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Tropical Storm Leslie Forecast Discussion Number 51

2018-10-09 04:40:19| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Oct 08 2018 000 WTNT43 KNHC 090240 TCDAT3 Tropical Storm Leslie Discussion Number 51 NWS National Hurricane Center Miami FL AL132018 1100 PM AST Mon Oct 08 2018 Satellite and microwave data show that Leslie continues to have a small central dense overcast, with the latest microwave images suggesting that Leslie is forming a mid-level eye. Although deep convection has recently decreased somewhat, all of the 00Z intensity estimates were 55 kt or higher, so the wind speed is set to that value. There is no significant change in initial motion- still southeastward at about 12 kt. Leslie should slow down and turn toward the south-southeast during the next day or two as the cyclone becomes steered by a mid-level ridge over the central Atlantic. A new trough moves into the eastern Atlantic after that time, which should eject Leslie generally east-northeastward to the south of the Azores. Models continue to be in poor agreement on whether that trough will accelerate Leslie quickly to the northeast at long range or drop the cyclone to the southwest of Portugal. The recent GFS-based guidance has generally shifted southward and is slower, more in line with the 12Z UK/ECMWF models. The new NHC forecast follows that trend, but is still on the northern side of the consensus due to continuity concerns, and additional southward adjustments could be required on later advisories. Leslie is forecast to move across marginally warm waters within a moderate shear but a more moist environment over the next few days. These conditions are likely to support slow strengthening, and model guidance is in general agreement on this scenario. Only minor adjustments were made to the previous forecast, and the NHC forecast remains between the intensity consensus and corrected- consensus aids. By day 5, increasing shear and cold waters should weaken Leslie, and it will probably lose convection to transition into a post-tropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 32.9N 44.6W 55 KT 65 MPH 12H 09/1200Z 31.5N 43.3W 55 KT 65 MPH 24H 10/0000Z 29.6N 42.5W 60 KT 70 MPH 36H 10/1200Z 28.1N 42.1W 60 KT 70 MPH 48H 11/0000Z 27.9N 41.2W 65 KT 75 MPH 72H 12/0000Z 30.0N 35.5W 75 KT 85 MPH 96H 13/0000Z 33.5N 24.5W 70 KT 80 MPH 120H 14/0000Z 35.5N 16.0W 55 KT 65 MPH...POST-TROPICAL $$ Forecaster Blake

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Tropical Storm Leslie Forecast Discussion Number 50

2018-10-08 22:48:22| National Hurricane Center (Atlantic)

Issued at 500 PM AST Mon Oct 08 2018 000 WTNT43 KNHC 082048 TCDAT3 Tropical Storm Leslie Discussion Number 50 NWS National Hurricane Center Miami FL AL132018 500 PM AST Mon Oct 08 2018 GOES-16 data indicate that Leslie has a small central dense overcast with an inner core trying to form on the last few visible images. Convection has also deepened somewhat, and the overall cloud pattern is becoming more symmetric. All signs point to strengthening and the Dvorak estimates are increasing. So for Leslie's 50th advisory, the wind speed is raised to 50 kt, near the CIMSS ADT value. Leslie is moving southeastward at about 12 kt; an unusually fast pace for this direction. The storm is forecast to slow down somewhat and turn toward the south-southeast during the next day or two as the cyclone separates from the mid-latitude flow temporarily and becomes steered by a mid-level ridge over the central Atlantic. Fortunately the ridge isn't strong enough for Leslie to move westward again, and the models all eject Leslie northeastward because of a deepening trough over the eastern Atlantic. There has been a notable trend southward through 48 hours, and the official forecast follows that idea. The forecast becomes a nightmare at long range, however, with very little agreement on whether Leslie is accelerated ahead of the trough, like the latest FV3GFS, or gets left behind again, like the ECMWF. These differences result in a 1200 mile spread of the historically reliable models by day 5, resulting in a very low confidence forecast. The bulk of the guidance is now indicating that the "left behind" option is becoming more likely, but continuity dictates making forecast changes in smaller chunks. So the official forecast is much slower and farther south at long range, but is well north of the latest model consensus. Further southward adjustments could be required if model trends continue. Interestingly, model guidance is becoming more certain on Leslie becoming a hurricane again as it moves over warmer (but still marginally warm) waters, into a lighter-shear and higher mid-level humidity enviroment. This makes some sense given that the track is shifting southward and Leslie should finally move over a warmer portion of the subtropical Atlantic that it hasn't touched yet. Thus the intensity forecast is higher than the previous one, and the corrected-consensus models even suggest category 2 as a peak intensity is possible. By day 5, increasing shear and cooler waters should weaken Leslie, and it could be undergoing extratropical transition at that time. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 33.8N 45.8W 50 KT 60 MPH 12H 09/0600Z 32.5N 44.4W 55 KT 65 MPH 24H 09/1800Z 30.6N 43.2W 55 KT 65 MPH 36H 10/0600Z 28.9N 42.5W 60 KT 70 MPH 48H 10/1800Z 28.2N 41.7W 65 KT 75 MPH 72H 11/1800Z 29.5N 37.0W 75 KT 85 MPH 96H 12/1800Z 33.5N 26.5W 75 KT 85 MPH 120H 13/1800Z 37.0N 17.0W 60 KT 70 MPH $$ Forecaster Blake

