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Tropical Storm Dorian Forecast Discussion Number 15
2019-08-28 04:50:58| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Aug 27 2019 000 WTNT45 KNHC 280250 TCDAT5 Tropical Storm Dorian Discussion Number 15 NWS National Hurricane Center Miami FL AL052019 1100 PM AST Tue Aug 27 2019 Reports from an Air Force Hurricane Hunter aircraft indicate that Dorian is yet to strengthen, and the initial intensity remains near 45 kt. The storm's cloud pattern remains rather ragged-looking with no clear convective banding features. Since the storm has strong upper-level outflow over the western semicircle of the circulation and vertical shear should remain low for the next day or two, strengthening is still forecast before Dorian reaches Puerto Rico on Wednesday. Some weakening is likely by 24 hours due to the interaction of the circulation with Puerto Rico. The intensity forecast in 3-5 days remains problematic because of a significant spread in the model guidance and some run-to-run inconsistencies. The official intensity forecast has been increased in comparison to the previous ones. However, it is now near the low end of the numerical guidance suite. Dorian has turned toward the northwest, and the initial motion estimate is 310/11 kt. Over the next couple of days, the cyclone will be headed toward a weakness in the subtropical ridge. In 3-4 days, the global models show the ridge rebuilding somewhat over the western Atlantic. This scenario should cause Dorian to turn toward the left later in the forecast period. The official forecast has been shifted to the north of the previous one. This is in close agreement with the ECMWF model track, but south and southwest of the latest simple and corrected consensus predictions. Key Messages: 1. Tropical storm conditions are expected in the U.S. and British Virgin Islands and Puerto Rico on Wednesday, and are possible in portions of the Dominican Republic Wednesday night and Thursday. Hurricane conditions are possible in Puerto Rico on Wednesday. 2. Heavy rainfall over portions of Puerto Rico and the Dominican Republic could produce flash flooding during the next few days. Heavy rains are expected to occur over portions of the Bahamas and Florida later this week and into early next week. 3. The threat of tropical storm or hurricane conditions, along with storm surge, in the Bahamas and along portions of the Florida east coast have increased. Residents in these areas should monitor the progress of Dorian and ensure that they have their hurricane plan in place. 4. Uncertainty in the intensity forecast later this week remains higher than usual due a large spread in model guidance. storm. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 16.0N 63.0W 45 KT 50 MPH 12H 28/1200Z 17.0N 64.5W 55 KT 65 MPH 24H 29/0000Z 18.5N 66.5W 45 KT 50 MPH...INLAND 36H 29/1200Z 20.3N 68.1W 50 KT 60 MPH 48H 30/0000Z 22.1N 69.6W 55 KT 65 MPH 72H 31/0000Z 25.3N 72.7W 65 KT 75 MPH 96H 01/0000Z 27.4N 76.8W 70 KT 80 MPH 120H 02/0000Z 28.8N 81.0W 65 KT 75 MPH...INLAND $$ Forecaster Pasch
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Tropical Storm Erin Forecast Discussion Number 6
2019-08-28 04:39:37| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Tue Aug 27 2019 000 WTNT41 KNHC 280239 TCDAT1 Tropical Storm Erin Discussion Number 6 NWS National Hurricane Center Miami FL AL062019 1100 PM EDT Tue Aug 27 2019 Over the past several hours, the deep convection associated with the cyclone has been developing progressively closer to the center of circulation. And, at the time of this advisory the convection is now covering a portion of the previously exposed low-level center. A late morning scatterometer pass showed winds just over 30 kt over the eastern semicircle of the cyclone. Since that time, the improved convective pattern has resulted in an increase in the subjective satellite intensity estimate from TAFB, indicating an initial intensity of 35 kt. Erin is still undergoing northerly shear, but possibly a little less now than it had been battling for the past couple of days. Little change in environmental conditions are expected over the next 36 hours, so some slight strengthening could occur during that time. After 24 hours, Erin will begin to interact with an approaching mid-latitude trough over the northeastern United States. This should cause the storm to gradually acquire extratropical characteristics, and by 48 hours Erin is expected to have completed extratropical transition. Erin continues to meander, with an initial motion of 270/3 kt. The approaching mid-latitude trough should begin to induce a northward motion of Erin tonight and then accelerate the storm to the northeast on Wednesday and Wednesday night. Model guidance is in good agreement on this scenario and the official forecast is close to the previous one, and near the corrected consensus HCCA. On this track, Erin will remain well offshore of the United States coast. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 31.9N 72.1W 35 KT 40 MPH 12H 28/1200Z 33.1N 72.4W 40 KT 45 MPH 24H 29/0000Z 36.0N 71.6W 40 KT 45 MPH 36H 29/1200Z 39.4N 68.9W 40 KT 45 MPH 48H 30/0000Z 43.7N 65.1W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 31/0000Z...DISSIPATED $$ Forecaster Latto/Pasch
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Tropical Storm Dorian Forecast Discussion Number 14
2019-08-27 23:00:25| National Hurricane Center (Atlantic)
