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Tropical Depression Six Forecast Discussion Number 4

2019-08-27 16:34:21| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Tue Aug 27 2019 000 WTNT41 KNHC 271434 TCDAT1 Tropical Depression Six Discussion Number 4 NWS National Hurricane Center Miami FL AL062019 1100 AM EDT Tue Aug 27 2019 The cloud pattern has improved a little since yesterday, and in fact, it looks more tropical on satellite today. The depression, however, continues to be sheared with the low-level center to the north of the convection. Satellite estimates from TAFB and SAB still support an initial intensity of 30 kt. The northwesterly shear currently affecting the depression is expected to continue, and only a small increase in intensity is anticipated in the next couple of days. After that time, the shear will increase as a mid-latitude trough approaches from the west, and the circulation will be over cooler waters. This should favor the cyclone to become extratropical and then become absorbed by a larger extratropical low by the end of the forecast period. The depression has been moving very little, and it appears that during the past couple hours it has been meandering northward at about 2 kt. No significant motion is expected today with a slow north-northwestward or northward drift beginning tonight. In about a day, the southwesterly flow ahead of the approaching mid-latitude trough should steer the cyclone northeastward with increasing forward speed over the North Atlantic. The NHC track forecast is very close to the multimodel consensus TVCA and not significantly different from the previous official forecast. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 31.2N 71.2W 30 KT 35 MPH 12H 28/0000Z 31.3N 71.2W 30 KT 35 MPH 24H 28/1200Z 32.9N 71.6W 35 KT 40 MPH 36H 29/0000Z 35.0N 70.8W 35 KT 40 MPH 48H 29/1200Z 38.0N 68.3W 40 KT 45 MPH 72H 30/1200Z 44.5N 60.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 31/1200Z 50.0N 52.6W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 01/1200Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Dorian Forecast Discussion Number 12

2019-08-27 10:54:46| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Aug 27 2019 753 WTNT45 KNHC 270854 TCDAT5 Tropical Storm Dorian Discussion Number 12 NWS National Hurricane Center Miami FL AL052019 500 AM AST Tue Aug 27 2019 Dorian passed over Barbados a few hours ago and it is now very near the Windward Islands. Data from the Air Force Hurricane Hunters earlier this morning suggest that the storm has held steady in intensity with a blend of the flight level and SFMR winds supporting a wind speed of 45 kt. The Caribbean composite radar data show that Dorian remains a very compact system and that it still lacks a well-defined inner core. Dry air in the mid-levels of the atmosphere around Dorian has been causing the storm to remain in a fairly steady state during the past day or so despite relatively low wind shear conditions and warm SSTs. The models show this dry air persisting in the vicinity of the system while it tracks across the Caribbean during the next day or two, so it seems likely that Dorian will continue to only gradually intensify during that time. When Dorian nears Hispaniola in 36 to 48 hours, there will likely be some increase in wind shear and those less favorable winds aloft and the interaction with the landmasses of Puerto Rico and Hispaniola should cause considerable weakening. Once the system moves north of the Greater Antilles, the environmental conditions become more favorable for intensification, and most of the intensity guidance responds by showing an increase in winds. However, there remains considerable uncertainty for this part of the forecast because the future intensity of Dorian will be quite dependent on how much land interaction there is with the mountainous island of Hispaniola. The NHC intensity forecast lies near the upper end of the guidance in the short term, while the system is over the Caribbean Sea, but near the middle of the guidance envelope after that. The storm is moving west-northwestward at 11 kt steered by a subtropical ridge to the north. This general motion should continue for another 12 to 24 hours taking Dorian across the eastern Caribbean Sea. After that time, a slight turn to the northwest is likely when the cyclone nears the eastern portion of a cut off mid- to upper-level low and moves toward a weakness in the ridge. This should take Dorian across the Dominican Republic and the Mona Passage and over the Bahamas in the 3 to 4 day time period. A ridge is likely to rebuild to the north of Dorian when it is forecast to be over the Bahamas and that could cause it to turn slightly to the left by the end of the forecast period. The new NHC track forecast is largely unchanged while Dorian is in the Caribbean, but it has been shifted slightly to the north thereafter. 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. Key Messages: 1. Dorian is expected to bring tropical storm conditions to portions of the Lesser Antilles during the next several hours, where tropical storm watches and warnings are in effect. Rainfall of 3 to 6 inches is expected from Martinique to St. Vincent with isolated totals as high as 10 inches possible. 2. Tropical storm conditions are expected and hurricane conditions are possible in Puerto Rico on Wednesday, where a tropical storm warning and hurricane watch have been issued. Rainfall of 2 to 4 inches with maximum totals of 6 inches are possible across Puerto Rico and St. Croix. 3. Hurricane and Tropical Storm Watches have been issued for portions of the Dominican Republic. 4. While uncertainty remains high, wind and rain impacts are possible in the Bahamas and Florida later this week and this weekend. Residents in these areas should monitor the progress of Dorian and ensure that they have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 13.5N 60.7W 45 KT 50 MPH 12H 27/1800Z 14.4N 62.3W 50 KT 60 MPH 24H 28/0600Z 15.7N 64.5W 55 KT 65 MPH 36H 28/1800Z 17.0N 66.5W 60 KT 70 MPH 48H 29/0600Z 18.5N 68.2W 60 KT 70 MPH 72H 30/0600Z 21.7N 71.4W 50 KT 60 MPH 96H 31/0600Z 24.7N 75.1W 60 KT 70 MPH 120H 01/0600Z 27.1N 79.6W 60 KT 70 MPH $$ Forecaster Cangialosi

