCDAT3 Tropical Storm Gabrielle Discussion Number 27 NWS National Hurricane Center Miami FL AL082019 1100 PM AST Mon Sep 09 2019 Gabrielle's convection has waned considerably since the previous advisory, and the cloud pattern now has a disheveled appearance that is becoming more reminiscent of an extratropical low pressure system. However, a recent 2246Z ASCAT-A scatterometer pass indicated that the tropical storm has maintained a very robust surface wind field, with peak winds still at 45 kt and a radius of maximum winds of 45-50 nmi. The initial motion estimate is 055/21 kt, based primarily on passive microwave and scatterometer satellite fixes. Gabrielle is now well embedded in the high-latitude westerlies, and an additional increase in forward speed toward the northeast or east-northeast is expected over the next 2 days. By 72 hours, Gabrielle is forecast to dissipate near the northern British Isles. Gabrielle is currently located over sub-25 deg C sea-surface temperatures and within a strong vertical wind shear regime of near 30 kt. With much colder water and stronger southwesterly shear ahead of the cyclone, extratropical transition now appears likely to occur within the next 12 hours. The intensity forecast is similar to the previous advisory, and is a blend of the statistical SHIPS intensity models, and the GFS and ECMWF dynamical model wind fields. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 42.1N 43.1W 45 KT 50 MPH 12H 10/1200Z 44.0N 39.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 11/0000Z 46.6N 34.6W 40 KT 45 MPH...POST-TROP/EXTRATROP 36H 11/1200Z 50.1N 27.1W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 12/0000Z 54.0N 16.6W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 13/0000Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Gabrielle Forecast Discussion Number 26

2019-09-09 22:33:53| National Hurricane Center (Atlantic)

Issued at 500 PM AST Mon Sep 09 2019 000 WTNT43 KNHC 092033 TCDAT3 Tropical Storm Gabrielle Discussion Number 26 NWS National Hurricane Center Miami FL AL082019 Issued by the NWS Weather Prediction Center College Park MD 500 PM AST Mon Sep 09 2019 Satellite imagery continues to show symmetric convection around the center of Gabrielle despite some gradual warming in the cloud tops seen in the latest GOES infrared imagery. The initial wind speed was maintained at 45 kt, near the TAFB satellite estimate and a little above the SAB estimate. Gabrielle remains on a northeastward motion and is moving a bit faster than the previous advisory, or 040/18 kt. The system is expected to further increase in forward speed in a similar direction over the next couple of days due to strengthening southwesterly flow near a mid-latitude trough. Only a slight northward adjustment was made to the prior NHC forecast since, overall, model guidance remains tightly clustered with the track of Gabrielle. The storm has less than a day over marginally warm waters before it crosses the north wall of the Gulf Stream and into much colder waters. Gabrielle should transition into an extratropical low on Tuesday night as a result of an increase in shear and low-level baroclinicity from an approaching cold front. The intensity forecast is essentially unchanged from the previous forecast and continues to use a blend of the GFS and ECMWF model wind fields. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 40.7N 45.4W 45 KT 50 MPH 12H 10/0600Z 42.6N 42.4W 45 KT 50 MPH 24H 10/1800Z 45.1N 37.7W 40 KT 45 MPH 36H 11/0600Z 48.2N 31.4W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 11/1800Z 52.0N 22.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 12/1800Z...DISSIPATED $$ Forecaster Taylor/Blake

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Tropical Storm Gabrielle Forecast Discussion Number 25

2019-09-09 16:59:45| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Mon Sep 09 2019 ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM Tropical Storm Gabrielle Discussion Number 25 NWS National Hurricane Center Miami FL AL082019 Issued by the NWS Weather Prediction Center College Park MD 1100 AM AST Mon Sep 09 2019 Satellite images indicate that deep convection has increased overnight and become more symmetric around the center of Gabrielle. Still, ASCAT data show maximum winds of only about 40 kt, suggestive that this convective burst hasn't changed the intensity much. The initial wind speed is set to 45 kt, near the TAFB satellite estimate and a little above the ASCAT data to account for undersampling. Gabrielle has turned northeastward and picked up some speed. The system is expected to move at an increasing pace in a similar direction over the next few days as it is picked up by a mid-latitude trough. Model guidance is tightly clustered around the previous NHC prediction, and no significant changes were made to the prior NHC track forecast. The storm has about a day over marginally warm waters before it crosses the north wall of the Gulf Stream into much colder waters. Gabrielle is forecast to transition into an extratropical low by Tuesday due to an increase in shear and baroclinicity from an approaching cold front. The intensity forecast was reduced slightly from the previous one and is in close agreement with a blend of the GFS/ECMWF wind speed forecasts, which should best handle this extratropical transition scenario. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 39.0N 47.3W 45 KT 50 MPH 12H 10/0000Z 40.9N 44.7W 45 KT 50 MPH 24H 10/1200Z 43.4N 40.2W 45 KT 50 MPH 36H 11/0000Z 46.4N 34.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 11/1200Z 50.1N 26.9W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 12/1200Z 57.5N 5.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 13/1200Z...DISSIPATED $$ Forecaster Taylor/Blake NNNN

