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Hurricane Paulette Forecast Discussion Number 36

2020-09-15 22:35:47| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 15 2020 000 WTNT42 KNHC 152035 TCDAT2 Hurricane Paulette Discussion Number 36 NWS National Hurricane Center Miami FL AL172020 500 PM AST Tue Sep 15 2020 Another fortuitous AMSR2 microwave pass over the cyclone showed the outer concentric ring open over the south semicircle and a more noticeable vertical tilt. Furthermore, the cloud tops associated with the deep convection in the north quadrant have warmed during the past several hours. Consequently, the initial intensity is lowered to 85 kt and is in best agreement with the subjective and objective satellite intensity estimates. Paulette continues to lose its tropical characteristics as it mingles with the rapidly approaching baroclinic zone from the northwest. In fact, earlier successive METOP A and B scatterometer passes on Paulette revealed that the northwest quadrant 34-kt wind radii had nearly doubled in size due to the aforementioned invading frontal zone moving out of the Canadian Maritimes. The sea surface temperatures quickly decrease to less than 20C within 24 hours as Paulette accelerates east-northeastward. As a result, the cyclone should weaken rather quickly and complete its extratropical transition on Thursday, as indicated in the global models and the statistical-dynamical guidance. Paulette is moving east-northeastward, or 060/26 kt, and this motion should continue with a further increase in forward speed through Thursday. Toward the end of the week, the cyclone will likely turn south-southeastward to southward as it moves within the western peripheral flow of a mid- to upper tropospheric cut off low to the east of the cyclone. The NHC track forecast is basically an update of the previous advisory and is based on the various consensus guidance. The initial wind radii and subsequent forecast wind radii were adjusted based on METOP A/B ASCAT 1110 UTC and 1424 UTC scatterometer passes. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 39.5N 55.0W 85 KT 100 MPH 12H 16/0600Z 41.4N 50.1W 80 KT 90 MPH 24H 16/1800Z 44.0N 42.9W 70 KT 80 MPH 36H 17/0600Z 45.8N 36.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 17/1800Z 45.8N 33.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 60H 18/0600Z 43.9N 32.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 18/1800Z 41.2N 32.8W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 19/1800Z 38.0N 32.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 20/1800Z 34.5N 32.3W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts

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Tropical Storm Vicky Forecast Discussion Number 7

2020-09-15 22:33:44| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 15 2020 000 WTNT41 KNHC 152033 TCDAT1 Tropical Storm Vicky Discussion Number 7 NWS National Hurricane Center Miami FL AL212020 500 PM AST Tue Sep 15 2020 Vicky continues to be blasted by around 50 kt of westerly shear, with deep convection being continually removed from the center. Overall the coverage and intensity of the deep convection has decreased since this morning, and the initial intensity has been set to 40 kt based on a blend of the latest Dvorak estimates (30-35 kt) and SATCON (45 kt). The high shear is expected to persist, and that in combination with marginal SSTs should result in weakening, and Vicky is expected to become a remnant low in around 36 hours, with dissipation expected in about 3 days. The new NHC intensity forecast is close to HCCA and the IVCN consensus aids. The initial motion estimate is a bit faster toward the west-northwest or 300/10. Vicky should continue west-northwestward for the next 12 to 24 hours and then turn westward in the low-level flow before dissipation. The new NHC track forecast is similar to the previous one, near the middle of the guidance envelope, and has been adjusted a bit slower toward the latest consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 21.2N 32.1W 40 KT 45 MPH 12H 16/0600Z 21.6N 33.4W 35 KT 40 MPH 24H 16/1800Z 22.1N 35.2W 30 KT 35 MPH 36H 17/0600Z 22.4N 37.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 17/1800Z 22.4N 38.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 18/0600Z 22.2N 40.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 18/1800Z...DISSIPATED $$ Forecaster Brennan

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Hurricane Sally Forecast Discussion Number 17

