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Tropical Storm Nadine Forecast Discussion Number 5

2018-10-10 10:35:35| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Oct 10 2018 000 WTNT45 KNHC 100835 TCDAT5 Tropical Storm Nadine Discussion Number 5 NWS National Hurricane Center Miami FL AL152018 500 AM AST Wed Oct 10 2018 Nadine continues to gradually strengthen. Microwave images indicate that the storm is beginning to develop an inner core with a concentrated area of deep convection noted in infrared satellite imagery. The initial intensity is raised to 45 kt, in agreement with 3.0/45 kt Dvorak classifications from TAFB and SAB. Nadine has about another day to strengthen while it remains in favorable atmospheric conditions of low wind shear and high moisture, and over warm waters. The NHC intensity forecast follows the HCCA and IVCN guidance and brings Nadine to 55 kt during that time period. Thereafter, the global models all show a sharp increase in southwesterly shear and that should end the opportunity for strengthening and cause weakening. The combination of strong shear, drier air, and slightly cooler SSTs should cause the cyclone to open into a trough in 3 to 4 days, or perhaps even sooner. The compact storm is moving north-northwestward at 6 kt, and the center is a little to the right of the previous forecast track. A continued northwest to north-northwest motion is expected during the next couple of days while Nadine moves toward a trough over the east-central Atlantic, the same trough that Leslie is embedded in. After that time, the weak and shallow system should turn to the left until dissipation. The NHC track forecast has been adjusted a little to the right of the previous one due to the more northward initial motion and position. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 12.1N 31.1W 45 KT 50 MPH 12H 10/1800Z 12.8N 31.7W 50 KT 60 MPH 24H 11/0600Z 13.9N 32.5W 55 KT 65 MPH 36H 11/1800Z 15.1N 33.4W 45 KT 50 MPH 48H 12/0600Z 16.0N 34.7W 35 KT 40 MPH 72H 13/0600Z 17.3N 38.3W 25 KT 30 MPH 96H 14/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane Leslie Forecast Discussion Number 56

2018-10-10 10:34:34| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Oct 10 2018 000 WTNT43 KNHC 100834 TCDAT3 Hurricane Leslie Discussion Number 56 NWS National Hurricane Center Miami FL AL132018 500 AM AST Wed Oct 10 2018 Geostationary satellite and microwave images indicate that Leslie has a large and ragged banded eye feature with deep convection most organized over the northern semicircle. Since the Dvorak classifications from TAFB and SAB are unchanged at 4.0/65 kt, the initial wind speed is held at that value. Leslie has another day or two to strengthen while it remains in low wind shear conditions and over marginally warm waters. After that time, an increase in shear and lower SSTs should cause Leslie to weaken. It is possible that Leslie could become a post-tropical cyclone by day 5, but confidence is not high on that occurring. The NHC intensity forecast is largely an update of the previous one and it lies at the high end of the model guidance. Leslie is now moving southward at 9 kt in the flow on the southwest side of a broad mid- to upper-level trough. A slower south- southeastward motion is expected during the day today as the trough pulls away. A turn to the east-northeast is expected tonight as another trough approaches Leslie from the northwest, and that motion with an increase in forward speed is expected through early this weekend. After that time, the models are coming into better agreement in showing Leslie being left behind and moving southwestward on Sunday and Monday as a ridge builds to its northwest. The NHC track forecast is adjusted southward at days 3 to 5 to be closer to the latest consensus aids. Although the deterministic models are in better agreement this cycle, there is still a lot of spread in the GFS and ECMWF ensemble members and confidence in the track forecast remains fairly low. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 28.6N 42.6W 65 KT 75 MPH 12H 10/1800Z 28.0N 42.3W 70 KT 80 MPH 24H 11/0600Z 28.1N 40.9W 75 KT 85 MPH 36H 11/1800Z 29.1N 38.3W 80 KT 90 MPH 48H 12/0600Z 30.5N 34.2W 75 KT 85 MPH 72H 13/0600Z 31.5N 25.0W 70 KT 80 MPH 96H 14/0600Z 30.5N 21.5W 50 KT 60 MPH 120H 15/0600Z 28.5N 23.5W 40 KT 45 MPH $$ Forecaster Cangialosi

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Hurricane Michael Forecast Discussion Number 14