Issued at 500 PM AST Tue Aug 27 2019 000 WTNT45 KNHC 272100 TCDAT5 Tropical Storm Dorian Discussion Number 14 NWS National Hurricane Center Miami FL AL052019 500 PM AST Tue Aug 27 2019 Dorian's convective pattern has continued to fluctuate this afternoon due to some interaction with the Windward and Leeward Islands, but mainly due to intrusions of very dry mid-level air. A 10-mile wide eye feature developed in Martinique and Guadeloupe radar data between 1500-1600 UTC and again between 1700-1800 UTC. But this feature had been short-lived due to erosion of the inner-core convection caused by dry air entrainment, although a recent burst of deep convection has developed near and over the low-level center. Dorian's upper-level outflow has continued to expand and is very symmetrical. The initial intensity has been maintained at 45 kt based on earlier aircraft flight-level and SFMR surface wind data. Despite the center redeveloping farther north, radar and recon fixes indicate that the motion remains west-northwestward or 300/11 kt. Due to the more northward initial position, the new forecast track was shifted 30-60 n mi northeast of the previous one track through 96 hours. The global models are in good agreement on Dorian moving west-northwestward tonight and then turning northwestward on Wednesday, bringing the cyclone's center near or over the central or western portions of Puerto Rico. After clearing the island by early Thursday, Dorian is forecast to move cyclonically around the eastern portion of a southwestward-moving mid/upper-level low on days 3-5. The evolution of the upper-low and how strong the mid-level ridge to the north builds in behind the low and across the southeastern U.S. will determine when and how sharp Dorian's turn back the west-northwest will occur. The new NHC track is close to a blend consensus models TVCN, HCCA, and FSSE, and brings Dorian near the east-central Florida coast in 120 hours. Users are reminded not to focus on the details of the extended track forecast as the average 5-day track error is around 200 miles. Dry air should continue to plague Dorian for the next 24 hours or so, resulting in only slow strengthening. Land interaction with Puerto Rico should significantly weaken the small cyclone, thus the intensities were lowered at 36 and 48 hours. On days 3-5, the models continue to indicate that the upper-level flow pattern and shear conditions should favor strengthening, especially since Dorian will be moving over SSTs greater than 29 deg C and into a moist mid-level environment. The dynamical models such as the GFS, UKMET, and ECMWF are now showing more strengthening than previous runs, but still remain well below the statistical SHIPS and LGEM intensity models, which bring Dorian to category 1 or 2 strength by day 5. The official intensity forecast remains a compromise between the these two extremes, and is close to the HCCA and FSSE consensus models. Given the large spread in the guidance, there remains lower-than- normal confidence in the intensity forecast, especially on days 4 and 5. Key Messages: 1. Tropical storm conditions are expected in the U.S. Virgin Islands and Puerto Rico on Wednesday and in portions of the Dominican Republic Wednesday night and Thursday. Hurricane conditions are possible in Puerto Rico and portions of the Dominican Republic. 2. Heavy rainfall over portions of Puerto Rico and the Dominican Republic could produce flash flooding during the next few days. Heavy rains are expected to occur over portions of the Bahamas and Florida later this week and into early next week. 3. The threat of tropical storm or hurricane conditions, along with storm surge, in the Bahamas and along portions of the Florida east coast have increased. Residents in these areas should monitor the progress of Dorian and ensure that they have their hurricane plan in place. 4. Uncertainty in the intensity forecast later this week remains higher than usual due to the potential for Dorian's interaction with Puerto Rico and Hispaniola to weaken the storm. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 15.3N 62.5W 45 KT 50 MPH 12H 28/0600Z 16.2N 64.1W 50 KT 60 MPH 24H 28/1800Z 17.6N 66.2W 55 KT 65 MPH 36H 29/0600Z 19.1N 67.8W 40 KT 45 MPH 48H 29/1800Z 20.8N 69.2W 45 KT 50 MPH 72H 30/1800Z 24.2N 72.2W 55 KT 65 MPH 96H 31/1800Z 26.7N 76.1W 60 KT 70 MPH 120H 01/1800Z 28.2N 80.6W 60 KT 70 MPH...NEAR THE FLORIDA COAST $$ Forecaster Stewart
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Tropical Depression Six Forecast Discussion Number 5
2019-08-27 22:34:56| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Tue Aug 27 2019 000 WTNT41 KNHC 272034 TCDAT1 Tropical Depression Six Discussion Number 5 NWS National Hurricane Center Miami FL AL062019 500 PM EDT Tue Aug 27 2019 After a brief period when the center was near the edge of the convection this morning, once again the northwesterly shear disrupted the cloud pattern, and the low-level center has become detached from the main thunderstorm activity. The Dvorak estimates have not changed and still support an initial intensity of 30 kt. Earlier ASCAT data also indicated some vectors of 30 kt in the southeast quadrant. Since the shear is not forecast to abate, only a small increase in intensity is forecast during the next 24 to 36 hours. After that time, the cyclone will be moving over cooler waters and should become extratropical while becoming absorbed by a larger trough. The depression meandered all day, but it has now been moving slowly toward the north-northwest or 345 degrees at 6 knots. This motion is highly uncertain because it includes the back and forth shifting of the center from the edge of the convection during the past several hours. The southwesterly flow ahead of the approaching mid-latitude trough should steer the cyclone northward and then northeastward with increasing forward speed over the North Atlantic. The NHC track forecast has been adjusted a little bit to the north in this advisory following the northward shift of the multimodel consensus TVCA and HCCA. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 31.8N 71.8W 30 KT 35 MPH 12H 28/0600Z 32.7N 72.1W 30 KT 35 MPH 24H 28/1800Z 35.0N 72.2W 35 KT 40 MPH 36H 29/0600Z 38.0N 70.5W 35 KT 40 MPH 48H 29/1800Z 41.5N 67.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 72H 30/1800Z...DISSIPATED $$ Forecaster Avila
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Tropical Storm Dorian Forecast Discussion Number 13
2019-08-27 17:13:22| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Tue Aug 27 2019 000 WTNT45 KNHC 271512 CCA TCDAT5 Tropical Storm Dorian Discussion Number 13...Corrected NWS National Hurricane Center Miami FL AL052019 1100 AM AST Tue Aug 27 2019 Corrected southeastward to southwestward motion in third paragraph Dorian moved directly across the center of St. Lucia around 1000 UTC, which resulted in a significant disruption of the small inner-core wind field. An Air Force Reserve reconnaissance aircraft had difficulty identifying a clear-cut center and radar data from Martinique indicates that the mid-level circulation has also been disrupted somewhat. Having said that, the overall appearance of the cyclone in both satellite and radar imagery has improved since this time yesterday, although a pronounced dry slot is now evident in the southeastern quadrant of the circulation. The initial intensity of 45 kt is being maintained based on aircraft flight-level and SFMR surface wind data. The initial motion remains west-northwestward or 295/11 kt. There is still no significant change to the previous forecast track or reasoning. Although the inner-core wind field and low-level center have been disrupted, the overall circulation envelope has remained intact and is expected to move west-northwestward to northwestward for the next 36-48 hours toward a break in the subtropical ridge located well north of Dorian. The mid- to upper-level low currently located east of the Bahamas that has weakened the ridge is forecast to gradually weaken while digging southwestward across the central Bahamas and toward central Cuba over the next 3-4 days, resulting in Dorian turning northwestward on day 3 before turning back toward the west-northwest on days 4 and 5. How quickly the west-northwestward turn occurs will depend heavily on the evolution of the upper-low. For now, the previous forecast track remains unchanged other than to push out the track a little northeastward at 48 and 72 hours. The NHC model guidance remains tightly packed and in good agreement on this scenario, and the new forecast track lies very close to an average of the various consensus track models. Users are reminded not to focus on the details of the extended track forecast as the average 5-day track error is around 200 miles. Dry air continues to plague Dorian, and interaction with the mountainous terrain of St. Lucia will likely hinder significant development in the short term. However, the models continue to indicate that the upper-level flow pattern and shear conditions are expected to remain favorable for strengthening throughout the forecast period, so it is uncertain why the dynamical models are not showing more development and strengthening when compared to the more robust statistical SHIPS intensity models, especially at days 4 and 5 when Dorian will be moving over SSTs greater than 29 deg C and into a fairly moist environment. For now, the official intensity forecast remains basically midway between the stronger SHIPS model and the much weaker global and regional models. Given the large spread in the guidance, there is lower than normal confidence in the intensity forecast, especially on days 4 an 5. Key Messages: 1. Tropical storm conditions will continue in portions of the Lesser Antilles during the next several hours. Tropical storm conditions are expected and hurricane conditions are possible in Puerto Rico on Wednesday and in portions of the Dominican Republic Wednesday night and Thursday. 2. Heavy rainfall over portions of the Lesser Antilles, Puerto Rico, and the Dominican Republic could produce flash flooding during the next few days. 3. The threat of winds and heavy rains later this week into this weekend in the Turks and Caicos, the Bahamas, and Florida is increasing. Residents in these areas should monitor the progress of Dorian and ensure that they have their hurricane plan in place. 4. Uncertainty in the intensity forecast later this week remains higher than usual due Dorian's potential interaction with Hispaniola and Puerto Rico. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 14.2N 61.8W 45 KT 50 MPH 12H 28/0000Z 15.2N 63.4W 50 KT 60 MPH 24H 28/1200Z 16.5N 65.5W 55 KT 65 MPH 36H 29/0000Z 17.9N 67.4W 60 KT 70 MPH 48H 29/1200Z 19.5N 69.0W 60 KT 70 MPH 72H 30/1200Z 22.8N 72.0W 55 KT 65 MPH 96H 31/1200Z 25.6N 76.0W 60 KT 70 MPH 120H 01/1200Z 27.8N 80.4W 60 KT 70 MPH $$ Forecaster Stewart
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