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Hurricane Teddy Forecast Discussion Number 24

2020-09-18 10:36:03| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Sep 18 2020 000 WTNT45 KNHC 180835 TCDAT5 Hurricane Teddy Discussion Number 24 NWS National Hurricane Center Miami FL AL202020 500 AM AST Fri Sep 18 2020 Teddy remains a powerful category 4 hurricane with a well-defined eye and intense eyewall. There have been occasional dry slots that have eroded some of the convection in the eyewall and rain bands, but these seem to be transient. The satellite intensity estimates currently range from 90 kt to 128 kt, and based on a blend of that data, the initial intensity is set at 115 kt for this advisory. The hurricane is moving northwestward at 11 kt. Teddy is expected to continue moving northwestward at about the same forward speed during the next couple of days as it moves on the southwestern periphery of a subtropical high pressure system. By the end of the weekend, when Teddy will likely be approaching Bermuda, a turn to the north or north-northeast is forecast to occur as a mid- to upper-level trough moves closer to the system. However, the trough is expected to cut off, causing Teddy to turn slightly to the left early next week and approach Atlantic Canada in 4 to 5 days. The models are in fairly good agreement, and only small changes were made to the previous NHC track prediction. The major hurricane will likely maintain its intensity, or fluctuate in strength, during the next day or so while it remains in generally favorable conditions of low wind shear, warm waters, and a fairly moist air mass. However, the intensity models all show a slow weakening trend after that likely due to Teddy tracking over the cool SST wake left behind from Paulette and an increase in shear by early next week. Teddy is now forecast to transition to a powerful extratropical cyclone by the end of the forecast period based on the global model guidance. The NHC intensity forecast lies near the high end of the guidance envelope, in best agreement with the LGEM dynamical-statistical model. Teddy is producing a large area of high seas. The maximum seas estimated by TAFB near the core of the hurricane are around 40 feet. Swells from Teddy are spreading far from the center, see Key Messages below. Key Messages: 1. Teddy is expected to approach Bermuda as a hurricane this weekend and make its closest approach to the island late Sunday or Monday. While the exact details of Teddy's track and intensity near the island are not yet known, the risk of strong winds, storm surge, and heavy rainfall on Bermuda is increasing. 2. Large swells produced by Teddy are expected to affect portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, and the southeastern United States during the next few days. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 21.6N 55.4W 115 KT 130 MPH 12H 18/1800Z 22.8N 56.5W 120 KT 140 MPH 24H 19/0600Z 24.7N 58.1W 115 KT 130 MPH 36H 19/1800Z 26.6N 59.9W 110 KT 125 MPH 48H 20/0600Z 28.2N 61.6W 105 KT 120 MPH 60H 20/1800Z 29.8N 62.7W 100 KT 115 MPH 72H 21/0600Z 32.2N 62.8W 95 KT 110 MPH 96H 22/0600Z 39.7N 61.9W 90 KT 105 MPH 120H 23/0600Z 46.0N 62.9W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi

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Tropical Depression Twenty-two Forecast Discussion Number 2

2020-09-18 04:43:29| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Thu Sep 17 2020 000 WTNT42 KNHC 180243 TCDAT2 Tropical Depression Twenty-Two Discussion Number 2 NWS National Hurricane Center Miami FL AL222020 1000 PM CDT Thu Sep 17 2020 Inspection of flight-level wind data from the earlier Air Force Reserve mission indicates that the depression has a somewhat elongated circulation, but a sufficiently well-defined center and pressure minimum were found just to the west of NOAA buoy 42055. The plane measured maximum surface winds of 30 kt in the deep convection to the southwest of the center using the SFMR instrument, and that remains the initial intensity. As best as I can tell, the depression is moving very slowly northeastward with an initial motion of 035/3 kt. A positively tilted mid- to upper-level trough extends across Texas and northern Mexico, and this feature should cause the depression to move toward the north-northeast during the next 36 hours. The trough is expected to dissolve soon after that time, with a mid-tropospheric high building over the south-central United States. The high should force the cyclone to turn and move very slowly westward on days 3 and 4, and then potentially stall or meander off the lower Texas/ northeastern Mexico coast by day 5. There is lower-than-normal confidence in the official track forecast due to fairly significant spread among the track guidance. However, the models do agree on the general scenario, and they all suggest that the depression is unlikely to move a whole lot for the entire forecast period. This new NHC forecast lies very close to the TVCN multi-model consensus. Unfortunately, there is also significant uncertainty in the intensity forecast. Light-to-moderate southerly to southwesterly shear is expected to affect the depression for the next couple of days while it moves over very warm waters of 30-31 degrees Celsius and in a very moist environment. Things change quickly after 48 hours due to a cold front entering the northern Gulf, and the drier, more stable air mass behind the front could be entrained into the cyclone's circulation from day 3 to day 5. The GFS- and ECMWF-based SHIPS models show the most significant strengthening, bringing the intensity to 75-80 kt in about 3 days, while many of the other intensity models don't even raise it to hurricane intensity. As a compromise between these various solutions, the NHC intensity forecast shows the cyclone just reaching the hurricane threshold in 2-3 days and then gradually weakening thereafter due to the less favorable environment. However, it cannot be stressed enough that this forecast is highly uncertain. Key Messages: 1. Tropical Depression Twenty-Two is expected to strengthen to a tropical storm, and possibly a hurricane, while moving slowly over the western Gulf of Mexico during the next few days. 2. While it is too early to determine what areas could see direct wind, storm surge, and rainfall impacts from this system, interests throughout the western Gulf of Mexico should monitor the progress of this system and future updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 22.0N 94.2W 30 KT 35 MPH 12H 18/1200Z 22.9N 93.8W 35 KT 40 MPH 24H 19/0000Z 23.9N 93.3W 45 KT 50 MPH 36H 19/1200Z 24.8N 92.9W 55 KT 65 MPH 48H 20/0000Z 25.4N 93.2W 60 KT 70 MPH 60H 20/1200Z 25.6N 94.0W 65 KT 75 MPH 72H 21/0000Z 25.7N 94.8W 65 KT 75 MPH 96H 22/0000Z 26.1N 95.9W 60 KT 70 MPH 120H 23/0000Z 26.4N 96.0W 55 KT 65 MPH $$ Forecaster Berg