2020-09-15 16:46:01| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Tue Sep 15 2020 000 WTNT44 KNHC 151445 TCDAT4 Hurricane Sally Discussion Number 17 NWS National Hurricane Center Miami FL AL192020 1000 AM CDT Tue Sep 15 2020 The satellite presentation of Sally has not changed much since overnight. A ragged eye is seen in WSR-88D radar imagery, with a band occasionally trying to wrap around the southwestern side. A NOAA reconnaissance aircraft has just recently provided a new center fix, and data from the center drop indicated the minimum pressure is 983 mb. The first pass through the northeastern quadrant suggests that the 50-kt wind field may have expanded, but there has been little change in peak winds reported by the aircraft. The intensity has been held at 75 kt pending additional data from the NOAA P-3 mission that has just begun. A highly elevated oil rig just northeast of the center reported peak has reported sustained winds of 69 kt with a gust to 86 kt around 1200 UTC this morning. Sally has been meandering this morning, but the longer-term motion is northwestward or 315/2 kt. Sally remains within an area of weak steering flow, but a weak mid-level trough over the south-central United States is forecast to slide eastward over the next over the next couple of days. This pattern should cause Sally to move very slowly north-northwestward to northward over the next 24 hours, with the center of the hurricane nearing the northern Gulf Coast late tonight or Wednesday. By late Wednesday, Sally should turn northeastward as the aforementioned trough approaches Missouri and Arkansas. The new forecast has been nudged slightly eastward in the early portion of the track forecast, but the latter portion is very close to the previous advisory. The new track lies a little to the west of the various consensus aids in deference to the typically reliable GFS and ECMWF models that are near the left edge of the guidance envelope. Sally's forward motion is forecast to be around 5 kt or less throughout the forecast period, which will result in a long period of heavy rainfall and historic flooding along the north-central Gulf Coast. Moderate westerly shear and upwelling beneath the slow moving hurricane are likely to prevent strengthening today. The shear is forecast to increase tonight and although some slight weakening could occur before the center reaches the coast, Sally is predicted to remain a dangerous hurricane through landfall. Once Sally moves inland, rapid weakening is expected and circulation is forecast to lose definition and dissipate by day 4. Users are reminded to not focus on the specific timing and location of landfall. Life-threatening storm surge, historic flash flooding from heavy rainfall, and dangerous winds will affect a large portion of the north-central Gulf Coast during the next few days. KEY MESSAGES: 1. Life-threatening storm surge is expected from the Mouth of the Mississippi River to the Okaloosa/Walton County Line in the Florida Panhandle. The highest inundation is expected along the Alabama coast, including Mobile Bay. 2. Historic life-threatening flash flooding is likely through Wednesday along and just inland of the coast from the western Florida Panhandle to far southeastern Mississippi. Widespread moderate to major river flooding is forecast along and just inland of the central Gulf Coast. Significant flash and urban flooding, as well as widespread minor to moderate river flooding, are likely across inland portions of Mississippi, Alabama, northern Georgia, and the western Carolinas through the week. 3. Hurricane conditions are expected today within portions of the Hurricane Warning area along the Mississippi and Alabama coastlines and the western Florida Panhandle. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 29.1N 88.2W 75 KT 85 MPH 12H 16/0000Z 29.6N 88.2W 75 KT 85 MPH 24H 16/1200Z 30.2N 88.1W 70 KT 80 MPH 36H 17/0000Z 31.0N 87.6W 55 KT 65 MPH...INLAND 48H 17/1200Z 31.9N 86.6W 35 KT 40 MPH...INLAND 60H 18/0000Z 32.6N 85.2W 25 KT 30 MPH...INLAND 72H 18/1200Z 33.0N 83.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/1200Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Vicky Forecast Discussion Number 6

