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Hurricane Leslie Forecast Discussion Number 62

2018-10-11 22:48:43| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Oct 11 2018 000 WTNT43 KNHC 112048 TCDAT3 Hurricane Leslie Discussion Number 62 NWS National Hurricane Center Miami FL AL132018 500 PM AST Thu Oct 11 2018 Leslie's inner-core structure has improved a little during the day today. A ragged banding eye was present in visible imagery until sunset, though this feature is not apparent in IR imagery. Recent satellite intensity estimates range from 65 kt to 90 kt, so Leslie's intensity has been raised to 75 kt as a compromise of all available estimates. Leslie continues to accelerate east-northeastward with an initial motion estimate of 065/18 kt. Confidence remains high that Leslie will continue gaining speed on that heading for the next 24 h or so. Beyond that time, the ensemble spread is still very high, though the 12Z deterministic global models are generally in agreement that Leslie will separate from a mid-level trough, slow down, and turn southward over the weekend. While the exact timing of this turn is still highly uncertain, the multi-model consensus brings Leslie near Madeira Island on Saturday as a tropical storm. The new official forecast shows a very similar track, and the government of Portugal has issued a Tropical Storm Watch for that island. While the exact path of Leslie is still uncertain, the cyclone is still expected to produce tropical storm conditions over a wide area through Saturday, and interests on Madeira should not focus on the exact track of Leslie. No large changes in intensity are anticipated during the next 24 h, though some fluctuations are possible, up or down. By 36 h, Leslie will reach much cooler waters and encounter an increase in wind shear which should lead to steady weakening. The intensity guidance is in surprisingly good agreement given the continued large track spread, and the NHC intensity forecast is near the middle of the guidance envelope from 36 h onward. By 96 h, odds are increasing that Leslie could lose all of its convection and become post-tropical, though this possibility still depends heavily on Leslie following a track similar to the NHC official forecast. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 29.9N 36.5W 75 KT 85 MPH 12H 12/0600Z 31.0N 33.0W 75 KT 85 MPH 24H 12/1800Z 32.5N 27.4W 75 KT 85 MPH 36H 13/0600Z 33.3N 21.6W 65 KT 75 MPH 48H 13/1800Z 33.1N 17.4W 55 KT 65 MPH 72H 14/1800Z 30.9N 16.0W 40 KT 45 MPH 96H 15/1800Z 29.0N 18.5W 30 KT 35 MPH...POST-TROPICAL 120H 16/1800Z 28.0N 24.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky

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Tropical Storm Nadine Forecast Discussion Number 11

2018-10-11 22:39:13| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Oct 11 2018 000 WTNT45 KNHC 112039 TCDAT5 Tropical Storm Nadine Discussion Number 11 NWS National Hurricane Center Miami FL AL152018 500 PM AST Thu Oct 11 2018 Nadine continues to be strongly sheared. A brief burst of deep convection occurred near the center of the cyclone a few hours ago, but the center has since become exposed once again. The initial intensity has been decreased to 45 kt based primary on the latest TAFB and SAB Dvorak fixes. Additional weakening is likely over the next day or so while Nadine remains strongly sheared. The regional and global models now show Nadine degenerating into a trough of low pressure within 48 h, and this is reflected in the new NHC forecast. The tropical storm is moving west-northwestward with an initial speed of 7 kt. The models are in good agreement that Nadine will continue on a similar heading and speed for the next 24 h or so, before turning toward the west as it weakens. The NHC forecast has been nudged to the southwest at most forecast points, and is generally near the HFIP Corrected Consensus. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 14.5N 34.9W 45 KT 50 MPH 12H 12/0600Z 14.9N 36.0W 40 KT 45 MPH 24H 12/1800Z 15.5N 37.7W 35 KT 40 MPH 36H 13/0600Z 15.7N 40.0W 30 KT 35 MPH 48H 13/1800Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Sergio Forecast Discussion Number 50

2018-10-11 22:37:44| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Thu Oct 11 2018 000 WTPZ41 KNHC 112037 TCDEP1 Tropical Storm Sergio Discussion Number 50 NWS National Hurricane Center Miami FL EP212018 200 PM PDT Thu Oct 11 2018 The cloud pattern of Sergio consists of a large and vigorous swirl of low clouds with a few patches of deep convection within a band in the northern semicircle. In fact, the cloud pattern on satellite resembles a cyclone that has begun to acquire extratropical characteristics. Convection has decreased, and Dvorak numbers now support a lower initial intensity of 50 kt. Sergio's circulation is already over cooler waters and the shear is increasing, so weakening should continue from now on. Sergio, however, is expected to still be a tropical storm when it moves over the Baja California peninsula on Friday. Thereafter, it should weaken faster while interacts with the high terrain and then reach the state of Sonora as a tropical depression followed by dissipation. Sergio has increased its forward speed and is now moving toward the northeast at about 20 kt. Since the steering currents are not expected to change, the general motion should continue until dissipation in about 36 hours os so. Track models continue to be in excellent agreement, and unanimously bring the core of Sergio over the central portion of the Baja California peninsula in a little more than 12 hours and so does the official forecast. 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 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 11/2100Z 23.5N 116.7W 50 KT 60 MPH 12H 12/0600Z 25.5N 114.3W 45 KT 50 MPH 24H 12/1800Z 28.5N 110.5W 30 KT 35 MPH...INLAND 36H 13/0600Z 31.0N 107.5W 20 KT 25 MPH...POST-TROP/INLAND 48H 13/1800Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Michael Forecast Discussion Number 20

