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Tropical Storm Dorian Forecast Discussion Number 10
2019-08-26 22:55:11| National Hurricane Center (Atlantic)
Issued at 500 PM AST Mon Aug 26 2019 000 WTNT45 KNHC 262055 TCDAT5 Tropical Storm Dorian Discussion Number 10 NWS National Hurricane Center Miami FL AL052019 500 PM AST Mon Aug 26 2019 Dorian's convective pattern has waxed and waned this afternoon due to intrusions of dry mid-level air while the upper-level outflow pattern has continued to expand and become more symmetrical. Although the inner-core convection has decreased recently, a recent burst of strong convection with cloud tops colder than -80C has redeveloped just north of the low-level center. The initial intensity remains at 50 kt based on a an average of satellite intensity estimates ranging from 45 kt to 61 kt from TAFB, SAB, and UW-CIMSS SATCON and ADT. An Air Force Reserve reconnaissance aircraft is scheduled to investigate Dorian by 0000 UTC this evening, and will provide a better estimate of the cyclone's intensity. The initial motion is west-northwestward or 290/12 kt. There is no significant change to the previous forecast track or reasoning. The latest NHC model guidance remains in very agreement that Dorian will move west-northwestward across the central Lesser Antilles tonight and into the northeastern Caribbean Sea on Tuesday as the cyclone moves around the edge of the Bermuda-Azores ridge located well to the north. On Wednesday, Dorian should turn northwestward into a small weakness in the ridge, allowing the tropical cyclone to pass near or between western Puerto Rico and the eastern Dominican Republic. By late Thursday and Friday, the ridge is forecast to build back in as an upper-level trough lifts out to the north, causing Dorian to turn back toward the west-northwest in the vicinity of the central Bahamas. The new official forecast track is just an extension of the previous one since the latest model guidance, especially the consensus models, are tightly packed around the previous track forecast. The intensity forecast remains something of an enigma. The majority of the environmental conditions support at least steady strengthening, with the main hindrance being the very dry mid-level air surrounding the cyclone and occasionally being entrained into Dorian's inner-core region. The small but robust circulation should continue mix out the brief dry air intrusions, but when an eyewall will form is still uncertain. Given that Dorian will be moving into the convective maximum period later tonight, the intensity forecast still calls for Dorian be near hurricane strength when it passes through the Windward Islands. Interaction with Hispaniola and possibly Puerto Rico should result in some weakening in 72-96 hours, followed by restrengthening on days 4 and 5 when Dorian will be moving over the very warm waters in the Bahamas in low shear conditions. Most of the global models along with the statistical- dynamical SHIPS and LGEM intensity models are now showing pronounced strengthening while Dorian is moving near or through the Bahamas, so the official forecast shows a significant change to the previous one at 96 and 120 hours. However, confidence in the intensity forecast at days 4 and 5 is very low given the uncertainty about how much of Dorian's core will interact with Hispaniola. Key Messages: 1. Dorian is expected to bring tropical storm conditions to portions of the Lesser Antilles tonight and Tuesday, where tropical storm watches and warnings are in effect. Hurricane conditions are possible in St. Lucia, where a Hurricane Watch is 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 tonight or 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 26/2100Z 12.7N 58.8W 50 KT 60 MPH 12H 27/0600Z 13.4N 60.5W 55 KT 65 MPH 24H 27/1800Z 14.5N 62.6W 60 KT 70 MPH 36H 28/0600Z 15.7N 64.6W 65 KT 75 MPH 48H 28/1800Z 17.1N 66.7W 70 KT 80 MPH 72H 29/1800Z 20.1N 70.2W 50 KT 60 MPH 96H 30/1800Z 23.0N 73.8W 55 KT 65 MPH 120H 31/1800Z 25.5N 78.0W 60 KT 70 MPH $$ Forecaster Stewart
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Tropical Depression Six Forecast Discussion Number 1