2020-09-15 16:39:57| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 15 2020 000 WTNT41 KNHC 151439 TCDAT1 Tropical Storm Vicky Discussion Number 6 NWS National Hurricane Center Miami FL AL212020 1100 AM AST Tue Sep 15 2020 Although the stiff westerly shear (magnitude of greater than 50 kt) continues to affect Vicky's vertical structure this morning, a 1107 UTC METOP-B scatterometer pass indicated that the cyclone is maintaining 45-kt sustained winds well to the east-northeast of the center. Therefore, once again for this advisory, the initial intensity is held at 45 kt. The ECMWF/FV3 SHIPS intensity models and the deterministic guidance, including the simulated infrared imagery product, agree with Vicky weakening to a remnant low in 36 hours and dissipating by 72 hours due to the persistent strong shear. The initial motion is estimated to be west-northwestward, or 295/8 kt. Vicky is forecast to continue on this general motion through Wednesday night within the low-level tradewind flow. No significant changes were made to the previous advisory, and the new NHC forecast is based on the HCCA and TVCA consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 20.6N 31.0W 45 KT 50 MPH 12H 16/0000Z 21.3N 32.1W 40 KT 45 MPH 24H 16/1200Z 21.9N 34.0W 35 KT 40 MPH 36H 17/0000Z 22.3N 36.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 17/1200Z 22.2N 38.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 18/0000Z 22.2N 39.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 18/1200Z...DISSIPATED $$ Forecaster Roberts

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Hurricane Paulette Forecast Discussion Number 35

2020-09-15 16:38:02| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 15 2020 000 WTNT42 KNHC 151437 TCDAT2 Hurricane Paulette Discussion Number 35 NWS National Hurricane Center Miami FL AL172020 1100 AM AST Tue Sep 15 2020 A 0533 UTC AMSR2 overpass on Paulette already reveals structural changes associated with the approaching mid-latitude baroclinic zone. The microwave image and GOES-16 mid- to upper-level water vapor imagery show drier more stable air beginning to intrude into the western portion of the cyclone. Additionally, Paulette's rain shield is more confined to the northern half of the system, while drying out in the southern semi-circle. Only fragments of the eyewall remain in that particular area. The initial intensity is held at 90 kt for this advisory and is supported by the subjective satellite intensity estimate T-numbers from TAFB and SAB. Although Paulette is beginning to lose some of its tropical characteristics, the cyclone still has a small window of opportunity to strengthen while it continues moving over warm sea surface temperatures during the next 12-18 hrs. Afterward, the water temperature drop drastically to less than 20C while Paulette becomes more involved with the aforementioned baroclinic system. As a result, the cyclone should weaken rather rapidly and complete its extratropical transition on Thursday, and this is based on an agreement of the large-scale models and the statistical-dynamical guidance. The aforementioned microwave pass indicated that the center of circulation was a bit west-southwest of the previous position and therefore the initial estimated motion is believed to be northeastward, or 055/25 kt. Paulette is forecast to accelerate further and turn east-northeastward later tonight and continuing through Wednesday night, then slow down a bit on Thursday. Toward the end of the week, the cyclone will likely turn east- southeastward to south-southeastward as it moves within the western peripheral flow of a mid- to upper tropospheric cut off low to the east of the cyclone. The NHC track forecast is just a little faster than the previous one through 60 hours and lies closer to the HFIP Corrected Consensus Approach model and is also similar to the GFEX ECMWF/FV3 simple consensus. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 38.3N 57.9W 90 KT 105 MPH 12H 16/0000Z 40.1N 53.6W 95 KT 110 MPH 24H 16/1200Z 42.7N 46.8W 85 KT 100 MPH 36H 17/0000Z 45.0N 40.1W 70 KT 80 MPH 48H 17/1200Z 46.2N 35.7W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 18/0000Z 45.6N 33.9W 45 KT 50 MPH...POST-TROP/EXTRATROP 72H 18/1200Z 43.9N 33.3W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 19/1200Z 39.9N 32.2W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 20/1200Z 37.0N 31.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts

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