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Tropical Depression Selma Forecast Discussion Number 6

2017-10-28 16:43:55| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Sat Oct 28 2017 000 WTPZ45 KNHC 281443 TCDEP5 Tropical Depression Selma Discussion Number 6 NWS National Hurricane Center Miami FL EP202017 1000 AM CDT Sat Oct 28 2017 The surface circulation center of Selma continues to move inland over San Salvador since making landfall just a couple of hours ago. Conventional imagery, radar data, and surface observations indicate that Selma has weakened during the past few hours and the initial intensity has been lowered to 30 kt for this advisory. Further weakening is forecast today, and Selma should quickly dissipate over the Sierra Madre Mountains tonight. Selma should turn northeastward soon and continue on this general motion until dissipation tonight, and the global models remain in agreement in this forecast philosophy. The primary threat associated with Selma is heavy rainfall with 2 to 5 inches that could cause flash floods in higher terrain over portions of El Salvador and Guatemala. Gusty winds to tropical-storm-force are also possible today. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 13.7N 88.5W 30 KT 35 MPH...INLAND 12H 29/0000Z 14.4N 87.6W 15 KT 15 MPH...POST-TROP/INLAND 24H 29/1200Z...DISSIPATED $$ Forecaster Roberts

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Potential Tropical Cyclone Eighteen Forecast Discussion Number 3

2017-10-28 10:39:26| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sat Oct 28 2017 000 WTNT43 KNHC 280839 TCDAT3 Potential Tropical Cyclone Eighteen Discussion Number 3 NWS National Hurricane Center Miami FL AL182017 500 AM EDT Sat Oct 28 2017 Scatterometer data from several hours ago indicated that the disturbance consists of a broad circulation with a 100-150 n mi wide area of light winds (less than 10 kt) and an equally as large radius of maximum winds. The system still does not appear to have a well-defined center of circulation, and in fact, the ASCAT data also showed that the maximum winds are down to about 30 kt. The associated deep convection is rather disorganized but has been increasing in coverage near the estimated center during the past few hours. While the exact center is difficult to locate, the disturbance's circulation appears to be moving just east of due north, or 010/9 kt. The disturbance is beginning to accelerate in the flow ahead of a deep-layer trough located over the eastern three-quarters of the United States, and this pattern is expected to cause the system to turn northeastward and accelerate further during the next couple of days. Although the track models are in agreement on this general scenario, the overall guidance envelope has shifted a little westward, most likely as a result of a repositioning of the disturbance's current location. The new NHC forecast has therefore been nudged westward as well, lying closest to HCCA and TVCA models through 36 hours. The disturbance is currently located in its best environment shear-wise, but the system's broad and elongated structure is likely delaying intensification. Although the shear will be increasing, it should remain low enough for the next 12-18 hours to support some strengthening if the circulation can tighten up. In addition, upper-level divergence is expected to increase, which should also support some strengthening. Since the disturbance has such a broad circulation, the NHC intensity forecast closely follows the intensity trends of the GFS and is not too different from the previous advisory. The system is now expected to merge with a cold front and be extratropical by 48 hours and then dissipate by 72 hours. Even though the track forecast has shifted a little closer to South Florida and the Florida Keys, the strongest winds are expected to be well to the east and southeast of the center over the Atlantic waters and the Bahamas. Therefore, tropical storm watches or warnings do not appear necessary for Florida at this time. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 19.6N 84.2W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 28/1800Z 21.7N 82.9W 35 KT 40 MPH...TROPICAL CYCLONE 24H 29/0600Z 24.9N 80.1W 40 KT 45 MPH 36H 29/1800Z 28.7N 76.5W 45 KT 50 MPH 48H 30/0600Z 34.2N 71.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 72H 31/0600Z...DISSIPATED $$ Forecaster Berg

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Potential Tropical Cyclone Eighteen Forecast Discussion Number 2

2017-10-28 04:40:58| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Fri Oct 27 2017 000 WTNT43 KNHC 280240 TCDAT3 Potential Tropical Cyclone Eighteen Discussion Number 2 NWS National Hurricane Center Miami FL AL182017 1100 PM EDT Fri Oct 27 2017 Satellite imagery shows that the disturbance over the northwestern Caribbean Sea is gradually becoming better organized with increasing convective banding in the western semicircle. However, experimental shortwave infrared data from GOES-16 appear to show the presence of multiple low cloud swirls, and it is unclear if the definition of the center has improved to the point where the system has become a tropical cyclone. Thus, the disturbance remains a potential tropical cyclone at this time. There are no recent observations of the winds near the center, so the initial intensity remains 35 kt based on continuity from the previous advisory. The initial motion is an uncertain 005/6. A deep-layer trough and developing frontal low over the northeastern United States are expected to cause the disturbance to turn northeastward and accelerate during the next 24 h, with a fast motion toward the northeast continuing until the disturbance is absorbed by the mid-latitude system. The track guidance is generally in good agreement with this scenario, although there remains some cross-track spread due mainly to the uncertain center position. The new forecast track is similar to the previous track and is in best agreement with the HFIP Corrected Consensus model. Environmental conditions appear at least somewhat favorable for intensification during the next 48 h, with light to moderate shear and strong upper-level divergence over the system. After that time, the system is expected to be absorbed into the aforementioned mid-latitude system and become a trough rotating around the larger circulation. The new intensity forecast is nudged upward slightly from the previous forecast and now shows a peak intensity of 50 kt before absorption. However, the forecast lies at the lower edge of the intensity guidance, and if the system can develop a better- defined inner core it could strengthen more than currently forecast. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 18.2N 84.4W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 28/1200Z 20.1N 83.4W 40 KT 45 MPH 24H 29/0000Z 22.9N 81.1W 45 KT 50 MPH...INLAND 36H 29/1200Z 26.2N 77.4W 45 KT 50 MPH...OVER WATER 48H 30/0000Z 30.8N 73.0W 50 KT 60 MPH 72H 31/0000Z...ABSORBED BY EXTRATROPICAL LOW $$ Forecaster Beven