2019-08-26 22:38:42| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon Aug 26 2019 000 WTNT41 KNHC 262038 TCDAT1 Tropical Depression Six Discussion Number 1 NWS National Hurricane Center Miami FL AL062019 500 PM EDT Mon Aug 26 2019 The circulation associated with the area of low pressure that has been tracked across the western Atlantic the past several days has become better defined during the past 24 hours. The associated convection, which is located well to the southeast of the low-level center due to shear, has also become more persistent and organized into a band today. As a result, advisories are being initiated on a tropical depression. The initial wind speed has been set at 30 kt, based on earlier ASCAT data. There were a few 35-kt vectors in the ASCAT-A overpass but those data appeared to be rain-inflated. The depression is currently located over warm water but within an environment of moderate westerly shear, which is likely to continue during the next day or so. Although some slight strengthening is forecast, the shear is likely to prohibit significant deepening during that time. After 36 h, the shear is forecast to decrease while the system moves northeastward and some modest strengthening is anticipated. Later in the period, an approaching mid-latitude trough may also help to strengthen the cyclone due to baroclinic processes, and the system is forecast to become extratropical in 3 to 4 days, and should be absorbed by a larger extratropical cyclone by day 5. The initial motion estimate is a somewhat uncertain 080/2 kt. The depression is forecast to drift eastward or northeastward during the next day or so as it remains in an area of weak steering flow between a couple of mid-level anticyclones. As the aforementioned mid-latitude trough approaches the northeastern United States on Wednesday, it should cause the cyclone to accelerate northeastward well east of the east coast of the United States. The track guidance is in relatively good agreement, but there are some differences in how fast it will be ejected northeastward. The NHC track forecast leans toward the slower ECMWF solution during the first day or so, then closer to the consensus aids later in the period. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 31.7N 72.5W 30 KT 35 MPH 12H 27/0600Z 31.8N 72.0W 35 KT 40 MPH 24H 27/1800Z 32.1N 71.9W 35 KT 40 MPH 36H 28/0600Z 32.9N 71.9W 35 KT 40 MPH 48H 28/1800Z 34.6N 71.5W 40 KT 45 MPH 72H 29/1800Z 40.3N 66.8W 45 KT 50 MPH 96H 30/1800Z 47.0N 60.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 31/1800Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Dorian Forecast Discussion Number 9
2019-08-26 17:00:10| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Aug 26 2019 000 WTNT45 KNHC 261500 TCDAT5 Tropical Storm Dorian Discussion Number 9 NWS National Hurricane Center Miami FL AL052019 1100 AM AST Mon Aug 26 2019 Satellite imagery indicates that Dorian's convective and outflow pattern have continued to improve, with a narrow poleward outflow channel now apparent in water vapor images. Passive microwave imagery has shown a persistent low-level eye-like feature along with an intermittent mid-level eyewall forming that quickly erodes due to mid-level dry air entrainment. The initial intensity of 50 kt is based on a blend of satellite intensity estimates ranging from 45 kt to 56 kt from TAFB, SAB, and UW-CIMSS ADT and SATCON. The initial motion is now west-northwestward or 285/12 kt. Dorian is expected to continue moving west-northwestward today through Tuesday night as the cyclone moves around the southwestern periphery of a deep-layer subtropical ridge situated to its north. On Wednesday, Dorian is forecast to turn northwestward toward a weakness in the ridge, which could allow the cyclone to pass near or between western Puerto Rico and the eastern Dominican Republic. By late Thursday and Friday, all of the model guidance indicates that the ridge will build back as an upper-level trough/low weakens and lifts out to the north, which should result in Dorian turning back toward the west-northwest in the vicinity of the Bahamas. The new NHC track forecast has been nudged slightly to the right or north of the previous one and lies close to the tightly clustered consensus models HCCA, FSSE, TVCN, and TVCX. The intensity forecast is less straight-forward than the track forecast. Environmental conditions, except for the abundance of dry mid-level air surrounding and occasionally being entrained into Dorian's inner-core region, would favor at least steady strengthening due to very low vertical wind shear, SSTs of at least 29C, and the small overall circulation