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Tropical Depression Joyce Forecast Discussion Number 17

2018-09-16 22:33:16| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 16 2018 344 WTNT45 KNHC 162033 TCDAT5 Tropical Depression Joyce Discussion Number 17 NWS National Hurricane Center Miami FL AL102018 500 PM AST Sun Sep 16 2018 Joyce continues to hang on as a tropical depression. The cloud pattern consists of a swirl of low-level clouds with patches of deep convection that become sheared off in the northeast quadrant. The initial intensity is held at 30 kt, in agreement with an ASCAT pass from several hours ago that showed maximum winds in the 25-30 kt range. Even though Joyce is over relatively warm water, the current hostile atmospheric environment of 30-40 kt of west-southwesterly shear and nearby dry air should cause Joyce to gradually weaken during the next few days. Although remnant low status is not predicted to occur for 2-3 days, it is very possible that Joyce could degenerate into a trough or a remnant low well before then. The depression has turned to the east, with the latest initial motion estimate being 090/15. The weak and shallow system is expected to move in the low- to mid-level flow during the next few days. This should cause the cyclone to slow down and turn southeastward on Monday, followed by a southward and then southwestward motion on Tuesday and Wednesday as the system moves around a building ridge over the northeastern Atlantic. The track models are in fairly good agreement, and only small changes were made to the previous NHC forecast. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 34.4N 32.6W 30 KT 35 MPH 12H 17/0600Z 34.2N 30.2W 30 KT 35 MPH 24H 17/1800Z 33.6N 28.0W 30 KT 35 MPH 36H 18/0600Z 32.4N 27.0W 25 KT 30 MPH 48H 18/1800Z 31.2N 27.4W 25 KT 30 MPH 72H 19/1800Z 29.4N 30.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 20/1800Z...DISSIPATED $$ Forecaster Cangialosi

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Post-Tropical Cyclone Helene Forecast Discussion Number 37

2018-09-16 16:43:14| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Sep 16 2018 413 WTNT43 KNHC 161443 TCDAT3 Post-Tropical Cyclone Helene Discussion Number 37 NWS National Hurricane Center Miami FL AL082018 1100 AM AST Sun Sep 16 2018 Helene's cloud pattern has transformed into that of an extratropical cyclone, with a large area of cold cloud tops located well to the north and northwest of the center. An ASCAT pass that caught the eastern portion of the circulation revealed maximum winds of 40 to 45 kt, therefore the initial wind speed remains 45 kt for this advisory. The global models suggest that the system will strengthen slightly today due to baroclinic processes, and this is reflected in the official forecast. Weakening is anticipated by late Monday, and the system is forecast to be absorbed by a larger low pressure to the northwest of the United Kingdom by Tuesday morning. The cyclone is moving quickly northeastward or 055/25 kt. Now that the system is embedded within the mid-latitude westerlies, a northeastward motion with some additional increase in forward speed is expected over the next day or so. The global models remain in good agreement on the track of the post-tropical low, and the new official forecast is an update of the previous advisory. This is the last NHC advisory on this system. Interests in Ireland and the United Kingdom should consult products from their local meteorological service for information about potential impacts from the post-tropical cyclone. 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 16/1500Z 43.8N 25.7W 45 KT 50 MPH...POST-TROPICAL 12H 17/0000Z 45.8N 21.2W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 17/1200Z 49.0N 14.8W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 18/0000Z 52.8N 6.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 48H 18/1200Z...ABSORBED $$ Forecaster Brown

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Tropical Depression Joyce Forecast Discussion Number 16

2018-09-16 16:41:48| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Sep 16 2018 947 WTNT45 KNHC 161441 TCDAT5 Tropical Depression Joyce Discussion Number 16 NWS National Hurricane Center Miami FL AL102018 1100 AM AST Sun Sep 16 2018 Joyce is barely a tropical cyclone at the moment. The cloud pattern consists of a low-level swirl with a small patch of deep convection located about 80 n mi northeast of the center and another patch of weakening convection well removed from the center in the northeast quadrant. Visible satellite images and a partial ASCAT pass indicate that the circulation of the cyclone has also become increasingly elongated from northeast to southwest. Based on the system's appearance and the satellite intensity estimates, the initial wind speed is lowered to 30 kt, making Joyce a tropical depression. The depression is moving east-northeastward at 16 kt within the mid-latitude westerlies, and this motion should continue through tonight. After that time, the shallow cyclone is expected to slow down and turn southeastward and then southwestward as it is moves in the flow on the east side of a building low- to mid-level ridge. The track models are in fairly good agreement, and little overall change was made to the previous NHC forecast. Joyce is currently in a quite hostile environment of 30-40 kt of west-southwesterly shear. Even though SSTs are relatively warm, the ongoing strong shear and nearby dry air should continue to cause the cyclone to gradually weaken. Although the NHC forecast shows Joyce hanging on as a tropical depression for a couple of more days, it is very possible that the system could degenerate into a trough or a remnant low at any time during that period. FORECAST POSITIONS AND MAX WINDS INIT 16/1500Z 34.7N 34.3W 30 KT 35 MPH 12H 17/0000Z 34.9N 31.4W 30 KT 35 MPH 24H 17/1200Z 34.5N 28.7W 30 KT 35 MPH 36H 18/0000Z 33.6N 27.0W 30 KT 35 MPH 48H 18/1200Z 32.6N 26.7W 25 KT 30 MPH 72H 19/1200Z 30.4N 29.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 20/1200Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Florence Forecast Discussion Number 68

