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Hurricane Leslie Forecast Discussion Number 65

2018-10-12 16:38:48| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Fri Oct 12 2018 000 WTNT43 KNHC 121438 TCDAT3 Hurricane Leslie Discussion Number 65 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Fri Oct 12 2018 Leslie's cloud pattern continues to feature a central dense overcast, but with only hints of an eye in visible imagery. A partial northern eyewall was noted on a 0910Z SSMIS overpass. Dvorak intensity estimates have decreased slightly, and based on this, the initial intensity has been conservatively nudged down to 75 kt. The wind field is quite large, especially south of the center, as confirmed by a pair of recent ASCAT passes, and the initial wind radii have been adjusted using those data. The initial motion estimate is now 070/28. Leslie is moving quickly east-northeastward on the southern side of a powerful longwave trough centered over the north Atlantic. The track forecast reasoning has changed since the last advisory, with the GFS, ECMWF, and now the 06Z run of the UKMET all showing a more eastward motion of Leslie toward the Iberian Peninsula as the cyclone is picked up by the aforementioned trough. The new NHC track forecast has been adjusted significantly to the north and east, especially beyond 24 hours, but still lies to the south of and is slower than the GFS and ECMWF. Once the system moves inland, the low-level center should dissipate over the high terrain, but a 72 hour remnant low point is included for continuity purposes. Needless to say, confidence in the official track forecast beyond 24 hours is quite low given the recent shift in the models, and further adjustments will likely be necessary. The intensity forecast shows Leslie only slowly weakening as a tropical cyclone during the next 24 hours due to a combination of cool SSTs and increasing shear from the trough. However, simulated satellite imagery and model fields suggest that Leslie will transition to a powerful post-tropical cyclone by 36 hours, likely still at hurricane intensity as shown by the global models. Weakening is expected after the trough passes Leslie by, and the mid-level circulation will likely be sheared away by strong upper-level winds. Leslie is expected to bring significant rain and wind impacts to portions of Portugal and Spain by Sunday, and residents in those areas should refer to products from their local meteorological services for more information on these hazards. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 33.0N 28.0W 75 KT 85 MPH 12H 13/0000Z 34.2N 23.0W 70 KT 80 MPH 24H 13/1200Z 35.4N 17.0W 65 KT 75 MPH 36H 14/0000Z 36.0N 12.5W 65 KT 75 MPH...POST-TROPICAL 48H 14/1200Z 36.3N 9.1W 50 KT 60 MPH...POST-TROPICAL 72H 15/1200Z 37.0N 4.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 16/1200Z...DISSIPATED $$ Forecaster Brennan

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Hurricane Leslie Forecast Discussion Number 64

2018-10-12 11:11:23| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Oct 12 2018 000 WTNT43 KNHC 120911 TCDAT3 Hurricane Leslie Discussion Number 64 NWS National Hurricane Center Miami FL AL132018 500 AM AST Fri Oct 12 2018 Leslie has changed little in organization since the last advisory. The eye is currently not apparent in conventional satellite imagery, although recent microwave overpasses indicate at least a partial eyewall is present under the overcast. Satellite intensity estimates have changed little, so the initial intensity is held at 80 kt. The initial motion is now 065/24. The guidance is in good agreement that this general motion should continue for 24 h or so. After that, there is a major model divergence. The GFS, ECMWF, and the various consensus models now show a continued east-northeast motion until landfall in Portugal or Spain. On the other hand, the UKMET, UK ensemble mean, and Canadian models show a turn toward the south and then back to the west. Since the previous forecast showed a southward and westward turn, the new forecast track will also follow this scenario. However, it is shifted well to the east of the previous track due to the forecasts of the other models. Needless to say, the latter portion of the track forecast is low confidence. Leslie should gradually weaken as it approaches Madeira Island during the next 24-36 h. After that, the intensity forecast is dependent on what track the cyclone takes. If it follows the GFS/ECMWF scenario, the system would likely make landfall on the Iberian peninsula and quickly dissipate. If it follows the UKMET scenario, a combination of shear, cool water, and dry air entrainment should cause weakening. Since the track forecast is closer to the UKMET scenario, the intensity forecast follows the previous forecast in having Leslie decay to a post-tropical low by 72 h. However, this is also a low confidence forecast due to the uncertainties in the track forecast. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 31.9N 31.0W 80 KT 90 MPH 12H 12/1800Z 33.1N 26.5W 80 KT 90 MPH 24H 13/0600Z 34.2N 20.3W 75 KT 85 MPH 36H 13/1800Z 34.6N 15.5W 65 KT 75 MPH 48H 14/0600Z 34.0N 13.0W 50 KT 60 MPH 72H 15/0600Z 32.0N 12.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 16/0600Z 30.0N 13.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 17/0600Z 28.0N 18.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Tropical Storm Sergio Forecast Discussion Number 52