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Tropical Depression Twenty-two Forecast Discussion Number 1

2020-09-18 01:00:25| National Hurricane Center (Atlantic)

Issued at 600 PM CDT Thu Sep 17 2020 000 WTNT42 KNHC 172300 TCDAT2 Tropical Depression Twenty-Two Special Discussion Number 1 NWS National Hurricane Center Miami FL AL222020 600 PM CDT Thu Sep 17 2020 Reports from an Air Force Reserve Hurricane Hunter aircraft indicate that the low pressure area over the southwestern Gulf of Mexico has developed a sufficiently well-defined circulation, with SFMR wind data suggesting an intensity of about 30 kt. In addition, the associated convection is organized enough for SAB and TAFB to provide Dvorak satellite intensity estimates of 30 kt. Based on this information, advisories are being initiated on Tropical Depression Twenty-Two. The initial motion is a somewhat uncertain 035/4. During the next 48 h or so, the cyclone should be steered slowly north-northeastward by a mid- to upper-level trough over Texas and northern Mexico. After that time, the global models are in good agreement that this trough will weaken and lift out to the northeast, with a weak mid-level ridge building to the north of the cyclone. This should result in a gradual turn toward the west at a continued slow forward speed. Although the cyclone is relatively close to land, the vast majority of the track guidance keeps the system offshore for the next five days. The official forecast will follow this scenario, with the forecast track being between the HCCA corrected consensus and the other consensus models. The large-scale models suggest that the cyclone will be in an environment of light to moderate vertical wind shear for the next several days. Some dry air entrainment may occur after 48 h. The bulk of the intensity guidance keeps the system below hurricane strength during the forecast period. The official intensity forecast follows the trend of the guidance and shows the system peaking as a tropical storm, but it lies a little above the intensity consensus. As mentioned above, the cyclone is likely to stay offshore during the forecast period. Therefore, it is too early to tell which parts of the coast of the Gulf of Mexico will get wind, storm surge, and rain impacts from this system Key Messages: 1. The system is expected to strengthen to a tropical storm while moving slowly over the western Gulf of Mexico during the next few days. 2. While it is too early to determine what areas could see direct wind, storm surge, and rainfall impacts from this system, interests throughout the western Gulf of Mexico should monitor the progress of this system and future updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 17/2300Z 21.9N 94.3W 30 KT 35 MPH 12H 18/0600Z 22.7N 94.0W 30 KT 35 MPH 24H 18/1800Z 23.8N 93.5W 35 KT 40 MPH 36H 19/0600Z 24.8N 93.0W 45 KT 50 MPH 48H 19/1800Z 25.4N 92.9W 55 KT 65 MPH 60H 20/0600Z 25.8N 93.1W 60 KT 70 MPH 72H 20/1800Z 26.1N 93.8W 60 KT 70 MPH 96H 21/1800Z 26.1N 95.1W 55 KT 65 MPH 120H 22/1800Z 25.6N 96.1W 50 KT 60 MPH $$ Forecaster Berg/Beven

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Hurricane Teddy Forecast Discussion Number 22