2018-10-10 04:52:57| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Tue Oct 09 2018 000 WTNT44 KNHC 100252 TCDAT4 Hurricane Michael Discussion Number 14 NWS National Hurricane Center Miami FL AL142018 1000 PM CDT Tue Oct 09 2018 Data from Air Force Reserve and NOAA Hurricane Hunter aircraft this afternoon and evening indicate that Michael has been undergoing a rapid deepening phase with the pressure having dropped to 947 mb, a decrease of 20 mb between 1800Z and 0200Z with most of those pressures falls occurring during the past few hours. Michael's eye has become more distinct in GOES-16 high-resolution infrared satellite imagery, with a solid ring of cloud top temperatures colder than -75 deg C surrounding the warming eye. Some cloud tops in the eyewall have been as cold as -88C, which is very impressive for a Gulf system. The peak 8000-ft flight-level winds measured by the NOAA aircraft thus far has been 130 kt and the strongest SFMR surface wind speed observed has been 110 kt in the same location as the peak flight-level winds. Based on these wind data, along with a central pressure of 947 mb, Michael's intensity has been increased to 110 kt. Satellite intensity estimates from TAFB and SAB, along with objective estimates from UW-CIMSS ADT and NHC, support an intensity of 115-127 kt. However, those also estimates also would support a central pressure of about 935 mb, which the aircraft has not measured thus far. The initial motion estimate is due north, or 360/10 kt. Michael is essentially on the previous advisory track, and there is no significant change to the previous track forecast discussion. The models have settled in a stable forecast pattern, which calls for Michael to remain embedded within deep southerly flow for the next 24 hours between a substantial ridge to the east and a highly amplified mid-latitude trough moving eastward across the western and central U.S. and northern Mexico. As a result, the dangerous hurricane is expected to move northward to north-northeastward and make landfall along the coast of the central panhandle of Florida by late Wednesday afternoon. After landfall, increasing southwesterly flow ahead of the approaching deep-layer trough is expected to accelerate Michael toward the northeast through 48 h, with the cyclone moving across the southeastern U.S. late Wednesday and Thursday, and emerging over the western Atlantic by early Friday. A continued northeastward motion at forward speeds of 30-40 kt is forecast at 72-120 h when Michael is expected to be an extratropical cyclone. The new NHC forecast track is essentially just an update of the previous advisory track, and lies close to the tightly packed consensus models TVCN, TVCX, TCON, and NOAA-HCCA. Similar to the previous advisory, the environment ahead of Michael is expected to remain conducive for additional strengthening until landfall occurs due to SSTs of at least 85 deg F beneath the hurricane, combined with decreasing vertical wind shear along with the shear vector shifting from current west-northwesterly to a less hostile southwesterly component, which will be more along Michael's forecast track. As a result, Michael is now explicitly forecast to become a category 4 hurricane before landfall occurs. After landfall, significant weakening is expected while Michael moves over the southeastern United States, but the cyclone is forecast to re-strengthen over the western Atlantic due to baroclinic forcing after it merges with a front and becomes extratropical on Friday. The new intensity forecast closely follows a blend of the IVCN, HCCA, and FSSE consensus models throughout the 120-h period. Tropical storm conditions are expected to reach the hurricane warning area by Wednesday morning, so all preparations should be rushed to completion. Key Messages: 1. Life-threatening storm surge is likely along portions of the coasts of the Florida Panhandle, Big Bend, and Nature Coast, where a storm surge warning is in effect. The worst storm surge is expected between Mexico Beach and Keaton Beach, where 9 to 13 feet of inundation is possible. Water levels will rise well in advance of the center of Michael, and residents within the storm surge warning area should finish preparations to protect life and property today. 2. Everyone in the hurricane warning area along the Florida Gulf Coast should prepare for life-threatening major hurricane winds associated with the core of Michael. Hurricane force winds will also extend well 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, the Carolinas, and southeast Virginia. 4. Tropical storm conditions will likely affect portions of the southeast U.S. coast from northeast Florida through North Carolina, and tropical storm watches and warnings are in effect for these areas. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 27.1N 86.5W 110 KT 125 MPH 12H 10/1200Z 28.7N 86.2W 115 KT 130 MPH 24H 11/0000Z 30.8N 84.9W 70 KT 80 MPH...INLAND 36H 11/1200Z 33.0N 82.4W 40 KT 45 MPH...INLAND 48H 12/0000Z 35.2N 78.6W 40 KT 45 MPH...INLAND 72H 13/0000Z 40.8N 65.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 14/0000Z 47.2N 44.8W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 15/0000Z 51.2N 24.9W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Hurricane Leslie Forecast Discussion Number 55

