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Tropical Storm Nadine Forecast Discussion Number 6

2018-10-10 16:49:36| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Oct 10 2018 000 WTNT45 KNHC 101449 TCDAT5 Tropical Storm Nadine Discussion Number 6 NWS National Hurricane Center Miami FL AL152018 1100 AM AST Wed Oct 10 2018 Several microwave overpasses after 0600 UTC indicated that Nadine very quickly developed a well-defined mid-level eye overnight. This signature is typically associated with strengthening tropical cyclones. Although more recent visible imagery indicates that strong shear has since caused the cyclone to become tilted with height, a pair of ASCAT passes around 1200 UTC indicated maximum winds of 45-50 kt. Given the small size of the tropical storm, the ASCAT likely under-sampled the true maximum, so the initial intensity has been raised to 55 kt. Due to limitations in our ability to observe the intensity of small tropical storms far from land, it should be noted that this estimate is fairly uncertain. Since the tropical storm appears to have become more tilted since last night, further strengthening is not likely. Shear analysis from UW-CIMSS shows that Nadine is moving into a region of 20-30 kt of westerly shear, and SHIPS diagnostics indicate that the shear could increase to near 40 kt in another couple of days. All of the intensity guidance indicates that Nadine will weaken quickly by tomorrow, and it could become a depression by 72 h. Dissipation will likely follow shortly after, as shown by nearly all of the global and regional models. The aforementioned ASCAT passes were very helpful in locating the center of Nadine at 1200 UTC, and the tropical storm is moving northwestward, or 325/6 kt. A northwestward to north-northwestward motion at a similar forward speed is anticipated for the next day or two. By Friday, a turn toward the west will likely begin as the low-level circulation of Nadine becomes separated from its convection and turns westward in the low-level easterlies. Nadine is essentially on the track of the previous NHC forecast, and no significant changes to the track forecast were required. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 12.6N 31.6W 55 KT 65 MPH 12H 11/0000Z 13.5N 32.1W 55 KT 65 MPH 24H 11/1200Z 14.6N 32.9W 50 KT 60 MPH 36H 12/0000Z 15.7N 33.9W 45 KT 50 MPH 48H 12/1200Z 16.5N 35.2W 35 KT 40 MPH 72H 13/1200Z 17.5N 39.1W 30 KT 35 MPH 96H 14/1200Z...DISSIPATED $$ Forecaster Zelinsky

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Hurricane Leslie Forecast Discussion Number 57

2018-10-10 16:47:04| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Oct 10 2018 000 WTNT43 KNHC 101446 TCDAT3 Hurricane Leslie Discussion Number 57 NWS National Hurricane Center Miami FL AL132018 1100 AM AST Wed Oct 10 2018 Leslie has continued to get better organized this morning, and several recent microwave overpasses indicate that the hurricane is maintaining a well-defined mid-level eye. However, objective and subjective intensity estimates have not increased, so the intensity has been held at 65 kt. All of the intensity guidance forecasts that Leslie will resume intensifying later today. Given that the hurricane is located in a low shear environment and crossing over the warmest waters it has encountered in days, this seems very likely. No change was made to the intensity forecast through 48 h. Beyond that time, the intensity forecast is still tied to the track forecast, and the farther south and west Leslie remains, the stronger it will likely be. Extratropical transition also can not be ruled out, which would likely result in a higher intensity by day 5 that indicated by the NHC forecast. The official intensity forecast is still close to the model consensus through day 5, but a large range of possibilities exists by that time, from Leslie becoming a weak post-tropical low, to maintaining near hurricane strength. The spread in the track guidance is still very large and confidence in the track forecast is low. The most recent ECMWF ensemble has a 5-day spread of over 1500 n mi, while the 5-day GFS ensemble spread is over 1300 n mi. Leslie is forecast to slow down today and turn toward the east-northeast. A faster motion in that direction is anticipated by tomorrow as a mid-latitude trough approaches from the northwest. Leslie will then either undergo extratropical transition and lift northward, continue westward and become a remnant low, or separate from the trough and turn back west. The NHC forecast is near the track consensus at all times and no large changes to the forecast were made since the future track of the cyclone has not become more clear. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 27.8N 42.3W 65 KT 75 MPH 12H 11/0000Z 27.8N 41.6W 70 KT 80 MPH 24H 11/1200Z 28.4N 39.7W 75 KT 85 MPH 36H 12/0000Z 29.6N 36.2W 80 KT 90 MPH 48H 12/1200Z 30.7N 31.8W 75 KT 85 MPH 72H 13/1200Z 31.5N 23.0W 60 KT 70 MPH 96H 14/1200Z 29.5N 22.0W 40 KT 45 MPH 120H 15/1200Z 27.0N 26.0W 35 KT 40 MPH $$ Forecaster Zelinsky

