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Tropical Storm Florence Forecast Discussion Number 64

2018-09-15 10:51:34| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sat Sep 15 2018 485 WTNT41 KNHC 150851 TCDAT1 Tropical Storm Florence Discussion Number 64 NWS National Hurricane Center Miami FL AL062018 500 AM EDT Sat Sep 15 2018 Florence is slowly weakening while its center remains inland over extreme eastern South Carolina. However, WSR-88D Doppler radar still shows some intense bands of convection over the eastern portion of the circulation, and these bands have been training over the coast of North Carolina overnight. Based on current Doppler velocities of 55-60 kt at around 5500 ft, the current intensity is set at 45 kt. The system should continue to weaken as it moves farther inland today, and it is anticipated that Florence will become a tropical depression tonight. The official intensity forecast is similar to the Decay-SHIPS model guidance through around day 3. By days 4 and 5, the post-tropical cyclone is forecast to strengthen somewhat due to baroclinic processes after moving off the New England coast and passing near southern Atlantic Canada. Radar and satellite fixes indicate that Florence continues its west-southwestward motion at around 255/4 kt. A mid-level high pressure area to the northwest of Florence is forecast to shift to the north, northeast, and east of the cyclone over the next couple of days. As a result, Florence should turn northwestward and northward, and then north-northeastward through 72 hours. Late in the forecast period, the system is expected to accelerate east-northeastward in the mid-latitude westerlies. The official forecast is somewhat faster than the previous one at days 4 and 5 but is in good agreement with the latest global model runs. Although coastal storm surge flooding will gradually subside today, extremely heavy rainfall will continue to be a serious hazard associated with slow-moving Florence. More than a foot of rain has already fallen across portions of 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 today, 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 today. 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 west-central Virginia and far eastern West Virginia through early next week, as Florence moves slowly inland. In addition to the flash flood and flooding threat, landslides 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 today. 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 15/0900Z 33.6N 79.5W 45 KT 50 MPH 12H 15/1800Z 33.6N 80.2W 40 KT 45 MPH...INLAND 24H 16/0600Z 33.9N 81.3W 30 KT 35 MPH...INLAND 36H 16/1800Z 35.1N 82.4W 25 KT 30 MPH...INLAND 48H 17/0600Z 37.0N 83.5W 25 KT 30 MPH...INLAND 72H 18/0600Z 40.5N 80.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/0600Z 43.5N 68.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 20/0600Z 47.0N 54.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Tropical Storm Joyce Forecast Discussion Number 11

2018-09-15 10:44:04| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Sep 15 2018 082 WTNT45 KNHC 150843 TCDAT5 Tropical Storm Joyce Discussion Number 11 NWS National Hurricane Center Miami FL AL102018 500 AM AST Sat Sep 15 2018 There has not much change with Joyce overnight. The tropical storm is producing a fair amount of deep convection to the north and west of the center, but there are some dry slots on the east side. A blend of the latest satellite intensity estimates supports holding the initial wind speed at 45 kt. Joyce is currently just east of an upper-level trough and the flow aloft is quite diffluent near the cyclone. This upper-level pattern could allow Joyce to strengthen slightly today. However, by tonight, southwesterly flow aloft is expected to increase over the cyclone. This increase in shear combined with decreasing mid-level humidities and cooling SSTs should lead to a steady weakening trend after 12 hours. The cyclone is forecast to dissipate in 3 to 4 days, but some of the models suggest that this could occur sooner. The tropical storm is moving eastward at 7 kt. Joyce is embedded in the same trough as Helene and it should follow that tropical cyclone east-northeastward to northeastward at increasing forward speeds during the next day or two. Beyond that time, if there is anything left of Joyce, the system will likely turn back to the east or east-southeast as it moves within the mid-latitude westerlies. The models are in fairly good agreement, and this forecast lies close to the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 31.9N 42.2W 45 KT 50 MPH 12H 15/1800Z 32.7N 40.6W 50 KT 60 MPH 24H 16/0600Z 33.9N 37.8W 45 KT 50 MPH 36H 16/1800Z 34.6N 34.1W 40 KT 45 MPH 48H 17/0600Z 34.7N 31.0W 35 KT 40 MPH 72H 18/0600Z 33.0N 26.5W 30 KT 35 MPH 96H 19/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Storm Helene Forecast Discussion Number 32