and inner-core wind field. The recent development of a poleward outflow channel and possible development of an equatorward channel would also support strengthening. However, until Dorian closes off a solid eyewall, only slow strengthening is likely. Anticipating when an eye will form is challenging, but Dorian could be a hurricane by the time it reaches the Windward Islands. The intensity forecast has been adjusted upward form the previous advisory, but is not as high as the statistical-dynamical SHIPS and LGEM intensity models. Interaction with Hispaniola and possibly Puerto Rico should result in some weakening in 72-96 hours, followed by restrengthening on day 5 when Dorian will be moving over the very warm waters in the Bahamas in low shear conditions. Given the unknown degree of interaction with Hispaniola, the intensity forecast at days 4 and 5 is of very low confidence. Key Messages: 1. Dorian is expected to bring tropical storm conditions to portions of the Lesser Antilles tonight and Tuesday, where tropical storm watches and warnings are in effect. Hurricane conditions are also possible in portions of the Windward Islands, and a hurricane watch has been issued for St. Lucia. Residents in these areas should refer to advice from local government officials and products from their local meteorological service for additional information. 2. Dorian is expected to produce 3 to 8 inches of rainfall from Martinique to St. Vincent, including Barbados, with isolated totals as high as 10 inches in portions of the northern Windward Islands. 3. The risk of direct impacts from wind and rainfall has increased for Puerto Rico and Hispaniola. Interests in those areas should monitor the progress of Dorian and tropical storm or hurricane watches will likely be required later today. 4. Any potential impacts from Dorian in the Bahamas and Florida later this week are highly uncertain, given the potential for the system to interact with the high terrain of Hispaniola. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 12.3N 57.7W 50 KT 60 MPH 12H 27/0000Z 12.9N 59.4W 55 KT 65 MPH 24H 27/1200Z 13.9N 61.4W 60 KT 70 MPH 36H 28/0000Z 15.1N 63.5W 65 KT 75 MPH 48H 28/1200Z 16.4N 65.6W 70 KT 80 MPH 72H 29/1200Z 19.2N 69.3W 70 KT 80 MPH...NERN HISPANIOLA 96H 30/1200Z 22.0N 72.6W 40 KT 45 MPH 120H 31/1200Z 24.8N 76.5W 45 KT 50 MPH $$ Forecaster Stewart
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Tropical Storm Dorian Forecast Discussion Number 8
2019-08-26 10:49:38| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Aug 26 2019 000 WTNT45 KNHC 260849 TCDAT5 Tropical Storm Dorian Discussion Number 8 NWS National Hurricane Center Miami FL AL052019 500 AM AST Mon Aug 26 2019 Satellite images indicate that deep convection associated with Dorian continues to fluctuate curtailing significant strengthening likely due to intrusions of dry air. The overall trend, however, suggests that Dorian is gradually getting better organized with its cloud pattern consisting of a compact central dense overcast and some broken outer bands. The initial intensity is nudged up to 50 kt based on a blend of the satellite intensity estimates. Dorian remains a small storm with its tropical-storm-force winds estimated to extend no more than 40 n mi from the center. During the next couple of days, as Dorian moves through the Windward Islands and across the eastern Caribbean, slow strengthening seems likely due to low wind shear conditions and high SSTs. However, the surrounding dry air around the cyclone should continue to limit the rate of intensification. When Dorian approaches Hispaniola in about 3 days, the models show an increase in shear and those stronger environmental winds and the potential interaction with the rugged terrain of Hispaniola suggest that significant weakening is likely. The NHC intensity forecast remains between the dynamical models that show little or no strengthening and the statistical DSHP and LGEM that show significant intensification. It should be noted that the GFS and ECMWF have been very consistent in showing Dorian dissipating over the Caribbean Sea. Due to the wide range of the model solutions, the NHC intensity forecast remains of low confidence. It should be noted that compact tropical cyclones like Dorian are often challenging to predict. Dorian is moving westward at 12 kt steered by a subtropical ridge to its north. The storm should turn west-northwestward today and then northwestward on Wednesday when the cyclone gets closer to the eastern end of the mid- to upper-level low. The track models have shifted slightly to the right or north this cycle, and the NHC track forecast has been nudged in that direction. Key Messages: 1. Dorian is expected to bring tropical storm conditions to portions of the Lesser Antilles, where tropical storm watches and warnings are in effect. Residents in these areas should refer to advice from local government officials and products from their local meteorological service for additional information. 