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Hurricane Michael Forecast Discussion Number 9

2018-10-08 22:41:49| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Mon Oct 08 2018 000 WTNT44 KNHC 082041 TCDAT4 Hurricane Michael Discussion Number 9 NWS National Hurricane Center Miami FL AL142018 400 PM CDT Mon Oct 08 2018 Data from an Air Force Reserve hurricane hunter aircraft that was in the storm until about 1700 UTC continued to indicate that the hurricane was deepening. The pressure had fallen to 978 mb on the final fix, but the aircraft was still not able to sample the northeastern portion of the storm due to the close proximity of land. The initial intensity has been increased to 70 kt based on a blend of Dvorak satellite classifications and the continued deepening that was observed. The upper-level outflow has gradually improved over Michael but it is still somewhat restricted over the western portion of the storm. There has been no significant change to the intensity forecast thinking. The moderate shear that has been affecting the cyclone is not expected to prevent strengthening while Michael moves over the warm waters of the eastern Gulf of Mexico. Although the statistical guidance is somewhat lower this cycle, the regional hurricane and global models still favor steady to rapid strengthening, and the NHC forecast is closest to the Florida State Superensemble and the HFIP corrected consensus model. Aircraft and satellite fixes show that Michael has been wobbling as it moves generally northward. Smoothing through the wobbles gives a long-term initial motion estimate of 355/8 kt. Michael is forecast to move north-northwestward to northward between a deep-layer ridge over the western Atlantic and a trough over the west-central United States. The trough is forecast move eastward, causing Michael to turn northeastward in 36 to 48 hours, and the cyclone should then accelerate northeastward as it enters the mid-latitude westerly flow. The 1200 UTC dynamical models have converged on both the track and forward speed through the first 48 to 72 hours. The updated NHC track has been nudged slightly westward through 48 hours to be closer to the latest consensus aids. It should be noted that the location and magnitude of peak storm surge flooding is very sensitive to small changes in the track, intensity, and structure of the hurricane. Since there is still uncertainty in all of these parameters, the official NHC storm surge forecast and watch/warning areas includes various plausible scenarios. Regardless of the eventual track and intensity of Michael, life-threatening storm surge inundation is expected along portions of the Florida Panhandle and Big Bend/Nature Coast, and the storm surge watch has been upgraded to a storm surge warning for parts of this area. The NOAA G-IV aircraft is conducting a synoptic surveillance mission over the Gulf of Mexico and dropsondes from that mission will be assimilated into the 0000 UTC numerical models runs. Key Messages: 1. Life-threatening storm surge is likely along portions of the coasts of the Florida Panhandle, Big Bend, and Nature Coast, and a storm surge warning is in effect for these areas. Residents in these areas should follow all advice given by their local officials. 2. A hurricane warning has been issued for portions of the Florida Gulf Coast, and everyone in these areas should prepare for life-threatening winds associated with the core of Michael. Damaging winds will also extend inland across portions of the Florida Panhandle, southern Georgia, and southeast Alabama as Michael moves inland. 3. Heavy rainfall from Michael could produce life-threatening flash flooding from the Florida Panhandle and Big Bend region into portions of Georgia and South Carolina. 4. Hurricane conditions will continue in portions of western Cuba through this evening, where a hurricane warning is in effect. 5. Michael is expected to produce heavy rainfall and flash flooding over portions of western Cuba and the northeastern Yucatan Peninsula of Mexico during the next couple of days. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 22.2N 85.2W 70 KT 80 MPH 12H 09/0600Z 23.7N 85.7W 85 KT 100 MPH 24H 09/1800Z 25.7N 86.4W 95 KT 110 MPH 36H 10/0600Z 27.9N 86.6W 105 KT 120 MPH 48H 10/1800Z 30.2N 85.8W 100 KT 115 MPH...NEAR THE COAST 72H 11/1800Z 34.5N 80.5W 45 KT 50 MPH...INLAND 96H 12/1800Z 39.8N 68.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 13/1800Z 46.2N 50.0W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Hurricane Sergio Forecast Discussion Number 38