2020-09-17 22:58:21| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Sep 17 2020 588 WTNT45 KNHC 172058 TCDAT5 Hurricane Teddy Discussion Number 22 NWS National Hurricane Center Miami FL AL202020 500 PM AST Thu Sep 17 2020 Teddy has intensified quickly today, with the cyclone now having a more symmetrical appearance while the eye has become mostly clear. The deep convection with cloud tops ranging from -60 to -75 degrees have surrounded the eye for much of the day, and there are well-defined outflow channels to the south and east of the hurricane. Both NOAA and US Air Force Reserve Hurricane Hunter aircraft have spent time investigating Teddy today as it has been intensifying and have been able to provide very useful data in determining both the size and strength of the hurricane. The peak SFMR winds measured by the aircraft this afternoon were 113 kt, while the peak 700 mb flight-level winds were 130 kt. Based on a reduction to 117 kt from 700 mb, and assuming some slight undersampling may be occurring, the initial intensity has been raised to 120 kt. The hurricane is expected to remain in an environment of low-moderate shear while over warm waters for the 48 h or so. And since the period of rapid strengthening of Teddy appears to be ongoing, the hurricane is expected to strengthen some more into tonight. Once this round of intensification completes, there will likely be some fluctuations in strength due to eyewall replacement cycles and other short term changes in structure. After 48 h, the path of Teddy should take it over some cooler waters caused by upwelling from Hurricane Paulette last week. This should cause the cyclone to slowly weaken. By 96 h, vertical wind shear is forecast to increase ahead of an approaching mid-latitude trough and associated frontal boundary. This should hasten the weakening trend of Teddy. By 120 h, the hurricane is expected to have crossed the 26 degree SST isotherm, and will begin to interact with the aforementioned mid-latitude system causing it to begin an extratropical transition that may or may not be completed by the end of the forecast period. The latest NHC intensity forecast has been increased due to the higher initial intensity, and the forecast trends fit well with the various intensity consensus and SHIPS guidance. Teddy continues its northwestward motion, now at 11 kt. The track guidance is in very good agreement on a continuation of this motion for the next 72 h as the cyclone is steered by a mid-level ridge over the central Atlantic. The model guidance has come into better agreement on the evolution of the large scale features later on in the forecast period as the hurricane is expected to recurve ahead of the approaching mid-latitude trough moving off the coast of the eastern United States in a few days. The new NHC track forecast is little changed from the previous one, and is in the middle of the track guidance. On the forecast track, Teddy will make its closest approach to Bermuda Sunday night into Monday. Key Messages: 1. Teddy is expected to approach Bermuda as a hurricane this weekend and make its closest approach to the island late Sunday or Monday. While the exact details of Teddy's track and intensity near the island are not yet known, the risk of strong winds, storm surge, and heavy rainfall on Bermuda is increasing. 2. Large swells produced by Teddy are expected to affect portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, and the southeastern United States late this week and into the weekend. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 20.1N 54.1W 120 KT 140 MPH 12H 18/0600Z 21.2N 55.2W 130 KT 150 MPH 24H 18/1800Z 22.8N 56.6W 125 KT 145 MPH 36H 19/0600Z 24.5N 58.1W 125 KT 145 MPH 48H 19/1800Z 26.3N 59.9W 120 KT 140 MPH 60H 20/0600Z 28.0N 62.1W 110 KT 125 MPH 72H 20/1800Z 29.5N 63.3W 105 KT 120 MPH 96H 21/1800Z 33.9N 63.0W 95 KT 110 MPH 120H 22/1800Z 41.3N 62.0W 80 KT 90 MPH $$ Forecaster Latto

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Post-Tropical Cyclone Vicky Forecast Discussion Number 15

2020-09-17 22:39:57| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Sep 17 2020 000 WTNT41 KNHC 172039 TCDAT1 Post-Tropical Cyclone Vicky Discussion Number 15 NWS National Hurricane Center Miami FL AL212020 500 PM AST Thu Sep 17 2020 There has not been any organized deep convection near the center of Vicky in more than 12 hours as very strong vertical wind shear continues to take a toll on the cyclone. Vicky has become a swirl of low clouds and no longer meets the definition of a tropical cyclone. Therefore, the system is being declared a remnant low and this will be the last NHC advisory on Vicky. The Dvorak CI-number from TAFB suggests that the intensity of the system has fallen to 25 kt, which is the basis for the advisory wind speed. Very strong vertical wind shear associated with outflow from Hurricane Teddy is expected to continue to cause the remnant low to weaken, and the system is expected to degenerate into a trough of low pressure in 24 to 36 hours. The official forecast follows suit and calls for dissipation by early Saturday. Vicky is now moving west-southwestward or 250/10 kt. The remnant low should remain on a west-southwestward heading while it is steered by the low-level northeasterly trade wind flow over the next day or so. The latest NHC track forecast is near the various consensus aids and in the middle of the tightly clustered dynamical models. This is the last NHC advisory on Vicky. Additional information on the remnant low can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 21.1N 39.1W 25 KT 30 MPH...POST-TROPICAL 12H 18/0600Z 20.6N 40.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 18/1800Z 19.9N 42.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 19/0600Z...DISSIPATED $$ Forecaster Brown

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