2018-10-12 10:55:50| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Fri Oct 12 2018 000 WTPZ41 KNHC 120855 TCDEP1 Tropical Storm Sergio Discussion Number 52 NWS National Hurricane Center Miami FL EP212018 300 AM MDT Fri Oct 12 2018 Sergio's cloud shield is well separated from the poorly organized surface circulation and is confined to the northwest quadrant. Subjective satellite intensity estimates yield a reduction in the initial intensity to 45 kt for this advisory. Weakening should continue this morning due to cool oceanic sea surface temperatures and belligerent southwesterly shear, but Sergio is still expected to be a tropical storm as it make landfall in the Pacific coast of Baja California Sur. Afterward, Sergio should quickly become a depression and eventually dissipate as it traverses the rugged terrain of the northwestern Mexico state of Sonora. The initial motion is estimated to be northeastward, or 045/21 kt, within the deep-layer southwesterly flow produced by a mid-latitude trough situated just west of the California coast. This synoptic steering pattern should steer Sergio toward the northeast at an accelerated rate of speed. A 36 hour post-tropical/remnant low point is maintained to simply represent the inland motion of Sergio. The NHC forecast lies in the middle of the various multi-model consensus aids, and is basically an update of the previous package. The primary threat associated with Sergio and its remnants continues to be life-threatening flash flooding and mudslides within mountainous terrain in the Mexico states of Baja California Sur, Sonora, the U.S. Southern Plains, and Arkansas through the weekend. For more information about this potential hazard, see products from the Weather Prediction Center and your local weather forecast office. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 26.1N 113.8W 45 KT 50 MPH 12H 12/1800Z 28.2N 111.2W 30 KT 35 MPH...INLAND 24H 13/0600Z 31.0N 107.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 13/1800Z 33.8N 103.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 48H 14/0600Z...DISSIPATED $$ Forecaster Roberts

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Post-Tropical Cyclone Michael Forecast Discussion Number 23

2018-10-12 10:48:47| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Fri Oct 12 2018 000 WTNT44 KNHC 120848 TCDAT4 Post-Tropical Cyclone Michael Discussion Number 23 NWS National Hurricane Center Miami FL AL142018 500 AM EDT Fri Oct 12 2018 Satellite imagery and surface observations indicate that Michael has become a storm-force extratropical low as it moves off of the coast of the United States. The initial intensity has been increased to 55 kt based on the surface observations, and some additional increase in strength is expected during the next 12-24 h. After that time, the cyclone should gradually weaken, and it is forecast to dissipate over the eastern Atlantic by 96 h. The revised intensity and size forecast are based mainly on the guidance from the Ocean Prediction Center. The initial motion is 065/25. The cyclone should move very rapidly toward the east-northeast, followed by a more eastward motion near the end of the cyclone's life. This is the last public advisory issued by the National Hurricane Center on this system. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and available on the Web at https://ocean.weather.gov/shtml/NFDHSFAT1.shtml. Additional information on the remaining impacts over the United States can be found in products issued by local National Weather Service forecast offices. Key Messages: 1. Heavy rainfall may lead to flash flooding this morning from eastern New Jersey to southern New England. Elsewhere high water, flooding, and flash flooding may persist today where heavy rain fell very recently in the Carolinas and Mid-Atlantic states. 2. Gale-force winds will continue for a few more hours over portions of southeastern Virginia, the southern Chesapeake Bay, and the Delmarva Peninsula. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 38.0N 73.1W 55 KT 65 MPH...POST-TROP/EXTRATROP 12H 12/1800Z 40.4N 66.8W 60 KT 70 MPH...POST-TROP/EXTRATROP 24H 13/0600Z 43.8N 55.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 13/1800Z 46.2N 42.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 14/0600Z 47.0N 28.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 15/0600Z 46.0N 11.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 96H 16/0600Z...DISSIPATED $$ Forecaster Beven

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Tropical Storm Nadine Forecast Discussion Number 13

2018-10-12 10:46:49| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Oct 12 2018 000 WTNT45 KNHC 120846 TCDAT5 Tropical Storm Nadine Discussion Number 13 NWS National Hurricane Center Miami FL AL152018 500 AM AST Fri Oct 12 2018 A 0353 UTC AMSR-2 microwave overpass and GOES-16 shortwave infrared imagery show that the 30-40 kt of west-southwesterly shear, depicted in the UW-CIMSS shear analysis, is partially exposing, or decoupling, Nadine's surface circulation from the convective mass. The cloud pattern, however, hasn't changed during the past 6 hours and in fact, the cloud top temperatures in the curved band over the north semicircle have decreased somewhat. TAFB and SAB satellite intensity estimates remained unchanged, and the initial intensity is held at 45 kt. The Decay SHIPS statistical intensity model indicates that the shear will persist and increase a little more which should cause Nadine to spin down and dissipate in 48 hours, or possibly sooner. The large-scale models all show the cyclone opening up into a trough of low pressure and ultimately dissipating over the deep tropical central Atlantic at that time. The official forecast follows suit and is an update of the previous advisory. The initial motion is estimated to be west-northwestward, or 295/7 kt. A low to mid-level ridge anchored between Nadine to the south and Hurricane Leslie to the north, should steer the cyclone west-northwestward and then westward at an accelerated pace until dissipation. The NHC forecast has again been adjusted a little south and toward both the NOAA-HCCA and TVCN consensus models. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 15.2N 35.5W 45 KT 50 MPH 12H 12/1800Z 15.4N 37.2W 40 KT 45 MPH 24H 13/0600Z 15.6N 39.7W 30 KT 35 MPH 36H 13/1800Z 15.8N 42.7W 30 KT 35 MPH 48H 14/0600Z...DISSIPATED $$ Forecaster Roberts

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