2018-10-08 22:40:19| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Mon Oct 08 2018 000 WTPZ41 KNHC 082040 TCDEP1 Hurricane Sergio Discussion Number 38 NWS National Hurricane Center Miami FL EP212018 200 PM PDT Mon Oct 08 2018 Sergio still consists almost entirely of a solid ring of deep convection surrounding a very large eye. A pair of timely ASCAT passes from around 1800 UTC show that the hurricane wind field remains very symmetric with a large RMW. Although we wouldn't expect that instrument to capture the true magnitude of the hurricane's maximum winds, the data does suggest that the winds have decreased at least a little since this morning. UW-CIMSS SATCON values have also decreased, so the initial intensity is lowered slightly to 75 kt. The hurricane is moving very slowly northward, around 3 kt. There has been no change to the reasoning behind the track forecast and Sergio should still accelerate northeastward in a day or so, approaching the Baja California peninsula by the end of the week. Nearly all of the models have shifted a little toward the south beyond 24 h, and the NHC track forecast has been adjusted in that direction as well, but now lies just north of the multi-model consensus. In the short-term, Sergio is still forecast to gradually weaken while it moves very little and continues to upwell cold waters. Beyond 24 h, the hurricane should reach additional cooler waters to the north, which should cause additional gradual weakening. In general, the intensity guidance is forecasting Sergio to maintain its intensity a little longer than previously forecast, so the NHC intensity forecast has been adjusted a little higher at 48 h and 72 h. It's worth noting that the hurricane would likely maintain its intensity longer if it moves a little farther south over warmer waters, and any further adjustments southward to the track forecast could have implications on the intensity forecast. By Friday afternoon, the cyclone should have reached the Baja California peninsula and more rapid weakening should follow. Although the low-level center of Sergio will likely quickly dissipate after reaching mainland Mexico, its mid-level remnants and moisture will continue northeastward, potentially causing heavy rainfall across parts of the southwestern United States. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 15.7N 128.5W 75 KT 85 MPH 12H 09/0600Z 16.2N 128.1W 70 KT 80 MPH 24H 09/1800Z 16.9N 127.0W 70 KT 80 MPH 36H 10/0600Z 17.7N 125.4W 65 KT 75 MPH 48H 10/1800Z 18.9N 123.2W 60 KT 70 MPH 72H 11/1800Z 22.9N 118.0W 55 KT 65 MPH 96H 12/1800Z 28.0N 111.5W 40 KT 45 MPH 120H 13/1800Z 33.5N 102.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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Hurricane Sergio Forecast Discussion Number 37

2018-10-08 16:48:16| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Mon Oct 08 2018 000 WTPZ41 KNHC 081448 TCDEP1 Hurricane Sergio Discussion Number 37 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Mon Oct 08 2018 Sergio's structure has remained nearly steady-state for the past 24 hours. A solid ring of deep convection surrounds Sergio's giant eye, and there is little evidence of any convective bands. Despite upwelling that is presumably occuring beneath the slow moving hurricane, cloud tops have actually cooled over the past few hours, and satellite intensity estimates from TAFB and SAB have not changed. The initial intensity has therefore been held at 80 kt, which also agrees with a 1045 UTC UW-CIMSS SATCON estimate. As long as Sergio can maintain its annular structure in an environment of negligible shear, only very gradual weakening is expected, despite presumably cooling waters beneath the cyclone associated with its slow movement. The ECMWF and GFS forecast that the shear will begin to increase in about 24 to 36 hours, and the cyclone will also be reaching much cooler waters shortly after that time. A faster rate of weakening is therefore anticipated beyond 48 h, in line with the latest intensity consensus, and Sergio is forecast to be a tropical storm when it approaches northwestern Mexico in a few days. The cyclone should weaken quickly after landfall, and will likely dissipate over the high terrain of mainland Mexico, though a 5 day remnant low point is still shown for continuity purposes. Sergio is moving very little right now, and the slow motion will likely continue during the day today. By tonight, a large trough centered over the southwestern United States will cause the hurricane to accelerate northeastward. The track guidance is in good agreement on the track of Sergio, although there is still some uncertainty associated with the timing for when Sergio will reach the west coast of the Baja California peninsula. Only minor changes were made to the official track forecast, which lies near the middle of the guidance envelope and very close to TVCN. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 15.3N 128.6W 80 KT 90 MPH 12H 09/0000Z 15.9N 128.4W 75 KT 85 MPH 24H 09/1200Z 16.6N 127.6W 70 KT 80 MPH 36H 10/0000Z 17.4N 126.1W 65 KT 75 MPH 48H 10/1200Z 18.6N 124.0W 65 KT 75 MPH 72H 11/1200Z 22.3N 119.0W 55 KT 65 MPH 96H 12/1200Z 27.5N 113.0W 40 KT 45 MPH...INLAND 120H 13/1200Z 33.0N 105.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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