2018-09-15 10:42:02| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Sep 15 2018 247 WTNT43 KNHC 150841 TCDAT3 Tropical Storm Helene Discussion Number 32 NWS National Hurricane Center Miami FL AL082018 500 AM AST Sat Sep 15 2018 Helene appears to be maintaining its strength. Recent microwave images show that the storm has an eye feature, but the vortex is significantly tilted in the vertical due to southwesterly shear. Deep convection is most organized in bands to the north and west of the center. Based on the tropical storm's appearance in microwave images, the initial intensity is again held at 60 kt, near the high end of the satellite intensity estimates. Helene is expected to gradually weaken during the next few days due to the influences of southwesterly shear, drier air, and much cooler SSTs along the forecast track. These conditions should also cause Helene to lose tropical characteristics, and the storm is forecast become extratropical in 24 to 36 hours. The tropical storm is moving north-northeastward at a fairly fast pace, 19 kt. The center of Helene is expected to pass to the west of the Azores by tonight. However, Helene has a fairly large wind field, and tropical-storm-force winds are expected across the western Azores as the storm passes by. A shortwave trough to the northwest of the system is expected to approach Helene by tonight, and that should cause the cyclone to turn northeastward and then speed up in that direction as it heads toward Ireland and the United Kingdom late this weekend and early next week. The models are in fair agreement, and only small changes were made to the previous NHC track forecast. Helene is expected to be a post-tropical cyclone when it approaches Ireland and the United Kingdom in two to three 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 15/0900Z 37.7N 34.8W 60 KT 70 MPH 12H 15/1800Z 39.7N 32.7W 60 KT 70 MPH 24H 16/0600Z 41.8N 29.2W 55 KT 65 MPH 36H 16/1800Z 44.1N 24.3W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 17/0600Z 46.7N 18.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 72H 18/0600Z 55.8N 5.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 19/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Remnants of Isaac Forecast Discussion Number 31

2018-09-15 10:41:32| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sat Sep 15 2018 559 WTNT44 KNHC 150841 TCDAT4 Remnants Of Isaac Discussion Number 31 NWS National Hurricane Center Miami FL AL092018 500 AM EDT Sat Sep 15 2018 A NOAA Hurricane Hunter aircraft investigated Isaac over the past few hours and was unable to identify a well-defined center. The plane found multiple small and poorly-defined circulations embedded within a larger area of weak and variable winds, well to the south of the previous estimated center location. The plane also found that the minimum pressure has risen to around 1006 mb. All of this data confirmed what two late-arriving ASCAT overpasses from earlier this evening indicated, that Isaac has opened up into a southwest to northeast oriented trough. Since Isaac does not have a well-defined center, it no longer meets the NHC definition of a tropical cyclone and this is the last advisory. The strongest SFMR winds found by the plane were around 30 kt, mainly to the north of the deep convection, so the intensity has been set at that value. Although some of the regional hurricane models suggest that small short-lived circulations like the ones found by the plane could temporarily spin up within the larger envelope of the tropical wave over the next several days, none of the dynamical models currently show any significant redevelopment of Isaac. The wave will likely continue westward across the Caribbean Sea over the next few days, producing gusty winds and occasional heavy rains over portions of Hispaniola and Jamaica. This is the last public advisory issued by the National Hurricane Center on Isaac. Additional information can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and available online at https://ocean.weather.gov/shtml/NFDHSFAT1.shtml. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 14.8N 70.8W 30 KT 35 MPH 12H 15/1800Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Florence Forecast Discussion Number 63

2018-09-15 04:43:02| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Fri Sep 14 2018 573 WTNT41 KNHC 150242 TCDAT1 Tropical Storm Florence Discussion Number 63 NWS National Hurricane Center Miami FL AL062018 1100 PM EDT Fri Sep 14 2018 Although we lost data from the Wilmington, North Carolina, WSR-88D radar several hours ago, the radars from Raleigh and Columbia have clearly shown Florence's center has moved into extreme eastern South Carolina. Reflectivities around the eye have been decreasing, but there are still some strong spiral bands moving from southeast to northwest across portions of southeastern North Carolina. Maximum Doppler velocities are 65-70 kt from 5000-7000 feet, and on this basis Florence's maximum surface winds are estimated to be 55 kt. Radar fixes indicate that Florence has turned west-southwestward and has an initial motion of 255/4 kt. A mid-level high centered near Iowa and Missouri is expected to slide eastward to the north of Florence over the next 48 hours, which should cause the storm to maintain a slow motion and gradually turn toward the west and northwest over the Carolinas. For this period, the new official forecast track has been shifted a bit southward to follow an overall trend in the model guidance, but this isn't surprising given what some of the models were showing last night. After 48 hours, Florence is expected to get picked up by the mid-latitude westerlies, accelerating north and northeastward to the western Atlantic by day 5. The NHC track forecast is fairly close to the TVCN multi-model consensus and just a little south of the previous forecast beyond 72 hours. Florence's winds should continue to slowly decay as the center ambles farther inland, but enough of the circulation should remain over water to allow the cyclone to remain as a tropical storm for the next 24 hours or so. This thinking follows the global model fields of the GFS and ECMWF models. After 24 hours, most of Florence's circulation should be inland, allowing the cyclone to weaken to a tropical depression and eventually degenerate into a remnant low over the Ohio Valley by day 3. The remnant low is then likely to become an extratropical low by day 4, and it forecast to begin producing gale-force winds well east of New England to the south of Atlantic Canada. 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 a foot of rain has already fallen across portions of 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, landslides 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 through Saturday. 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 15/0300Z 33.8N 79.1W 55 KT 65 MPH...INLAND 12H 15/1200Z 33.7N 79.6W 45 KT 50 MPH...INLAND 24H 16/0000Z 33.8N 80.5W 35 KT 40 MPH...INLAND 36H 16/1200Z 34.4N 81.8W 30 KT 35 MPH...INLAND 48H 17/0000Z 35.9N 83.1W 25 KT 30 MPH...INLAND 72H 18/0000Z 39.3N 81.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/0000Z 41.0N 74.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 20/0000Z 43.5N 61.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg

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