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Tropical Storm Joyce Forecast Discussion Number 10

2018-09-15 04:42:01| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 14 2018 013 WTNT45 KNHC 150241 TCDAT5 Tropical Storm Joyce Discussion Number 10 NWS National Hurricane Center Miami FL AL102018 1100 PM AST Fri Sep 14 2018 Joyce continues to look better organized on GOES-16 satellite imagery and the convective canopy has expanded. However, recent microwave data reveals that the cyclone is still tilted to the northeast due to nearly strong southwesterly wind shear. The most recent TAFB and SAB Dvorak classifications support raising the initial intensity to 45 kt. Despite the shear, most of the intensity guidance shows very slight strengthening over the next 12 to 24 hours, and the NHC intensity forecast is a little higher than the previous advisory at most forecast times. Persistent shear and decreasing SSTs along the forecast track should cause Joyce to weaken beyond that time, likely dissipating entirely shortly after 72 h. A few models, most notably the HWRF and UKMET, persist the cyclone a little beyond that, but only as a remnant low. The storm has turned east as expected, and the initial motion is now 090/5 kt. As the larger Helene begins to accelerate away, a mid-latitude trough over the central Atlantic should cause Joyce to turn northeastward and speed up. A turn back toward the east, or possibly even east-southeast is possible by the end of the forecast period as Joyce weakens and follows the northern periphery of a subtropical high over eastern Atlantic. Very little change has been made to the track forecast through 48 h, but it has been adjusted to the south at 72 h, following the latest consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 31.6N 43.6W 45 KT 50 MPH 12H 15/1200Z 32.2N 42.1W 50 KT 60 MPH 24H 16/0000Z 33.2N 39.8W 50 KT 60 MPH 36H 16/1200Z 34.4N 37.1W 45 KT 50 MPH 48H 17/0000Z 35.1N 33.6W 40 KT 45 MPH 72H 18/0000Z 34.0N 28.4W 35 KT 40 MPH 96H 19/0000Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Isaac Forecast Discussion Number 30

2018-09-15 04:39:03| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 14 2018 956 WTNT44 KNHC 150238 TCDAT4 Tropical Storm Isaac Discussion Number 30 NWS National Hurricane Center Miami FL AL092018 1100 PM AST Fri Sep 14 2018 Isaac has rapidly lost organization since the last advisory. The cyclone has been devoid of any deep convection for most of the evening, with only a small burst recently forming well to the west of where Isaac's low-level center is believed to be located. While it is possible, if not likely, that the maximum winds have decreased a little since this afternoon due to the lack of convection, the initial intensity has been held at 35 kt based on earlier aircraft data. A NOAA Hurricane Hunter aircraft is scheduled to investigate Isaac again overnight and will provide a better estimate of the strength and status of Isaac. The global models continue to insist that Isaac could open into a trough at any time, and based on the current state of the cyclone, this could be imminent. The regional hurricane models, however, show the development of one or more mesoscale lows embedded within a larger cyclonic envelope that cause Isaac to persist for at least a few more days in those models. While the global model solution still seems more likely, I can't rule out that Isaac will persist a little longer, so the NHC forecast still carries a 72 h forecast point. Regardless of whether Isaac is a tropical storm or a tropical wave over the next few days, heavy rains and occasional gusty winds are still likely across much of the Greater Antilles through the next couple of days. It has been very difficult to try to pinpoint a low-level center of Isaac over the past few hours, but based on microwave data it appears to still be moving west at about 13 kt. The GFS and ECMWF are in very good agreement and show Isaac, or its remnants, moving steadily westward for the next several days. The regional models on the other hand show a farther north motion, in part due to one or more reformations of the center. The NHC forecast continues to favor the global model solutions and is on the south side of the guidance envelope, however if it becomes clear that Isaac will survive longer, a northward adjustment may be required in later advisories. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 15.4N 69.5W 35 KT 40 MPH 12H 15/1200Z 15.5N 71.3W 35 KT 40 MPH 24H 16/0000Z 15.7N 73.3W 35 KT 40 MPH 36H 16/1200Z 16.2N 75.3W 35 KT 40 MPH 48H 17/0000Z 16.7N 77.4W 30 KT 35 MPH 72H 18/0000Z 18.7N 81.4W 30 KT 35 MPH 96H 19/0000Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Helene Forecast Discussion Number 31