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Tropical Storm Gabrielle Forecast Discussion Number 24

2019-09-09 10:34:45| National Hurricane Center (Atlantic)

Issued at 500 AM AST Mon Sep 09 2019 000 WTNT43 KNHC 090834 TCDAT3 Tropical Storm Gabrielle Discussion Number 24 NWS National Hurricane Center Miami FL AL082019 500 AM AST Mon Sep 09 2019 Deep convection associated with Gabrielle has become somewhat less organized overnight with the center located near the northeastern portion of the coldest cloud tops. There is still banding present over the southern and southwestern portions of the circulation but it has become fragmented. Gabrielle has likely peaked in intensity, and the latest satellite estimates and earlier ASCAT data support an initial intensity of 50 kt for this advisory. Little change in intensity is expected today while Gabrielle remains over warm water and within a moderate shear environment. By tonight, decreasing SSTs and increasing southerly shear should begin to cause gradual weakening. Shortly after that time, the global models indicate Gabrielle will become embedded within a baroclinic zone and become extratropical. The extratropical low is predicted to slowly weaken and be absorbed by a larger low pressure system over the northeastern Atlantic in a little more than 3 days. Gabrielle has turned north-northeastward with an initial motion estimate of 015/14 kt. Gabrielle should turn northeastward today and begin to accelerate ahead of a broad mid-level trough approaching the central Atlantic. Once the cyclone is fully embedded within the mid-latitude westerlies, an additional acceleration toward the northeast is expected. There is good agreement among the dynamical models, and the updated NHC track forecast is similar to the previous advisory. The official forecast track remains between the TVCA and HCCA consensus models. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 37.7N 48.5W 50 KT 60 MPH 12H 09/1800Z 39.7N 46.6W 50 KT 60 MPH 24H 10/0600Z 42.2N 42.9W 50 KT 60 MPH 36H 10/1800Z 44.8N 38.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 11/0600Z 48.1N 31.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 12/0600Z 55.8N 12.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 13/0600Z...DISSIPATED $$ Forecaster Brown

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Post-Tropical Cyclone Dorian Forecast Discussion Number 64

2019-09-09 04:43:13| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Sep 08 2019 000 WTNT45 KNHC 090243 TCDAT5 Post-Tropical Cyclone Dorian Discussion Number 64 NWS National Hurricane Center Miami FL AL052019 1100 PM AST Sun Sep 08 2019 The center of Post-Tropical Cyclone Dorian is now located northeast of Newfoundland over the Labrador Sea where sea-surface temperatures are less than 10 deg C. No significant convection exists within 120 nmi of the center and, thus, Dorian has become fully extratropical. Therefore, this is the last advisory on this system. The post-tropical cyclone is now moving east-northeastward or 060/21 kt. This general motion should continue through Tuesday or until the cyclone is absorbed by a larger extratropical low. The NOAA Ocean Prediction Center (OPC) once again provided guidance on the intensity and wind radii forecasts, and initial 12-ft seas radii. The post-tropical cyclone is forecast to gradually weaken through Tuesday or until it is absorbed by a larger low. Key Messages: 1. Dorian will continue to cause some impacts across portions Atlantic Canada into early Monday morning. Storm surge impacts will gradually subside over portions of the northeastern Gulf of St. Lawrence and western Newfoundland. Tropical-storm-force wind gusts will continue over portions of southeastern Newfoundland into early Monday but should end by late Monday morning. Refer to information from the Canadian Hurricane Centre for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 52.1N 53.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 12H 09/1200Z 53.6N 48.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 10/0000Z 55.1N 41.5W 40 KT 45 MPH...POST-TROP/EXTRATROP 36H 10/1200Z 56.6N 31.6W 35 KT 40 MPH...POST-TROP/EXTRATROP 48H 11/0000Z...DISSIPATED $$ Forecaster Stewart

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