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Tropical Depression Six Forecast Discussion Number 3

2019-08-27 10:43:46| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Tue Aug 27 2019 000 WTNT41 KNHC 270843 TCDAT1 Tropical Depression Six Discussion Number 3 NWS National Hurricane Center Miami FL AL062019 500 AM EDT Tue Aug 27 2019 The satellite presentation during the past several hours shows some curved banding improvement associated with the cyclone, particularly in the southeast quadrant, however, the circulation is still poorly defined. In fact, imagery reveals multiple swirls rotating about a large circulation. No changes to the subjective satellite intensity estimates, from both TAFB and SAB, and the initial intensity is held at 30 kt for this advisory. The 25-30 kt of westerly shear, indicated by the UW-CIMSS shear product, is forecast to decrease somewhat around mid-period while the system remains over warm oceanic sea surface temperatures. This, along with some baroclinic forcing in response to an approaching mid-latitude trough from the northeast United States, should allow for the cyclone to modestly strengthening. The Florida State Cyclone Phase Evolution forecast, and the global models, including the ECMWF simulated infrared imagery, now indicate the cyclone completing an extratropical transition in 3 days, and the official forecast is adjusted accordingly. Afterward, as extratropical low quickly approaches eastern Canada, the large-scale models show the cyclone becoming absorbed by a larger baroclinic system embedded in the westerlies, and this is also indicated in the official forecast. The initial motion is estimated to be a generally southward drift, or 125/2 kt, within weak low to mid-level steering flow residing between the Bermuda high to the east and a mid-level ridge over the mid-Atlantic states. The depression is forecast to move little through today as it remains in the aforementioned weak steering current. Afterward, a mid-latitude shortwave trough is forecast to move toward the northeastern United States on Wednesday, and should induce a northeastward motion with an increase in forward speed, away from the eastern seaboard. Only a slight adjustment to the left of the previous forecast was made to align more with the reliable NOAA HCCA and TVCA consensus models. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 31.0N 71.6W 30 KT 35 MPH 12H 27/1800Z 31.4N 71.6W 30 KT 35 MPH 24H 28/0600Z 32.5N 71.7W 35 KT 40 MPH 36H 28/1800Z 34.1N 71.4W 35 KT 40 MPH 48H 29/0600Z 36.7N 69.9W 40 KT 45 MPH 72H 30/0600Z 42.9N 63.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 31/0600Z 49.8N 55.6W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 01/0600Z...DISSIPATED $$ Forecaster Roberts

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Tropical Storm Dorian Forecast Discussion Number 11