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Tropical Storm Sergio Forecast Discussion Number 45

2018-10-10 16:45:34| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Wed Oct 10 2018 000 WTPZ41 KNHC 101445 TCDEP1 Tropical Storm Sergio Discussion Number 45 NWS National Hurricane Center Miami FL EP212018 800 AM PDT Wed Oct 10 2018 The cloud pattern associated with Sergio has not changed very much, and it consists of a cyclonically curved convective band surrounding a large and ragged eye feature. Since the convection is weaker, the Dvorak estimates suggest that winds are gradually decreasing, and the initial intensity has been lowered to 55 kt. Some fluctuations in intensity are likely during the next 12 to 24 hours while the cyclone is still moving over relatively warm waters and is embedded in a low shear environment. Both of these factors will become unfavorable soon, and consequently, the NHC forecast calls for weakening. Sergio, however, is expected to still be a tropical storm by the time it approaches the Baja California peninsula. After that time, Sergio will move over mainland Mexico and weaken much faster. Sergio is moving toward the northeast or 055 degrees at 11 kt. The cyclone is embedded within the southwesterly winds associated with a large mid-latitude trough, and this flow pattern will continue to steer Sergio toward the northeast with an increase in forward speed. The forecast track brings the center of a weakened Sergio over the central portion of the Baja California peninsula in about 2 days, but winds along the coast are anticipated to increase earlier. Track models are in very good agreement, and consequently the guidance envelope is quite tight. The NHC forecast is not different from the previous one and is in the middle of the guidance envelope. The primary threat associated with Sergio and its remnants continues to be life-threatening flash flooding and mudslides within mountainous terrain in the Mexico state of Sonora, the U.S. Southern Plains, and the Ozarks 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 10/1500Z 18.4N 123.5W 55 KT 65 MPH 12H 11/0000Z 19.7N 121.6W 50 KT 60 MPH 24H 11/1200Z 22.0N 119.0W 50 KT 60 MPH 36H 12/0000Z 24.5N 116.2W 45 KT 50 MPH 48H 12/1200Z 27.0N 113.0W 40 KT 45 MPH 72H 13/1200Z 31.5N 104.5W 25 KT 30 MPH...POST-TROP/INLAND 96H 14/1200Z...DISSIPATED $$ Forecaster Avila

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Hurricane Michael Forecast Discussion Number 15