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Tropical Storm Selma Forecast Discussion Number 4

2017-10-28 04:35:54| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Fri Oct 27 2017 000 WTPZ45 KNHC 280235 TCDEP5 Tropical Storm Selma Discussion Number 4 NWS National Hurricane Center Miami FL EP202017 1000 PM CDT Fri Oct 27 2017 Selma has not become any better organized during the past several hours. The center of the tropical storm is partially exposed between a small curved band to its southeast and weakening convection to the west. Recent microwave data confirmed that Selma is a compact system, and the associated tropical-storm-force winds are estimated to extend no more than 40 n mi from the center. The initial intensity is held at 35 kt, in agreement with the latest Dvorak classification from TAFB. Satellite fixes indicate that Selma has moved northward to north-northeastward during the past 6 to 12 hours, and the storm lies a little to the east of the previous NHC track prediction. A general northward motion is expected overnight, and that should bring the center of Selma near the coast of El Salvador by Saturday morning. The new NHC track forecast has shifted to the east based on the initial position and motion, and it lies close to the consensus models. Little change in strength is likely while Selma approaches the coast. Once the storm moves inland, rapid weakening is expected and the system will likely dissipate over the rugged terrain of Central America by Saturday night. The primary threat associated with Selma is heavy rainfall, with accumulations possibly as high as 10 inches over portions of El Salvador and Guatemala. This rainfall could cause life-threatening flash floods and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 12.3N 89.0W 35 KT 40 MPH 12H 28/1200Z 13.4N 89.1W 35 KT 40 MPH...NEAR THE COAST 24H 29/0000Z 14.3N 88.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 29/1200Z...DISSIPATED $$ Forecaster Cangialosi

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Potential Tropical Cyclone Eighteen Forecast Discussion Number 1

2017-10-27 22:45:23| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Oct 27 2017 000 WTNT43 KNHC 272045 TCDAT3 Potential Tropical Cyclone Eighteen Discussion Number 1 NWS National Hurricane Center Miami FL AL182017 500 PM EDT Fri Oct 27 2017 Data from an Air Force Reserve Hurricane Hunter aircraft investigating the disturbance over the northwestern Caribbean Sea indicate that the system does not yet have a well-defined center. In fact, the aircraft data and satellite imagery suggest that there are multiple circulations embedded within a broader circulation at this time. Given the lack of a well-defined center, the system is not a tropical cyclone, but since tropical storm conditions are expected to affect Cuba and the northwestern Bahamas in the next 24 to 36 hours, advisories are being initiated on the system as a potential tropical cyclone at this time. The initial intensity is set to 35 kt based on aircraft data, with these winds found well south of the broad circulation center. However, NOAA buoy 42057 also reported a peak 1-minute wind of 31 kt earlier today. Aircraft data suggest that the central pressure is around 1006 mb. The system is situated in a low-shear environment and over warm waters, so some slow strengthening is expected in the first 24 hours before the system reaches Cuba. The official forecast follows the trend of the intensity consensus in showing a peak of around 45 kt at 36 and 48 hours before the system is absorbed by an approaching cold front in 60-72 hours. Given the lack of a well-defined center, the initial position is and the initial motion of 330/05 are highly uncertain. A faster northward motion should begin soon as the disturbance begins to recurve ahead of an approaching mid/upper-level trough moving into the southeastern United States. This trough should cause a faster northeastward acceleration at 24 through 48 hours. The track model guidance is in generally good agreement on the overall scenario, with more along than cross track spread. The NHC forecast leans toward a blend of the ECMWF and GFS models and is a little slower than the current multi-model consensus. Not surprisingly, given the disorganized initial state of the system, the track forecast uncertainty is larger than usual. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 17.5N 84.5W 35 KT 40 MPH...POTENTIAL TROP CYCLONE 12H 28/0600Z 19.1N 84.1W 35 KT 40 MPH...TROPICAL STORM 24H 28/1800Z 21.7N 82.4W 40 KT 45 MPH 36H 29/0600Z 24.6N 79.6W 45 KT 50 MPH 48H 29/1800Z 28.0N 75.5W 45 KT 50 MPH 72H 30/1800Z...ABSORBED $$ Forecaster Brennan

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