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Hurricane Lee Forecast Discussion Number 28

2017-09-25 04:33:11| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sun Sep 24 2017 000 WTNT44 KNHC 250232 TCDAT4 Hurricane Lee Discussion Number 28 NWS National Hurricane Center Miami FL AL142017 1100 PM AST Sun Sep 24 2017 Lee has been relatively steady state in intensity during the last several hours. The 10 n mi eye of the hurricane remains distinct, and although the convective pattern around the eye is fairly symmetric, the cloud tops are not very cold. The latest Dvorak intensity estimates are 4.5/77 kt from both TAFB and SAB, and ADT values from CIMSS at the University of Wisconsin are slightly higher at 4.7/82 kt. Based on these data, the initial wind speed is held at 80 kt. Recent ASCAT data confirms that Lee is a very compact hurricane, with tropical-storm-force winds extending only 30 n mi from the center. Although wind shear is expected to remain low near Lee during the next couple of days, the hurricane is likely to be over its own cool SST wake for part of that time. These marginal SSTs and dry air will likely cause the system to change little in strength during the next couple of days. Thereafter, much drier air, a sharp increase in shear, and a track toward colder water should cause weakening by the end of the forecast period. The NHC intensity forecast is identical to the previous one and in best agreement with the consensus models IVCN and HCCA. Lee has been drifting east-southeastward during the past 12 hours in the flow on the south side of a mid- to upper-level trough. The trough is expected to bypass Lee on Monday, allowing high pressure to build to the north of the cyclone. This change in the steering pattern should cause the hurricane to turn westward by Monday night and Tuesday. By mid-week, another trough is expected to approach the hurricane, and this one should cause the system to accelerate to the northeast over the central Atlantic. The NHC track forecast has been adjusted to the west of the previous one to come into better agreement with the latest guidance. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 31.1N 49.5W 80 KT 90 MPH 12H 25/1200Z 31.0N 49.4W 85 KT 100 MPH 24H 26/0000Z 30.7N 49.9W 85 KT 100 MPH 36H 26/1200Z 30.6N 51.2W 85 KT 100 MPH 48H 27/0000Z 30.8N 52.5W 80 KT 90 MPH 72H 28/0000Z 31.8N 54.1W 75 KT 85 MPH 96H 29/0000Z 34.7N 53.0W 70 KT 80 MPH 120H 30/0000Z 40.0N 46.5W 55 KT 65 MPH $$ Forecaster Cangialosi

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Hurricane Maria Forecast Discussion Number 35

2017-09-24 22:57:27| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sun Sep 24 2017 000 WTNT45 KNHC 242057 TCDAT5 Hurricane Maria Discussion Number 35 NWS National Hurricane Center Miami FL AL152017 500 PM EDT Sun Sep 24 2017 Recent reports from NOAA and Air Force Reserve Hurricane Hunter aircraft indicate that Maria's pressure has fallen a few millibars since this morning, but there has been little overall change in intensity. A blend of the flight-level and Stepped Frequency Radiometer Microwave Radiometer data yields an initial wind speed of around 90 kt. Maria will be traversing warm water and remain in a low shear environment during the next day or so, and some fluctuations in intensity are possible through Monday. After that time, Maria is forecast to move over cooler waters left over from Hurricane Jose. This is likely to result in gradual weakening, however Maria is forecast to maintain hurricane status through the entire forecast period. Maria is moving just west of due north or 350/8 kt. The hurricane is currently being steered north-northwestward to northward between a cut-off low over the southeastern U.S. and a subtropical ridge over the southwestern Atlantic. The forward motion of the hurricane should slow down over the next couple of days as a ridge builds to the north of the system over the northeastern United States. After 72 h, Maria should turn east-northeastward and begin to recurve as the deep-layer flow turns southwestward ahead of large mid-latitude trough that is forecast to move over the Great Lakes region by the end of the week. The latest runs of the dynamical models are fairly similar to the previous ones, with the ECMWF along the western side of the guidance and the GFS near the eastern edge. The NHC track is between these solutions, and lies west of the various consensus aids out of respect for the ECMWF and its ensemble mean. Since Maria is a large hurricane, the associated tropical-storm- force winds could reach a portion of the North Carolina in about 48 hours. As a result, a Tropical Storm Watch has been issued for a portion of the coast of North Carolina. KEY MESSAGES: 1. Maria is forecast to continue moving northward, paralleling the U.S. east coast, and it is likely that some direct impacts will occur along portions of the coast beginning Tuesday, and a Tropical Storm Watch has been issued for a portion of the coast of North Carolina. 2. Storm surge flooding especially along the sound side of the North Carolina Outer Banks is possible beginning Tuesday, and a Storm Surge Watch has been issued for a portion of the North Carolina Outer Banks. 3. Swells from Maria are increasing along the coast of the southeastern United States and are expected to reach the Mid- Atlantic coast today. These swells will likely cause dangerous surf and rip currents at beaches in these areas through much of the week. For more information, please monitor information from your local National Weather Service office at www.weather.gov. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 29.4N 73.0W 90 KT 105 MPH 12H 25/0600Z 30.3N 73.2W 90 KT 105 MPH 24H 25/1800Z 31.4N 73.4W 85 KT 100 MPH 36H 26/0600Z 32.5N 73.5W 80 KT 90 MPH 48H 26/1800Z 33.6N 73.6W 80 KT 90 MPH 72H 27/1800Z 35.0N 73.3W 75 KT 85 MPH 96H 28/1800Z 35.8N 71.0W 65 KT 75 MPH 120H 29/1800Z 37.5N 64.5W 65 KT 75 MPH $$ Forecaster Brown

