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Hurricane Sergio Forecast Discussion Number 41

2018-10-09 16:48:55| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Tue Oct 09 2018 000 WTPZ41 KNHC 091448 TCDEP1 Hurricane Sergio Discussion Number 41 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Tue Oct 09 2018 Sergio appears to have resumed its slow weakening. Cloud tops on the western half of the hurricane have warmed, and Dvorak classifications from TAFB and SAB have decreased. However, recent AMSR-2 and SSMIS images indicate that the hurricane still has a large but well-defined inner-core in the low and mid-levels. The initial intensity is set at 70 kt, based on a blend of Final-T and CI numbers from TAFB and SAB, and the most recent UW-CIMSS SATCON estimate. There has been almost no change to the intensity forecast and only very gradual weakening is forecast during the next 36 to 48 h. Beyond that time, Sergio will pass over colder SSTs, including the still-present cold wake of former Hurricane Rosa, and continued weakening is expected as the cyclone approaches the Baja California peninsula. Sergio is therefore still forecast to be a tropical storm when it reaches the west coast of the Baja California peninsula in a few days. Rapid weakening is likely after Sergio makes its final landfall in northwestern mainland Mexico late this week, and the cyclone will likely dissipate or become a remnant low shortly after moving inland. Virtually no change has been made to the track forecast, which remains near the TVCN and HCCA consensus aids. All of the global and regional models show that Sergio will accelerate generally northeastward for the next 3 days, approaching the Baja California peninsula on Friday. There is still some disagreement among the models regarding the exact speed of Sergio through that time, but there is very little cross-track spread. Confidence in the track forecast is fairly high. Moisture associated with the remnants of Sergio is expected to affect portions of northwestern Mexico, the southwestern United States, and the U.S. southern plains over the weekend and could potentially cause heavy rainfall in this region. For more information about this potential hazard, see products from the Weather Prediction Center and your local NWS forecast office. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 16.6N 127.4W 70 KT 80 MPH 12H 10/0000Z 17.1N 126.3W 65 KT 75 MPH 24H 10/1200Z 18.1N 124.4W 65 KT 75 MPH 36H 11/0000Z 19.7N 122.0W 60 KT 70 MPH 48H 11/1200Z 21.7N 119.3W 60 KT 70 MPH 72H 12/1200Z 26.2N 113.5W 50 KT 60 MPH 96H 13/1200Z 31.0N 106.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 14/1200Z...DISSIPATED $$ Forecaster Zelinsky

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Hurricane Michael Forecast Discussion Number 12

2018-10-09 16:43:56| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Tue Oct 09 2018 000 WTNT44 KNHC 091443 TCDAT4 Hurricane Michael Discussion Number 12 NWS National Hurricane Center Miami FL AL142018 1000 AM CDT Tue Oct 09 2018 Michael has continued to become better organized this morning. The hurricane has become more symmetric with the eye becoming more apparent in infrared and visible satellite imagery. Data from both NOAA and U.S. Air Force Reserve Hurricane Hunter aircraft show that the minimum pressure has dropped to around 965 mb, and a blend of the flight-level and SFMR winds support an initial intensity of 95 kt for this advisory. With two aircraft in the storm, they have been able to sample each of the four quadrants a couple of times this morning, providing better confidence in the analyzed wind field. The planes actually passed through the eye around the same time just before 1200 UTC, and reported that they could see one another. The outflow pattern has become better established over the hurricane, but there is still a little evidence of some westerly shear. The shear should continue to decrease, and further strengthening is expected until landfall on Wednesday. Michael is expected to become a major hurricane later today, and remain a dangerous major hurricane through landfall. Significant weakening should occur as the center moves inland over the southeastern United States, but re-strengthening as an extratropical low is expected when the system moves over the western Atlantic. Michael is moving between north-northwest and north at about 10 kt. The track forecast reasoning is the same as the past several advisories, as Michael should move generally northward through early Wednesday between a ridge over the western Atlantic and a deep-layer trough over the central United States. As the trough moves eastward it will cause Michael to turn northeastward on Wednesday. The hurricane should then continue northeastward and accelerate as it becomes embedded in the mid-latitude westerlies. The track guidance is in very good agreement through the first 36-48 hours, with some differences in forward speed thereafter. The GFS and ECMWF have trended slower after landfall, and the new NHC track has been adjusted accordingly. 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. 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 and South Carolina. 4. Michael is expected to produce heavy rainfall and flash flooding over portions of western Cuba during the next day or so. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 25.0N 86.2W 95 KT 110 MPH 12H 10/0000Z 26.7N 86.5W 105 KT 120 MPH 24H 10/1200Z 28.8N 86.3W 110 KT 125 MPH 36H 11/0000Z 30.8N 85.1W 75 KT 85 MPH...INLAND 48H 11/1200Z 33.0N 82.5W 45 KT 50 MPH...INLAND 72H 12/1200Z 37.5N 74.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 13/1200Z 44.0N 56.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 14/1200Z 50.0N 38.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Storm Leslie Forecast Discussion Number 53

