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Hurricane Teddy Forecast Discussion Number 19

2020-09-17 04:43:07| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 16 2020 000 WTNT45 KNHC 170243 TCDAT5 Hurricane Teddy Discussion Number 19 NWS National Hurricane Center Miami FL AL202020 1100 PM AST Wed Sep 16 2020 Teddy has been a perplexing hurricane thus far. The infrared satellite presentation appears rather impressive, with the center embedded beneath a Central Dense Overcast with cloud tops as cold as -85 degrees Celsius. Despite the presentation, however, Dvorak estimates from TAFB and SAB are a consensus T4.5/77 kt, and objective estimates range between 70-75 kt. Teddy's initial intensity is therefore set just above these estimates at 80 kt. A recent ASCAT pass indicated that Teddy's center is a little farther to the southwest than previously estimated. However, the long-term motion remains toward the northwest (315/11 kt). The track forecast remains straightforward the the next 3 days, with the guidance in good agreement that a mid-tropospheric high over the central Atlantic will drive the hurricane northwestward toward the western Atlantic. There is a little more spread among the track models on days 4 and 5, related to timing differences on exactly where and how fast Teddy begins to recurve ahead of an approaching mid-latitude trough coming from the northeastern United States. The new NHC track forecast has been nudged westward during the first 3 days to account for the initial position adjustment, but otherwise it's still close to the previous prediction even with the increasing model spread on days 4 and 5. An upper-level trough situated to the northwest of Teddy is causing about 10-15 kt of deep-layer southwesterly shear over the hurricane, and some model analyses suggest that there could be stronger shear in a layer below the level of the upper-level outflow. The deep-layer shear is expected to increase a bit during the next day or so, but this should be offset by a favorable thermodynamic environment, allowing for some intensification during that time. The shear might relax by days 3 and 4, but then the thermodynamic environment becomes a little less conducive for strengthening. In particular, Teddy may move over the cold wake of Hurricane Paulette, and the SHIPS guidance indicates that relatively warm upper-level temperatures could be a negative factor. All that said, the NHC intensity forecast lies near the top end of the guidance envelope, showing Teddy peaking in intensity in a couple of days and then only gradually weakening through the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 17.8N 51.5W 80 KT 90 MPH 12H 17/1200Z 18.9N 52.6W 85 KT 100 MPH 24H 18/0000Z 20.3N 54.1W 95 KT 110 MPH 36H 18/1200Z 21.8N 55.6W 100 KT 115 MPH 48H 19/0000Z 23.5N 57.1W 100 KT 115 MPH 60H 19/1200Z 25.3N 59.1W 95 KT 110 MPH 72H 20/0000Z 27.0N 61.1W 95 KT 110 MPH 96H 21/0000Z 30.0N 64.0W 90 KT 105 MPH 120H 22/0000Z 35.0N 64.0W 90 KT 105 MPH $$ Forecaster Berg

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Post-Tropical Cyclone Karina Forecast Discussion Number 17

2020-09-17 04:37:58| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Wed Sep 16 2020 000 WTPZ41 KNHC 170237 TCDEP1 Post-Tropical Cyclone Karina Discussion Number 17 NWS National Hurricane Center Miami FL EP162020 Issued by NWS Central Pacific Hurricane Center Honolulu HI 800 PM PDT Wed Sep 16 2020 Karina has lacked deep convection for sufficiently long to be deemed a post-tropical cyclone, and this is the last NHC advisory. Satellite imagery shows a well-developed low cloud swirl that is estimated to be producing winds to 30 kt, primarily based on an earlier ASCAT pass. Karina is moving northwestward at 8 mph, and although a turn toward the west is expected the next day or so, it will remain over 23C waters. This will prevent the redevelopment of significant convection, and the cyclone is expected to gradually spin down until it becomes a trough and dissipates in a couple days. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 23.3N 125.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 12H 17/1200Z 23.7N 125.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 18/0000Z 23.9N 126.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 18/1200Z 23.8N 128.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 19/0000Z 23.5N 129.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 19/1200Z...DISSIPATED $$ Forecaster Birchard

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Tropical Storm Vicky Forecast Discussion Number 12

2020-09-17 04:34:08| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Wed Sep 16 2020 000 WTNT41 KNHC 170234 TCDAT1 Tropical Storm Vicky Discussion Number 12 NWS National Hurricane Center Miami FL AL212020 1100 PM AST Wed Sep 16 2020 A layer of cirrus clouds are covering the center of Vicky, but those clouds are associated with outflow from Hurricane Teddy. A combination of outflow from Teddy and an upper-level low to the north of Vicky is causing very strong westerly winds across the top of the struggling tropical storm. As a result, Vicky is producing minimal convection that is displaced to the east of the center. Recent ASCAT data indicated that the maximum winds are still near 35 kt, but Vicky's wind field is becoming smaller and the system is on the overall decline. There is no indication that the shear will decrease and Vicky should weaken as a result. The NHC forecast calls for Vicky to become a remnant low within 24 hours (if not sooner) and dissipate in a few days. Vicky is still heading generally westward. The tropical storm will likely continue westward through tomorrow morning, and then turn west-southwestward in the low-level tradewind flow after that for as long as it lasts. There is little spread in the track guidance and the NHC forecast is essentially the same as the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 21.6N 35.8W 35 KT 40 MPH 12H 17/1200Z 21.6N 37.1W 35 KT 40 MPH 24H 18/0000Z 21.0N 39.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 18/1200Z 20.2N 40.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 19/0000Z 19.4N 42.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 19/1200Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Depression Sally Forecast Discussion Number 24

2020-09-17 04:33:38| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Wed Sep 16 2020 000 WTNT44 KNHC 170233 TCDAT4 Tropical Depression Sally Discussion Number 24 NWS National Hurricane Center Miami FL AL192020 1000 PM CDT Wed Sep 16 2020 Although it remains a prodigious rain producer, surface observations indicate that Sally has weakened to a 30-kt depression over southeastern Alabama. The cyclone will continue to gradually spin down over the southeastern United States, and is likely to become a remnant low pressure system before merging with a frontal zone near North Carolina on Friday. The cyclone is moving northeastward near 8 kt. A northeastward to east-northeastward motion is expected over the next 36 hours or so as the system moves to the south of a broad trough over the northeastern United States. The official track forecast is about in the middle of the model guidance. KEY MESSAGES: 1. Significant and widespread flooding is expected across inland portions of Alabama, central Georgia and upstate South Carolina, and widespread flooding is possible across western/central North Carolina, and far southeast Virginia. Most widespread moderate to major river flooding will crest by the weekend, but rivers will remain elevated across southern Alabama and the Florida Panhandle. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 31.9N 86.1W 30 KT 35 MPH 12H 17/1200Z 32.7N 85.0W 30 KT 35 MPH...INLAND 24H 18/0000Z 34.0N 82.5W 25 KT 30 MPH...INLAND 36H 18/1200Z 35.0N 79.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 19/0000Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Teddy Forecast Discussion Number 18

2020-09-16 22:52:42| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Sep 16 2020 000 WTNT45 KNHC 162052 TCDAT5 Hurricane Teddy Discussion Number 18 NWS National Hurricane Center Miami FL AL202020 500 PM AST Wed Sep 16 2020 Recent satellite imagery is suggesting that Teddy is undergoing some westerly vertical wind shear, as indicated by outflow being more limited in the western portion of the circulation. The latest UW-CIMSS shear analysis suggests the magnitude of this shear could be about 10-15 kt, which could help to explain the lack of increase in organization of the cyclone today. The most recent Dvorak satellite intensity estimates provided CI values of 4.5-5.0, indicating that the initial intensity is still around 85 kt. The environmental conditions are not forecast to change much for Teddy over the next couple of days. The cyclone is forecast to move over warm waters within a somewhat dry atmospheric environment, while moderate shear is expected to continue due to an upper trough to its northwest. Based on these only somewhat favorable conditions for strengthening, along with what we have witnessed with the lack of intensification today, the NHC intensity forecast over the next few days is being lowered. Beyond day 3, there is evidence to suggest that Teddy may move over some cooler waters due to upwelling caused by Paulette. And, by day 4 global models are forecasting a further increase in vertical wind shear. These two factors should cause the cyclone to weaken late in the forecast period. This updated intensity forecast is in good agreement with the HFIP corrected consensus, HCCA. Teddy is moving northwestward at about 11 kt. This motion is forecast to continue for the next few days, as the cyclone is steered by a mid-level ridge to its north and northeast. Late in the forecast period, the portion of the ridge north of Teddy is expected to erode as a mid-latitude trough digs across the northeastern United States. This evolution should cause the cyclone to turn north-northwest and possibly north by day 5. The track guidance is tightly clustered through day 3, but increases quite a bit after that time, likely due to how the models are handling the approaching trough. The latest GFS delays a turn and shows a more westerly track, with the cyclone southwest of Bermuda by day 5, while the rest of the global models turn the system north sooner and take the system just east of Bermuda. The NHC track forecast is close to the previous one and is near the various multi-model track consensus aids. On the forecast track, Teddy could make a close to approach to Bermuda in about 5 days. However, based on the model spread at that time frame and average track error of about 200 n mi at 120 h, it is certainly too soon to know what impacts Teddy may have on the island. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 17.5N 50.8W 85 KT 100 MPH 12H 17/0600Z 18.6N 52.0W 90 KT 105 MPH 24H 17/1800Z 20.0N 53.4W 100 KT 115 MPH 36H 18/0600Z 21.5N 54.9W 105 KT 120 MPH 48H 18/1800Z 23.0N 56.3W 105 KT 120 MPH 60H 19/0600Z 24.8N 58.0W 100 KT 115 MPH 72H 19/1800Z 26.5N 60.2W 100 KT 115 MPH 96H 20/1800Z 29.5N 63.6W 90 KT 105 MPH 120H 21/1800Z 33.3N 64.6W 85 KT 100 MPH $$ Forecaster Latto

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