2018-09-15 04:36:30| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 14 2018 033 WTNT43 KNHC 150236 TCDAT3 Tropical Storm Helene Discussion Number 31 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Fri Sep 14 2018 Data from a timely ASCAT pass indicate that Helene still carries winds of 60 kt, primarily in the eastern semicircle. The cloud pattern continues to show a low-level center just south of the main convection, marking the strong shear which is affecting the system. Guidance indicates that Helene will not change much in intensity in the next 12 hours, and only a slight decrease in the winds is anticipated after that time. The wind field is forecast to expand mainly in the southeast quadrant, which is the area of the cyclone that most likely will affect the Azores. After passing to the north of, or near, the Azores in about 24 hours, Helene will be moving over cold waters and become post-tropical. The cyclone should be absorbed by a larger extratropical low, as the cyclone quickly approaches Ireland and the United Kingdom. Satellite fixes indicate that Helene is moving toward the north-northeast or 030 degrees at about 16 kt. Helene is embedded within the fast southwesterly flow ahead of a sharp mid-level trough and this pattern should steer the cyclone toward the northeast with a gradual increase in forward speed. Track guidance is very consistent with this solution, and the NHC forecast continues in the middle of the tight guidance envelope. Helene is expected to be a post-tropical cyclone when it approaches Ireland and the United Kingdom in a few days. Interests in those locations should consult products from their local meteorological service for information about potential impacts from Helene. Local forecasts and warnings for the UK can be found on the website of the UK Met Office at https://www.metoffice.gov.uk/. Local forecasts and warnings for Ireland can be found on the website of Met Eireann at https://www.met.ie/. FORECAST POSITIONS AND MAX WINDS INIT 15/0300Z 35.8N 35.8W 60 KT 70 MPH 12H 15/1200Z 38.0N 34.5W 60 KT 70 MPH 24H 16/0000Z 40.3N 31.2W 55 KT 65 MPH 36H 16/1200Z 42.5N 26.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 17/0000Z 45.0N 21.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 18/0000Z 51.5N 9.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 19/0000Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Florence Forecast Discussion Number 62

2018-09-15 00:19:15| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Sep 14 2018 ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM Tropical Storm Florence Discussion Number 62 NWS National Hurricane Center Miami FL AL062018 500 PM EDT Fri Sep 14 2018 Florence's satellite appearance continues to be quite impressive with well-established outflow and a nearly symmetrical cloud pattern. In radar imagery, however, the inner-core convection has continued to weaken and the echoes are now more stratiform in nature, while outer banding remains rather vigorous, especially south of Cape Lookout and Morehead City, North Carolina. An eye is no longer evident, and the pressure has continued to rise to a now estimated to be 972 mb based on nearby surface observations. Air Force Reserve aircraft data, NOAA Doppler weather radar velocity data from Wilmington, and nearby surface observations indicate that Florence's intensity has decreased to 60 kt, tropical storm status. Florence has turned westward and the motion estimate is now 270/03 kt. The new 1200Z global and regional model guidance is in good agreement on Florence moving slowly in a general westward direction for the next 48 hours or so, followed by a northward motion on day 3 as the system moves around the western periphery of a narrow subtropical ridge. On days 4 and 5, the cyclone is forecast to turn northeastward and accelerate ahead of an approaching shortwave trough and frontal system, and emerge off the northeast U.S. coast as an extratropical low. The new official forecast track is very similar to the previous advisory, and is lies near the northern and eastern edge of model guidance envelope, is closer to the TVCA/TVCN consensus models. Florence is expected to only slowly weaken overnight due to its proximity to the warm Atlantic where convective bands are expected to continue to develop and propagate inland in the eastern and southern portion of the circulation, which will act to bring down some of the stronger winds aloft. It is worth noting that the last reconnaissance pass indicated 700-mb flight-level winds of 77 kt just east of Charleston, South Carolina, so it won't take much convection to bring down some of those stronger winds to the surface as gusts. More rapid weakening is forecast over the weekend as Florence moves westward across the higher terrain of central and northwestern South Carolina. The official intensity forecast follows the weakening trend of the previous advisory, and is similar to an average of the GFS- and ECMWF-based Decay SHIPS models. Although coastal storm surge flooding will gradually subside tonight and Saturday, it cannot be emphasized enough that another serious hazard associated with slow-moving Florence will continue to be extremely heavy rainfall. More than 16 inches of rain has already fallen in many areas across southeastern North Carolina, and more rain is still to come, which will cause disastrous flooding that will spread inland through the weekend. Key Messages: 1. Life-threatening storm surge will continue along portions of the North Carolina coast through tonight, and also along the Neuse and Pamlico Rivers in western Pamlico Sound, where rainfall and freshwater flooding will also contribute to high water levels. Dangerous storm surge could also affect portions of the northeast coast of South Carolina coast tonight. 2. Life-threatening, catastrophic flash floods and prolonged significant river flooding are likely over portions of the Carolinas and the southern to central Appalachians from western North Carolina into southwest Virginia through early next week, as Florence moves slowly inland. In addition to the flash flood and flooding threat, mudslides are also possible in the higher terrain of the southern and central Appalachians across western North Carolina into southwest Virginia. 3. Tropical storm conditions will continue along the coast within the tropical storm warning area and also well inland across portions of South Carolina and North Carolina. 4. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 34.0N 78.6W 60 KT 70 MPH...INLAND 12H 15/0600Z 33.9N 79.3W 50 KT 60 MPH...INLAND 24H 15/1800Z 33.9N 80.3W 40 KT 45 MPH...INLAND 36H 16/0600Z 34.4N 81.4W 25 KT 30 MPH...INLAND 48H 16/1800Z 35.5N 82.6W 25 KT 30 MPH...INLAND 72H 17/1800Z 38.5N 82.6W 20 KT 25 MPH...POST-TROP/INLAND 96H 18/1800Z 41.5N 76.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 19/1800Z 44.0N 64.5W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart NNNN