2018-10-11 16:49:14| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Thu Oct 11 2018 000 WTNT44 KNHC 111449 TCDAT4 Tropical Storm Michael Discussion Number 20 NWS National Hurricane Center Miami FL AL142018 1100 AM EDT Thu Oct 11 2018 Surface, radar, and satellite data indicate that the center of Michael has moved over central South Carolina this morning, and will be moving into central North Carolina shortly. Sustained winds near the center have decreased, but there have been a couple of reports of sustained 37 to 40 kt winds along and just off the coast of South Carolina within the outer circulation of the storm. It is assumed that these coastal observing sites have not sampled the strongest winds, so the initial intensity remains 45 kt for this advisory. Wind gusts of 40 to 50 kt have been common over central and eastern portions of South Carolina this morning. As Michael's circulation emerges over the western Atlantic, little change in strength is expected today, with the highest sustained winds spreading northward along the coasts of South and North Carolina. Late tonight, Michael will quickly transform into an extratropical cyclone, and the global models indicate that the post-tropical low will quickly strengthen after moving offshore of the Mid-Atlantic coast. The post-tropical portion of Michael's intensity forecast is based on guidance from the NOAA Ocean Prediction Center. The storm is moving quickly northeastward or 050 degrees at 20 kt. Michael will continue to accelerate northeastward to east- northeastward as it moves over the western and north Atlantic during the next couple of days. There has been little change to the guidance envelope, and the new NHC track is an update of the previous advisory. Gale- to storm-force winds are expected over portions of the Mid-Atlantic coast as Michael exits the U.S. east coast and becomes post-tropical. Non-tropical high wind watches, warnings, and advisories have been issued by local NWS offices for wind hazards in these areas north of Duck, North Carolina. Key Messages: 1. Heavy rainfall from Michael could produce life-threatening flash flooding today over portions of the Carolinas and southeastern Virginia. 2. Tropical storm force wind gusts will continue across much of South Carolina and central and eastern North Carolina, with sustained tropical storm force winds expected along the coast of the Carolinas. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 34.7N 80.8W 45 KT 50 MPH...INLAND 12H 12/0000Z 36.6N 77.3W 45 KT 50 MPH...INLAND 24H 12/1200Z 39.3N 71.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 13/0000Z 42.8N 61.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 13/1200Z 45.5N 49.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 14/1200Z 48.2N 23.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 15/1200Z 49.0N 9.0W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 16/1200Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Nadine Forecast Discussion Number 10

2018-10-11 16:46:44| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Thu Oct 11 2018 000 WTNT45 KNHC 111446 TCDAT5 Tropical Storm Nadine Discussion Number 10 NWS National Hurricane Center Miami FL AL152018 1100 AM AST Thu Oct 11 2018 Nadine is strongly sheared and the low-level center of the tropical storm is now completely exposed, nearly 50 n mi to the southwest of the nearest deep convection. Satellite intensity estimates have decreased since last night, so the intensity has been lowered to 50 kt. This value is still on the high side of the available intensity estimates, but Nadine's intensity has generally been near the top of the intensity estimates for the past few days. Steady weakening is still anticipated because the shear is forecast by all models to increase further during the next day or two. By 72 h, if not sooner, all of the dynamical models forecast that Nadine will have lost its deep convection and degenerated into a trough of low pressure. No significant changes were made to the NHC intensity forecast. Nadine is still moving northwestward at 7 kt. Since Nadine's surface circulation has become completely exposed and the vortex is likely becoming very shallow, a quicker turn toward the west-northwest and west is now shown in the official track forecast. The track forecast has therefore been adjusted toward the southwest at most forecast times, but is still close to HCCA and TVCN through the short forecast period. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 14.1N 34.0W 50 KT 60 MPH 12H 12/0000Z 14.8N 34.9W 40 KT 45 MPH 24H 12/1200Z 15.5N 36.3W 35 KT 40 MPH 36H 13/0000Z 15.9N 38.0W 35 KT 40 MPH 48H 13/1200Z 16.2N 40.2W 30 KT 35 MPH 72H 14/1200Z...DISSIPATED $$ Forecaster Zelinsky

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