2018-10-10 04:43:31| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Oct 09 2018 000 WTNT43 KNHC 100243 TCDAT3 Hurricane Leslie Discussion Number 55 NWS National Hurricane Center Miami FL AL132018 1100 PM AST Tue Oct 09 2018 Satellite and microwave data indicate that Leslie has become a hurricane again, almost exactly a week after it did the first time. A WindSat pass from earlier today showed the development of an eye feature, and with the Dvorak estimates from TAFB and SAB at hurricane strength, the initial wind speed is set to 65 kt. The latest GOES-16 proxy visible imagery suggests that a ragged eye has formed, although the eyewall is open on the southwestern side. Leslie is atypically intensifying while moving south-southeastward at 8 kt. The hurricane should continue to lose latitude for a day or so then get accelerated east-northeastward by a mid-latitude trough until Friday. After that time, there is a ginormous spread in the model ensembles with Leslie's final destination ranging from Ireland all the way to missing the trough and turning around to the southwest due to a building eastern Atlantic subtropical ridge. Compared to 12 hours ago, more of the ensemble members are showing Leslie getting left behind, which is also reflected in the latest deterministic runs as well. Something tells me that Leslie has at least one more trick up its sleeve, so the official forecast shows this trend, but is very low confidence. With fairly low shear and marginally warm waters for the next day or two, there is no reason to expect that Leslie won't continue to intensify. Model guidance is higher than the last cycle, with the normally conservative ECMWF and GFS models even suggesting that Leslie becomes a category 2 hurricane in a couple of days. Most of the rest of the guidance is lower than those models, but the intensity forecast is shaded in the direction of the ECMWF/GFS, and is higher than the last NHC prediction. After that time, an increase in shear and lower SSTs should cause Leslie to weaken. It is even possible it will become a post-tropical cyclone by day 5, but I'm not going to show that at this time since I was too premature last night in this transition. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 29.5N 42.6W 65 KT 75 MPH 12H 10/1200Z 28.4N 42.3W 70 KT 80 MPH 24H 11/0000Z 28.0N 41.6W 75 KT 85 MPH 36H 11/1200Z 28.6N 39.8W 80 KT 90 MPH 48H 12/0000Z 29.9N 36.4W 80 KT 90 MPH 72H 13/0000Z 32.2N 27.0W 75 KT 85 MPH 96H 14/0000Z 32.0N 21.0W 55 KT 65 MPH 120H 15/0000Z 30.0N 22.0W 40 KT 45 MPH $$ Forecaster Blake

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Tropical Storm Nadine Forecast Discussion Number 4

2018-10-10 04:39:04| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Oct 09 2018 000 WTNT45 KNHC 100238 TCDAT5 Tropical Storm Nadine Discussion Number 4 NWS National Hurricane Center Miami FL AL152018 1100 PM AST Tue Oct 09 2018 Deep convection has been increasing in the eastern semicircle of Nadine, with the center close to the western edge of large convective band. Overall, the satellite presentation has improved in the past several hours, although the outflow is limited west of the center. While subjective estimates are unchanged from the last advisory, microwave-based estimates suggest Nadine is somewhat stronger, so the initial wind speed is set to 40 kt. Light or moderate shear is anticipated during the next day or so, along with sufficiently warm waters, which should promote strengthening. However, Nadine should encounter a large upper trough after that time, which will likely cause weakening to begin on Thursday. Later on, cooler SSTs and strong shear are expected to cause Nadine to degenerate into a trough of low pressure by the weekend. The most significant change is that the model guidance is notably higher than the last cycle, with a few models even making Nadine a hurricane eventually. That seems unlikely given the strength of the forecast shear, but the forecast is nudged higher than the previous one and the model consensus. Nadine continues to turn rightward and is now moving northwestward at about 7 kt. This general course is forecast for the next couple of days due to steering from a mid-level ridge near the Cabo Verde Islands. After that time, a west-northwestward or westward turn is expected as Nadine becomes a shallow system and dissipates. The model spread is still fairly wide, with the stronger guidance generally on the eastern side of the model envelope, and the weaker guidance on the western side. There is definitely a slight trend to the northeast with the latest model guidance, and since we are expecting a stronger system, the official forecast is adjusted in that direction, but not nearly as far to the right as most of the GFS-based guidance. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 11.6N 31.0W 40 KT 45 MPH 12H 10/1200Z 12.3N 31.7W 45 KT 50 MPH 24H 11/0000Z 13.4N 32.7W 50 KT 60 MPH 36H 11/1200Z 14.8N 33.7W 45 KT 50 MPH 48H 12/0000Z 16.0N 35.0W 35 KT 40 MPH 72H 13/0000Z 17.5N 38.0W 25 KT 30 MPH 96H 14/0000Z...DISSIPATED $$ Forecaster Blake

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