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Tropical Storm Pilar Forecast Discussion Number 5

2017-09-24 22:53:27| National Hurricane Center (East Pacific)

Issued at 400 PM CDT Sun Sep 24 2017 000 WTPZ43 KNHC 242053 TCDEP3 Tropical Storm Pilar Discussion Number 5 NWS National Hurricane Center Miami FL EP182017 400 PM CDT Sun Sep 24 2017 Pilar continues this afternoon to be a problematic system. Fortunately, a 1426Z GPM 36 GHz image suggested that the system's center was very close to Cabo Corrientes at that time. This allowed for a somewhat better estimate of the initial position and motion (350 degrees at 7 kt). Pilar is being advected around a deep-layer ridge located over central Mexico. Despite the initial continued movement at around 7 kt this afternoon, the guidance insists that Pilar should soon slow down. The official forecast track is quite similar to the previous one, with a course along or just west of the coast of southwestern Mexico. Fortunately, the model guidance came into better agreement with the track prediction, though some of the model's trackers could not explicitly follow the weak vortex beyond a day or so into the future. Because of Pilar having some of its circulation over the high terrain of southwestern Mexico, some weakening has likely occurred. The initial intensity is reduced to 35 kt, based upon a blend of the TAFB and SAB Dvorak classifications. While the SSTs are warm and the vertical shear is only moderate for the day or so, continued interaction with land is likely to prevent any re-intensification. After about 24 hours, the vertical shear should go way up, as Pilar is affected by strong southerlies associated with a vigorous mid- to upper-tropospheric trough over the southwestern United States. The official intensity forecast is closest to a blend of the LGEM statistical scheme and the HWRF dynamical model, and is just slightly below the previous advisory. An alternative scenario is for Pilar to dissipate substantially sooner because of the land interactions. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 20.8N 105.8W 35 KT 40 MPH 12H 25/0600Z 21.8N 106.0W 35 KT 40 MPH 24H 25/1800Z 22.5N 106.2W 30 KT 35 MPH 36H 26/0600Z 23.0N 106.5W 25 KT 30 MPH 48H 26/1800Z 23.5N 107.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 27/1800Z...DISSIPATED $$ Forecaster Landsea

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Hurricane Lee Forecast Discussion Number 27

2017-09-24 22:32:10| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 24 2017 000 WTNT44 KNHC 242031 TCDAT4 Hurricane Lee Discussion Number 27 NWS National Hurricane Center Miami FL AL142017 500 PM AST Sun Sep 24 2017 Lee is displaying a 15 nm wide eye amidst a small central dense overcast. SAB, TAFB, Advanced Dvorak, and AMSU intensity estimates are all similar, indicating an initial maximum wind speed that remains 80 kt. The LGEM and DSHIPS statistical guidance shows continued hurricane intensity for the next several days because of low vertical shear and warm waters. However, the HWRF and COAMPS dynamical model output suggests quite a bit weaker system, perhaps because these models are anticipating that Lee will move over its own cold wake in a couple of days. By day 4 or 5, the environment should become hostile as cooler, drier air gets entrained into Lee and it experiences strong vertical shear from the outflow of Hurricane Maria. The official intensity forecast is in between the weaker dynamical models and the stronger previous advisory. The system is moving toward the southeast at about 3 kt. The hurricane should bend back toward the southwest and then west during the next couple of days as a mid-level ridge gets re-established north of Lee. By day 4 the system should recurve and accelerate toward the north-northeast or northeast, as it gets picked up by the mid-latitude westerlies. The track model consensus has shifted westward through day 3 and then accelerated faster toward the northeast by day 5. The official track forecast follows suit, using the HFIP Corrected Consensus Approach. Lee is a tiny hurricane. The 1236Z ASCAT pass showed that tropical storm-force-winds only extend outward at most 30 nm from the center. The global models indicate only a slightly larger hurricane over time and the official size forecasts are based upon the RVCN multi-model scheme. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 31.3N 49.7W 80 KT 90 MPH 12H 25/0600Z 31.0N 49.2W 85 KT 100 MPH 24H 25/1800Z 30.7N 49.1W 85 KT 100 MPH 36H 26/0600Z 30.3N 50.1W 85 KT 100 MPH 48H 26/1800Z 30.4N 51.5W 80 KT 90 MPH 72H 27/1800Z 31.0N 53.5W 75 KT 85 MPH 96H 28/1800Z 33.0N 53.0W 70 KT 80 MPH 120H 29/1800Z 37.0N 49.0W 55 KT 65 MPH $$ Forecaster Landsea

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Hurricane Lee Forecast Discussion Number 26

2017-09-24 16:49:55| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Sep 24 2017 000 WTNT44 KNHC 241449 TCDAT4 Hurricane Lee Discussion Number 26 NWS National Hurricane Center Miami FL AL142017 1100 AM AST Sun Sep 24 2017 The rapid intensification of Lee appears to have slowed for now. Lee has a well-defined 10 to 15 n mi wide eye, but the cloud tops surrounding the eye have not cooled since the previous advisory. Subjective and objective Dvorak T-numbers from TAFB, SAB, and UW/CIMSS all support 75 to 80 kt, and the initial intensity is set at 80 kt. The intensity forecast of the small hurricane is somewhat tricky. As mentioned in the previous discussion, