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Tropical Depression Rene Forecast Discussion Number 30

2020-09-14 16:51:27| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Mon Sep 14 2020 000 WTNT43 KNHC 141451 TCDAT3 Tropical Depression Rene Discussion Number 30 NWS National Hurricane Center Miami FL AL182020 1100 AM AST Mon Sep 14 2020 Deep convection continues to pulse over the eastern portion of Rene's circulation, enough to maintain the system's status as a tropical cyclone. However, recent visible statellite imagery suggest that the circulation may not be as well defined as it was yesterday. Satellite classifications support an initial wind speed of 25 kt. Strong west-northwesterly shear and dry air are expected to cause the depression to weaken and degenerate into a remnant low within the next 12-24 hours. The global models show the low-level circulation dissipating within 2 to 3 days and so does the official forecast. Rene has moved very little overnight but a west-southwestward or southwestward motion within the low-level steering flow should begin soon. That general motion is expected to continue until dissipation in a day or two. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 27.5N 48.3W 25 KT 30 MPH 12H 15/0000Z 27.0N 49.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 15/1200Z 26.4N 50.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 16/0000Z 25.5N 51.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 16/1200Z 24.6N 53.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 17/0000Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Vicky Forecast Discussion Number 2

2020-09-14 16:40:58| National Hurricane Center (Atlantic)

Issued at 200 PM CVT Mon Sep 14 2020 000 WTNT41 KNHC 141440 TCDAT1 Tropical Storm Vicky Discussion Number 2 NWS National Hurricane Center Miami FL AL212020 200 PM CVT Mon Sep 14 2020 A METOP A/B ASCAT scatterometer pass over the cyclone showed a large swath of winds in the northeast quadrant on the order of 35 to 39 kt. Deep convection in that region of the cyclone continues to increase as well as near the center of circulation. Accordingly, the initial intensity is raised to 40 kt, making this the twentieth named storm of the season. This should be a short-lived tropical cyclone, however, as increasing southwesterly shear is expected to quickly weaken Vicky to a depression in a couple days, and the system is expected to degenerate to a remnant low Thursday. This scenario is based on a combination of the global models and the ECMWF and FV3 SHIPS statistical-dynamical intensity models. The initial motion estimate is an uncertain 325/05 kt. The cyclone is forecast to move northwestward with some increase in forward speed during the next 24 hours within the low to mid-level steering flow produced by the eastern end of the African monsoon trough. By Tuesday night, Vicky should turn west-northwestward to westward along the southern periphery of a subtropical ridge over the eastern Atlantic. The official track forecast is close to the various consensus aids and is just to the north of the previous advisory beyond 36 hours. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 18.7N 28.5W 40 KT 45 MPH 12H 15/0000Z 19.6N 29.3W 40 KT 45 MPH 24H 15/1200Z 20.6N 30.5W 35 KT 40 MPH 36H 16/0000Z 21.6N 32.4W 35 KT 40 MPH 48H 16/1200Z 22.2N 34.6W 30 KT 35 MPH 60H 17/0000Z 22.7N 36.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 17/1200Z 23.0N 39.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 18/1200Z 23.1N 42.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 19/1200Z...DISSIPATED $$ Forecaster Roberts

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Tropical Storm Karina Forecast Discussion Number 7

2020-09-14 16:37:29| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Mon Sep 14 2020 000 WTPZ41 KNHC 141437 TCDEP1 Tropical Storm Karina Discussion Number 7 NWS National Hurricane Center Miami FL EP162020 800 AM PDT Mon Sep 14 2020 There has been little change to the appearance of Karina over the past several hours, with a large area of deep convection remaining displaced mostly to the southwest of the center due to moderate northeasterly shear. Because the general appearance of the cyclone is unchanged, the initial intensity remains 40 kt based on earlier ASCAT data. The shear is expected to slowly relax over the next 24 h while the system remains over relatively warm waters, and some slight strengthening is possible during that time. After 24 h, Karina is forecast to cross the 26 degrees C SST isotherm and begin to enter a drier, more stable atmospheric environment. These factors should cause Karina to steadily weaken beginning by late Tuesday. By 72 h, the cyclone should be over water temperatures of less than 24C, and the system is expected to degenerate to a remnant low by 96 h, if not sooner. The low is then forecast to dissipate by day 5. The NHC intensity forecast is unchanged from the previous one, and is in good agreement with the various multi-model consensus aids. Karina has resumed a northwestward movement, and the initial motion is 305/7 kt. A northwestward motion is expected to continue while the deep convection persists, as the cyclone is steered by a mid-level ridge to its north and northeast. Once the cyclone has weakened and lost most of its convection, it is expected to turn toward the west under the influence of the low-level flow. The track guidance has shifted northward at most time frames, and the latest NHC track forecast has been adjusted to the right as well, but is still to the south of most of the track guidance. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 18.1N 118.5W 40 KT 45 MPH 12H 15/0000Z 18.8N 119.4W 45 KT 50 MPH 24H 15/1200Z 20.0N 120.9W 45 KT 50 MPH 36H 16/0000Z 21.2N 122.4W 40 KT 45 MPH 48H 16/1200Z 22.3N 123.8W 35 KT 40 MPH 60H 17/0000Z 23.2N 125.2W 30 KT 35 MPH 72H 17/1200Z 23.7N 126.2W 30 KT 35 MPH 96H 18/1200Z 23.7N 127.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 19/1200Z...DISSIPATED $$ Forecaster Latto

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Tropical Storm Sally Forecast Discussion Number 11

2020-09-14 11:55:25| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Mon Sep 14 2020 000 WTNT44 KNHC 140954 CCA TCDAT4 Tropical Storm Sally Discussion Number 11...Corrected NWS National Hurricane Center Miami FL AL192020 400 AM CDT Mon Sep 14 2020 Corrected 4th Key Message The organization of Sally hasn't changed much during the past several hours. While there was a large burst of convection earlier, it did not translate into any intensification, with flight-level reconnaissance and SFMR surface winds still supporting an initial wind speed of 50 kt. The Air Force Reserve plane did find that the size of tropical-storm-force wind field has notable grown to the north and northwest of the center. The storm still has time to intensify under a seemingly conducive environment during the next 24-36 hours, before a combination of increasing westerly wind shear and land interaction will probably slow the intensification rate. Model guidance has come down slightly from 6 hours ago, but it has been inconsistent from cycle to cycle. The new intensity forecast is similar to the previous one and lies near the top end of the guidance envelope. The reconnaissance plane showed that Sally took a westward turn during the past several hours, but the storm appears to have a resumed a more west-northwestward motion recently. Weak ridging over the southern United States is expected to cause this general motion with a decrease in forward speed today before the storm slowly turns northward sometime on Tuesday due to an approaching trough. Guidance is not in good agreement on exactly when that turn occurs, causing a good deal of spread for a relatively short-range forecast. The track forecast has been shifted to the left in the short-term primarily due to the initial position, showing a track near or over extreme southeastern Louisiana, then is the near the previous one at its final landfall. The bottom line continues to be that Sally is expected to be a dangerous slow-moving hurricane near the coast of southeastern Louisiana, Mississippi and Alabama during the next 2-3 days. KEY MESSAGES: 1. It is too early to determine where Sally's center will move onshore given the uncertainty in the timing and location of Sally's northward turn near the central Gulf Coast. Users should not focus on the details of the official forecast track, since NHC's average forecast error at 48 hours is around 80 miles, and dangerous storm surge, rainfall, and wind hazards will extend well away from the center. 2. An extremely dangerous and life-threatening storm surge is expected for areas outside the southeastern Louisiana Hurricane and Storm Damage Risk Reduction System from Port Fourchon, Louisiana, to the Alabama/Florida border, where a Storm Surge Warning is in effect. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are expected by late today within portions of the Hurricane Warning area from Morgan City, Louisiana, to the Mississippi/Alabama border, including Metropolitan New Orleans, with tropical storm conditions likely to begin by late this morning. Preparations should be rushed to completion in those areas. 4. Sally may continue to produce flash flooding across the Florida peninsula and prolong existing minor river flooding across west-central Florida through today. Life-threatening flash flooding is possible and widespread minor to isolated major flooding on area rivers is likely along and just inland of the Central Gulf Coast. Significant flash and urban flooding, as well as widespread minor to moderate river flooding is likely across Mississippi and Alabama through the middle of the week. Flooding impacts are expected to spread farther across the Southeast through the week. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 28.3N 87.3W 50 KT 60 MPH 12H 14/1800Z 28.6N 88.1W 60 KT 70 MPH 24H 15/0600Z 29.1N 88.9W 70 KT 80 MPH 36H 15/1800Z 29.7N 89.3W 75 KT 85 MPH 48H 16/0600Z 30.6N 89.2W 60 KT 70 MPH...INLAND 60H 16/1800Z 31.6N 88.6W 30 KT 35 MPH...INLAND 72H 17/0600Z 32.5N 87.6W 25 KT 30 MPH...INLAND 96H 18/0600Z 33.5N 85.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 19/0600Z...DISSIPATED $$ Forecaster Blake

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Tropical Depression Twenty-one Forecast Discussion Number 1

2020-09-14 11:50:27| National Hurricane Center (Atlantic)

Issued at 900 AM CVT Mon Sep 14 2020 000 WTNT41 KNHC 140950 TCDAT1 Tropical Depression Twenty-One Special Discussion Number 1 NWS National Hurricane Center Miami FL AL212020 900 AM CVT Mon Sep 14 2020 First-light visible satellite imagery indicates that the low pressure system that moved off the coast of Africa a few days ago has continued to become better organized overnight. Scatterometer surface wind data from around 13/2200 UTC indicated that the circulation had become better defined, and that surface winds of 25-28 kt existed in the southwestern quadrant. Since then, deep convection has increased, and it is presumed that the surface winds and circulation definition have increased in response, which justifies the initiation of advisories on TD-21. The initial motion estimate is an uncertain 355/05 kt. The cyclone is forecast to gradually move northward today and northwestward tonight as the depression moves around the eastern end of the eastern Atlantic/west African monsoon trough. By Tuesday night and continuing into Wednesday and Thursday, a west-northwestward to westward motion along the southern periphery of a deep-layer ridge is expected. The NHC track forecast lies down the middle of the surprisingly tightly packed guidance envelope, and is similar to the consensus model TVCA. The depression is expected to be short-lived as a tropical cyclone. Having said that, there is a narrow window of opportunity today and tonight for the cyclone to strengthen into a tropical storm before strong westerly shear in excess of 30 kt is forecast to induce rapid weakening on Tuesday. The cyclone is expected to degenerate into a remnant low by Tuesday night, and then dissipate over water on Friday, if not sooner. FORECAST POSITIONS AND MAX WINDS INIT 14/1000Z 18.5N 28.3W 30 KT 35 MPH 12H 14/1800Z 19.6N 28.6W 35 KT 40 MPH 24H 15/0600Z 20.5N 29.6W 30 KT 35 MPH 36H 15/1800Z 21.3N 30.9W 25 KT 30 MPH 48H 16/0600Z 21.9N 32.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 16/1800Z 22.4N 34.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 17/0600Z 22.8N 36.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 18/0600Z 23.4N 41.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 19/0600Z...DISSIPATED $$ Forecaster Stewart/Beven

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