2018-10-10 10:54:32| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Wed Oct 10 2018 000 WTNT44 KNHC 100854 TCDAT4 Hurricane Michael Discussion Number 15 NWS National Hurricane Center Miami FL AL142018 400 AM CDT Wed Oct 10 2018 Reports from an Air Force Reserve Hurricane Hunter aircraft indicate that Michael has continued to strengthen during the past several hours. The maximum flight-level winds at 700 mb have been 136 kt, and the maximum surface wind estimates from the Stepped Frequency Microwave Radiometer are in the 120-125 kt range. In addition, the central pressure has fallen to near 943 mb. Based on on the aircraft data, the initial intensity is increased to 120 kt. This is a little below the satellite intensity estimates from TAFB, SAB, and the CIMSS satellite consensus. The cirrus outflow associated with Michael has improved over the past several hours, with the outflow flowing into an upper-level low to the southeast and along the east side of a large mid-latitude trough to the west. The initial motion is 360/11. Michael is embedded in the flow between a large mid- to upper-level ridge over the western Atlantic and the northeastern United States and the aforementioned trough across the central United States. These features should cause the hurricane to turn north-northeastward during the next 12 h or so, followed by a turn toward the northeast and a significant increase in forward speed. Near the end of the forecast period, Michael or its remnants should turn more eastward. The forecast track calls for the eye to make landfall in the Florida Panhandle at about the 12 h point, followed by a northeastward motion across the southeastern United States between 12-48 h. The forecast guidance remains tightly clustered, and the new forecast track is very close to the previous track and the various consensus models through 72 h. Additional strengthening is expected before landfall as Michael remains over warm water and in an environment of light to moderate vertical shear. After landfall, Michael is expected to steadily weaken as it crosses the southeastern United States. Extratropical transition is expected to begin while Michael is over land, and this should be complete just after the 48 h point. The cyclone should re-intensify due to baroclinic forcing as it moves rapidly northeastward over the north Atlantic. The new intensity forecast has been nudged upward at the landfall time based on current trends. Otherwise, it is an update of the previous forecast. Tropical storm conditions are expected to reach the hurricane warning area during the next few hours, 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 Tyndall Air Force Base and Keaton Beach, where 9 to 13 feet of inundation is possible. 2. Michael is likely to produce potentially catastrophic wind damage where the core of the hurricane moves onshore in the Florida Panhandle, and everyone in the hurricane warning area should prepare for life-threatening hurricane winds. Dangerous 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 10/0900Z 28.3N 86.5W 120 KT 140 MPH 12H 10/1800Z 29.9N 85.7W 125 KT 145 MPH 24H 11/0600Z 32.1N 83.8W 65 KT 75 MPH...INLAND 36H 11/1800Z 34.4N 80.5W 40 KT 45 MPH...INLAND 48H 12/0600Z 36.8N 75.6W 40 KT 45 MPH...OVER WATER 72H 13/0600Z 43.5N 59.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 14/0600Z 49.5N 36.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 15/0600Z 52.0N 17.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Tropical Storm Sergio Forecast Discussion Number 44

2018-10-10 10:43:03| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Wed Oct 10 2018 000 WTPZ41 KNHC 100842 TCDEP1 Tropical Storm Sergio Discussion Number 44 NWS National Hurricane Center Miami FL EP212018 200 AM PDT Wed Oct 10 2018 This morning's conventional satellite presentation reveals little change in Sergio's cloud pattern. The majority of the deep convection resides in the north portion of the circulation with some new bursts developing in the south semicircle. Consequently, the initial intensity will be kept again at 60 kt, and is supported by the TAFB and SAB Dvorak intensity estimates. Gradual spin down of the cyclone is still expected to commence soon as Sergio begins its trek over decreasing sea surface temperatures and into a region of increasing southwesterly vertical shear and a drier mid-level troposphere. Over the weekend, after quickly moving over the central Baja California peninsula, Sergio should weaken further over the state of Sonora in northwestern Mexico, degenerate into a remnant low early Sunday, and is forecast to dissipate over the Southern Plains of the United States, although this dissipation could occur sooner, as indicated in the European global models. The initial motion is estimated to be east-northeastward, or 065/10 kt, within the mid-tropospheric southwesterly flow produced by a mid-latitude trough extending southwestward over the eastern Pacific from the southwestern United States. Sergio should continue to accelerate toward the east-northeast or northeast over the next few days, and approach Baja California Sur on early Friday. The NHC forecast is basically an update of the previous advisory and is close to the various multi-model consensus aids. The primary threat associated with Sergio and its remnants will likely be life-threatening flash flooding and mudslides within mountainous terrain in the Mexico state of Sonora, the U.S. Southern Plains and the Ozarks 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 10/0900Z 17.5N 124.9W 60 KT 70 MPH 12H 10/1800Z 18.8N 122.9W 55 KT 65 MPH 24H 11/0600Z 20.6N 120.4W 55 KT 65 MPH 36H 11/1800Z 23.0N 117.7W 50 KT 60 MPH 48H 12/0600Z 25.4N 114.7W 50 KT 60 MPH 72H 13/0600Z 30.3N 107.3W 35 KT 40 MPH...INLAND 96H 14/0600Z 34.5N 97.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 15/0600Z...DISSIPATED $$ Forecaster Roberts

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