2019-08-27 04:44:15| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Aug 26 2019 000 WTNT45 KNHC 270244 TCDAT5 Tropical Storm Dorian Discussion Number 11 NWS National Hurricane Center Miami FL AL052019 1100 PM AST Mon Aug 26 2019 An Air Force Reserve Unit Hurricane Hunter aircraft has been investigating Dorian this evening. Data from the plane indicate that the storm is not quite as strong as previously estimated, and based on flight-level winds and SFMR-observed surface winds the intensity is set at 45 kt. Fixes from the aircraft show that the center of the cyclone moved just south of the southern coast of Barbados within the last couple of hours, and tropical-storm-force winds were reported over that island. There is fairly well-defined upper-level outflow over the eastern semicircle of the circulation. Although some dry mid-level air is likely to continue to affect Dorian while it moves over the northeastern Caribbean, the dynamical guidance indicates that the shear will not become very strong. Therefore it is still expected that the cyclone will become a hurricane in a couple of days. Some disruption of the system will likely occur when the center moves near eastern Hispaniola. The official intensity forecast is on the high end of the model guidance and is subject to considerable uncertainty, particularly from days 3 to 5. Dorian continues to move west-northwestward, or 290/11 kt, while being steered by the flow on the south side of the subtropical ridge. In a day or two, the tropical cyclone is expected to turn northwestward due to a weakness in the ridge. The ridge is expected to build somewhat later in the forecast period, which should cause Dorian to turn slightly to the left. The ECMWF model is near the northern side of the guidance suite and the UKMET is near the southern side. The GFS model continues to practically dissipate the system so it was unable to generate a forecast track. The official track forecast was shifted a bit to the north, but lies south of the latest dynamical model consensus. It is advisable that one not focus on small changes in the forecast track due to uncertainties. Key Messages: 1. Dorian is expected to bring tropical storm conditions to portions of the Lesser Antilles through Tuesday morning, where tropical storm watches and warnings are in effect. Rainfall of 3 to 8 inches is expected from Martinique to St. Vincent, including Barbados, with isolated totals as high as 10 inches possible. 2. Tropical storm conditions are possible in Puerto Rico on Wednesday, where a tropical storm watch has been issued. Rainfall of 2 to 4 inches with maximum totals of 6 inches are possible across Puerto Rico and St. Croix. 3. Watches will likely be issued for portions of Hispaniola early Tuesday, as the threat of wind and rain impacts continues to increase. 4. While uncertainty is high, wind and rain impacts are possible in the Bahamas and Florida later this week and this weekend. Residents in these areas should monitor the progress of Dorian and ensure that they have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 13.2N 59.7W 45 KT 50 MPH 12H 27/1200Z 14.0N 61.3W 50 KT 60 MPH 24H 28/0000Z 15.2N 63.5W 55 KT 65 MPH 36H 28/1200Z 16.5N 65.5W 60 KT 70 MPH 48H 29/0000Z 17.9N 67.6W 65 KT 75 MPH 72H 30/0000Z 21.0N 71.0W 50 KT 60 MPH 96H 31/0000Z 24.0N 74.8W 55 KT 65 MPH 120H 01/0000Z 26.5N 79.0W 60 KT 70 MPH $$ Forecaster Pasch

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Tropical Depression Six Forecast Discussion Number 2

2019-08-27 04:39:52| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Mon Aug 26 2019 000 WTNT41 KNHC 270239 TCDAT1 Tropical Depression Six Discussion Number 2 NWS National Hurricane Center Miami FL AL062019 1100 PM EDT Mon Aug 26 2019 The depression remains poorly organized this evening with the edge of the cyclone's deep convection displaced nearly 90 n mi southeast of the low level center due to northwesterly shear. A recent scatterometer pass indicates an initial intensity of 30 kt, with winds of 25 kt or greater being confined to the southeastern quadrant. The low level center has been drifting eastward this evening and the initial motion is 100/3 kt. The steering flow surrounding the cyclone is expected to stay weak for the next 24 hours, resulting in a slow, erratic motion. After 24 hours, a mid-latitude trough crossing the eastern United States will accelerate the system to the northeast, keeping it well to the east of the United States coast. The latest forecast is similar to the previous one, and near the corrected consensus HCCA. The wind shear over the depression is forecast to decrease somewhat over the next 48 hours while the system remains over warm waters. This should allow for the depression to intensify into a tropical storm during that time. After 48 hours, strong upper level southwesterly winds ahead of the approaching mid-latitude trough should initiate a gradual extratropical transition of the cyclone. After 96 hours, the cyclone is expected to be absorbed by a larger system embedded in the westerlies. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 31.5N 72.2W 30 KT 35 MPH 12H 27/1200Z 31.6N 72.0W 30 KT 35 MPH 24H 28/0000Z 32.1N 71.9W 35 KT 40 MPH 36H 28/1200Z 33.4N 71.7W 35 KT 40 MPH 48H 29/0000Z 35.5N 70.7W 40 KT 45 MPH 72H 30/0000Z 41.3N 65.1W 40 KT 45 MPH 96H 31/0000Z 48.1N 57.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 01/0000Z...DISSIPATED $$ Forecaster Latto/Pasch

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