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Tropical Storm Florence Forecast Discussion Number 62

2018-09-14 22:55:56| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Sep 14 2018 913 WTNT41 KNHC 142055 TCDAT1 Tropical Storm Florence Discussion Number 62 NWS National Hurricane Center Miami FL AL062018 500 PM EDT Fri Sep 14 2018 Florence's satellite appearance continues to be quite impressive with well-established outflow and a nearly symmetrical cloud pattern. In radar imagery, however, the inner-core convection has continued to weaken and the echoes are now more stratiform in nature, while outer banding remains rather vigorous, especially south of Cape Lookout and Morehead City, North Carolina. An eye is no longer evident, and the pressure has continued to rise to a now estimated to be 972 mb based on nearby surface observations. Air Force Reserve aircraft data, NOAA Doppler weather radar velocity data from Wilmington, and nearby surface observations indicate that Florence's intensity has decreased to 60 kt, tropical storm status. Florence has turned westward and the motion estimate is now 270/03 kt. The new 1200Z global and regional model guidance is in good agreement on Florence moving slowly in a general westward direction for the next 48 hours or so, followed by a northward motion on day 3 as the system moves around the western periphery of a narrow subtropical ridge. On days 4 and 5, the cyclone is forecast to turn northeastward and accelerate ahead of an approaching shortwave trough and frontal system, and emerge off the northeast U.S. coast as an extratropical low. The new official forecast track is very similar to the previous advisory, and is lies near the northern and eastern edge of model guidance envelope, is closer to the TVCA/TVCN consensus models. Florence is expected to only slowly weaken overnight due to its proximity to the warm Atlantic where convective bands are expected to continue to develop and propagate inland in the eastern and southern portion of the circulation, which will act to bring down some of the stronger winds aloft. It is worth noting that the last reconnaissance pass indicated 700-mb flight-level winds of 77 kt just east of Charleston, South Carolina, so it won't take much convection to bring down some of those stronger winds to the surface as gusts. More rapid weakening is forecast over the weekend as Florence moves westward across the higher terrain of central and northwestern South Carolina. The official intensity forecast follows the weakening trend of the previous advisory, and is similar to an average of the GFS- and ECMWF-based Decay SHIPS models. Although coastal storm surge flooding will gradually subside tonight and Saturday, it cannot be emphasized enough that another serious hazard associated with slow-moving Florence will continue to be extremely heavy rainfall. More than 16 inches of rain has already fallen in many areas across southeastern North Carolina, and more rain is still to come, which will cause disastrous flooding that will spread inland through the weekend. Key Messages: 1. Life-threatening storm surge will continue along portions of the North Carolina coast through tonight, and also along the Neuse and Pamlico Rivers in western Pamlico Sound, where rainfall and freshwater flooding will also contribute to high water levels. Dangerous storm surge could also affect portions of the northeast coast of South Carolina coast tonight. 2: Life-threatening, catastrophic flash floods and prolonged significant river flooding are likely over portions of the Carolinas and the southern to central Appalachians from western North Carolina into southwest Virginia through early next week, as Florence moves slowly inland. In addition to the flash flood and flooding threat, mudslides are also possible in the higher terrain of the southern and central Appalachians across western North Carolina into southwest Virginia. 3. Tropical storm conditions will continue along the coast within the tropical storm warning area and also well inland across portions of South Carolina and North Carolina. 4. Large swells affecting Bermuda, portions of the U.S. East Coast, and the northwestern and central Bahamas will continue this week, resulting in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 34.0N 78.6W 60 KT 70 MPH...INLAND 12H 15/0600Z 33.9N 79.3W 50 KT 60 MPH...INLAND 24H 15/1800Z 33.9N 80.3W 40 KT 45 MPH...INLAND 36H 16/0600Z 34.4N 81.4W 25 KT 30 MPH...INLAND 48H 16/1800Z 35.5N 82.6W 25 KT 30 MPH...INLAND 72H 17/1800Z 38.5N 82.6W 20 KT 25 MPH...POST-TROP/INLAND 96H 18/1800Z 41.5N 76.0W 20 KT 25 MPH...POST-TROP/INLAND 120H 19/1800Z 44.0N 64.5W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

Tags: number discussion storm tropical

 

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