2018-10-09 16:40:24| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Oct 09 2018 000 WTNT43 KNHC 091440 TCDAT3 Tropical Storm Leslie Discussion Number 53 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Tue Oct 09 2018 Recent Dvorak fixes and ASCAT data indicate that Leslie's maximum winds remain around 55 kt. Although the winds have not yet increased, the surface center of the tropical storm has become more embedded within its cold cloud tops and several recent microwave overpasses indicate that the cyclone is beginning to establish an inner-core. Strengthening is therefore still expected, and Leslie is forecast to become a hurricane by tomorrow. The tropical storm is currently moving south-southeastward at around 11 kt, and the models are in good agreement that a south-southeastward to southward motion will continue for the next 24 h or so. Beginning around 36 h, both the track and intensity forecasts become very uncertain. In general, most of the global models and their ensembles indicate that Leslie will begin to accelerate toward the east-northeast or northeast by Thursday as a mid-latitude trough approaches from the northwest, however the timing and extent of the interaction is still highly variable from model to model. Based on the GFS and ECMWF ensembles, a range of possibilities exists, from Leslie essentially merging with this trough and becoming extratropical over the far northeast Atlantic, to Leslie interacting with the trough very little and continuing to meander over the central Atlantic. There has been a significant change in the consensus aids to show a slower track for Leslie based on recent shifts in the deterministic models, but the NHC track forecast has not been changed nearly as much, out of respect for continuity and the high uncertainty in the forecast. The low confidence in the track forecast beyond 36 h affects the intensity forecast as well, since it is unclear what environment the storm will be located within. The intensity forecast is therefore held near the intensity consensus, and still calls for steady strengthening during the next several days, followed by weakening by the end of the forecast period. If Leslie moves as far east as shown in the NHC track forecast, it would likely become a post- tropical low by day 5, as shown explicitly in the forecast. However, until confidence in the track increases, I can't rule out that Leslie could remain a tropical cyclone almost indefinitely if it continues meandering over the northern Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 31.3N 43.5W 55 KT 65 MPH 12H 10/0000Z 29.9N 42.9W 55 KT 65 MPH 24H 10/1200Z 28.5N 42.6W 60 KT 70 MPH 36H 11/0000Z 28.1N 41.7W 65 KT 75 MPH 48H 11/1200Z 28.9N 39.5W 70 KT 80 MPH 72H 12/1200Z 32.0N 31.5W 75 KT 85 MPH 96H 13/1200Z 33.5N 22.0W 65 KT 75 MPH 120H 14/1200Z 33.5N 18.0W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Zelinsky

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Tropical Storm Nadine Forecast Discussion Number 2