2018-09-16 10:48:09| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun Sep 16 2018 635 WTNT41 KNHC 160848 TCDAT1 Tropical Depression Florence Discussion Number 68 NWS National Hurricane Center Miami FL AL062018 500 AM EDT Sun Sep 16 2018 Surface observations indicate that there are no longer any sustained tropical-storm-force winds as the center of Florence has moved farther inland over South Carolina. Therefore, the system is being downgraded to a tropical depression at this time. Maximum winds are estimated to be 30 kt. Continued gradual weakening is likely, and the numerical guidance suggests that the cyclone will be disorganized enough to become a remnant low in 36 hours or so. In 72 hours, global models indicate that the system will become an extratropical cyclone, with some strengthening due to baroclinic processes as it moves over the Atlantic in 3-5 days. This scenario is very similar to that from the previous advisory. The forward speed of Florence has increased somewhat early this morning and the motion is now near 280/7 kt. The high pressure system that has been blocking the forward progress of Florence is predicted to slide eastward and southeastward during the next day or so. As a result, over the next couple of days, Florence is expected to move northwestward, northward, and then north-northeastward around the periphery of the high. Later in the forecast period, Florence should accelerate east-northeastward in the mid-latitude westerlies. The official track forecast is similar to the previous one and close to the dynamical model consensus. This will be the last advisory issued by the National Hurricane Center on Florence. Future information on Florence can be found in Public Advisories issued by the Weather Prediction Center beginning at 11 AM EDT, under AWIPS header TCPAT1, WMO header WTNT31 KWNH, and on the web at https://www.wpc.ncep.noaa.gov. Key Messages: 1. 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 this week, as Florence continues to move 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. 2. 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 16/0900Z 33.8N 81.4W 30 KT 35 MPH...INLAND 12H 16/1800Z 34.7N 82.5W 30 KT 35 MPH...INLAND 24H 17/0600Z 36.7N 83.6W 25 KT 30 MPH...INLAND 36H 17/1800Z 38.7N 82.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 18/0600Z 39.8N 79.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 19/0600Z 42.0N 68.0W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 20/0600Z 43.5N 55.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 21/0600Z 46.0N 40.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Tropical Storm Joyce Forecast Discussion Number 15

2018-09-16 10:44:41| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Sep 16 2018 075 WTNT45 KNHC 160844 TCDAT5 Tropical Storm Joyce Discussion Number 15 NWS National Hurricane Center Miami FL AL102018 500 AM AST Sun Sep 16 2018 What's left of the Joyce's associated deep convection is now displaced about 80 miles to the north-northeast of the elongated surface circulation. There still may be some 35 kt winds in a small area of deep convection where the coldest cloud tops (-65C) are observed, therefore, the initial intensity is held at 35 kt for this advisory. There is no change to the intensity forecast philosophy. The surrounding environment is forecast to remains quite unfavorable during the next 24 hours, although the warm 27C oceanic temperatures could slightly counteract the negative effects of the harsh vertical shear pattern. Afterward, decreasing sea surface temperatures, a more stable thermodynamic air mass, along with the stiff shear, is forecast to induce gradual weakening and, ultimately, dissipation in 4 days. The initial motion is estimated to be east-northeastward, or 075/15 kt. The cyclone is embedded within the same mid-tropospheric steering flow as Tropical Storm Helene, and Joyce should move east-northeastward to eastward today. Through day 3, Joyce should turn southeastward to south-southwestward around the eastern periphery of a subtropical ridge to its west as a vertically shallow system. The NHC forecast is similar to the previous advisory, and is based on the better-performing consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 34.0N 36.1W 35 KT 40 MPH 12H 16/1800Z 34.5N 33.4W 30 KT 35 MPH 24H 17/0600Z 34.6N 30.1W 30 KT 35 MPH 36H 17/1800Z 34.1N 27.8W 30 KT 35 MPH 48H 18/0600Z 32.9N 26.8W 25 KT 30 MPH 72H 19/0600Z 30.7N 28.5W 25 KT 30 MPH 96H 20/0600Z...DISSIPATED $$ Forecaster Roberts

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