2. Dorian is expected to produce 2 to 4 inches of rain in Barbados, the Windward Islands, and Dominica, with isolated amounts as high as 6 inches. 3. While it is too soon to determine the specific time or magnitude of possible direct impacts in Puerto Rico, the Virgin Islands, or Hispaniola, interests in those areas should monitor the progress of Dorian and watches could be required later today. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 11.9N 56.4W 50 KT 60 MPH 12H 26/1800Z 12.4N 58.2W 50 KT 60 MPH 24H 27/0600Z 13.2N 60.3W 55 KT 65 MPH 36H 27/1800Z 14.4N 62.4W 55 KT 65 MPH 48H 28/0600Z 15.5N 64.5W 60 KT 70 MPH 72H 29/0600Z 18.0N 68.4W 65 KT 75 MPH 96H 30/0600Z 20.8N 71.6W 30 KT 35 MPH 120H 31/0600Z 23.0N 75.0W 30 KT 35 MPH $$ Forecaster Cangialosi
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Tropical Storm Dorian Forecast Discussion Number 7
2019-08-26 04:37:35| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Aug 25 2019 000 WTNT45 KNHC 260237 TCDAT5 Tropical Storm Dorian Discussion Number 7 NWS National Hurricane Center Miami FL AL052019 1100 PM AST Sun Aug 25 2019 Dorian's cloud pattern hasn't changed much since this afternoon, with deep convection oscillating up and down. There are few banding features evident, and the upper-level outflow is somewhat restricted over the eastern semicircle of the circulation. The intensity estimate remains at 45 kt and is in agreement with a recent Dvorak estimate from TAFB. The intensity forecast for this storm is a challenge, since the numerical guidance depicts a wide range of possibilities. The GFS and ECMWF global models dissipate Dorian over the Caribbean in about 4 days, probably due to the hostile environment associated with an upper-level low near Hispaniola. Another unfavorable factor could be dry air that is also forecast by the global models over the Caribbean. On the other hand, the statistical/dynamical models DSHIPS and LGEM do not weaken the system until it interacts with the land mass of Hispaniola. The official forecast is close to the intensity model consensus, IVCN, but it should be noted that there is greater than usual uncertainty associated with this forecast. The motion continues to be slightly north of due west or 280/12. Dorian is moving along the southern side of the subtropical ridge. The track models are in good agreement that the cyclone will gradually turn toward the west-northwest on Monday. A slight weakness in the ridge near 70W longitude in a couple of days should induce a gradual turn to the northwest later in the forecast period. The official track forecast is close to the corrected consensus, HCCA prediction and is also very close to the previous NHC track. Key Messages: 1. Dorian is expected to bring tropical storm conditions to portions of the Lesser Antilles, where tropical storm watches and warnings are in effect. Residents in these areas should refer to advice from local government officials and products from their local meteorological service for additional information. 2. Dorian is expected to produce 2 to 4 inches of rainfall across portions of the Lesser Antilles, with isolated amounts as high as 6 inches. 3. While it is too soon to determine the specific time or magnitude of possible direct impacts in Puerto Rico, the Virgin Islands, or Hispaniola interests in those areas should monitor the progress of Dorian. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 11.7N 55.3W 45 KT 50 MPH 12H 26/1200Z 12.1N 57.0W 50 KT 60 MPH 24H 27/0000Z 12.8N 59.3W 55 KT 65 MPH 36H 27/1200Z 13.7N 61.5W 55 KT 65 MPH 48H 28/0000Z 14.8N 63.6W 60 KT 70 MPH 72H 29/0000Z 17.2N 67.6W 65 KT 75 MPH 96H 30/0000Z 19.5N 71.0W 40 KT 45 MPH...INLAND 120H 31/0000Z 21.5N 74.0W 25 KT 30 MPH...OVER WATER $$ Forecaster Pasch/Latto
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