2018-10-09 16:35:24| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Oct 09 2018 000 WTNT45 KNHC 091435 TCDAT5 Tropical Storm Nadine Discussion Number 2 NWS National Hurricane Center Miami FL AL152018 1100 AM AST Tue Oct 09 2018 The cloud pattern of the cyclone features a curved band that wraps around the eastern and southern parts of the circulation. Dvorak estimates from TAFB and SAB are both T2.5/35 kt, and that is used for the initial intensity, making the system a tropical storm. The environment appears conducive for some additional strengthening during the next 24 hours or so, with SSTs above 28C and generally light to moderate westerly shear. After that time, the shear increases to 25-30 kt and SSTs along the forecast track fall below 27C by 72 hours. These factors should result in weakening, and all of the global models show the cyclone dissipating in 4 to 5 days. The NHC forecast follows these trends and is close to the various consensus aids through the forecast period. Based on geostationary imagery and a 0815Z SSMIS pass, the initial motion estimate is a somewhat uncertain 285/08, with Nadine currently situated south of a narrow mid-level ridge. The ridge will weaken as a mid/upper-level trough that Leslie is embedded in digs southward along 40W longitude. This pattern will cause Nadine to turn more northwestward by 24 hours. By 96 hours, a weakening Nadine should bend back to the west as a shallow system. The new NHC track forecast is a bit to the right of the previous one due to the new initial position, and lies near HCCA through 48 hours and closer to the TVCA multi-model consensus after that time. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 10.5N 30.0W 35 KT 40 MPH 12H 10/0000Z 11.1N 31.0W 40 KT 45 MPH 24H 10/1200Z 11.9N 32.1W 45 KT 50 MPH 36H 11/0000Z 13.0N 33.0W 45 KT 50 MPH 48H 11/1200Z 14.3N 34.1W 40 KT 45 MPH 72H 12/1200Z 16.7N 36.6W 30 KT 35 MPH 96H 13/1200Z 18.0N 40.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 14/1200Z...DISSIPATED $$ Forecaster Brennan

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Tropical Depression Fifteen Forecast Discussion Number 1

2018-10-09 11:52:24| National Hurricane Center (Atlantic)

Issued at 600 AM AST Tue Oct 09 2018 000 WTNT45 KNHC 090952 TCDAT5 Tropical Depression Fifteen Special Discussion Number 1 NWS National Hurricane Center Miami FL AL152018 600 AM AST Tue Oct 09 2018 Geostationary satellite and recent microwave data indicate that the low pressure system over the eastern Atlantic Ocean has developed sufficently organized deep convection and a well-defined center of circulation to be considered a tropical depression, the fifteenth one of the 2018 Atlantic hurricane season. The initial intensity is set at 30 kt, in agreement with Dvorak 2.0/30 kt classifications from both TAFB and SAB. The depression is expected to strengthen a little during the next 36 to 48 hours while it remains in favorable oceanic and atmospheric conditions. Thereafter, a significant increase in west-southwesterly shear, drier air, and slightly cooler SSTs should cause weakening. The global models all show the depression opening up into a trough by day 5, and the official forecast predicts dissipation accordingly. The initial motion is uncertain since the system just formed a well-defined center, but my best guess is 285/10 kt. The depression is expected to turn northwestward tonight and continue in that general direction on Wednesday and Thursday as it moves toward a broad trough over the central Atlantic, the same one that Leslie is embedded in. After that time, when the system weakens and becomes shallow, a turn back to the left is forecast. The models are in fair agreement, and the NHC track forecast lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 09/1000Z 10.3N 29.7W 30 KT 35 MPH 12H 09/1800Z 10.6N 30.8W 30 KT 35 MPH 24H 10/0600Z 11.3N 32.1W 35 KT 40 MPH 36H 10/1800Z 12.4N 33.0W 40 KT 45 MPH 48H 11/0600Z 13.6N 34.0W 40 KT 45 MPH 72H 12/0600Z 16.1N 36.0W 35 KT 40 MPH 96H 13/0600Z 17.5N 39.5W 30 KT 35 MPH 120H 14/0600Z...DISSIPATED $$ Forecaster Cangialosi

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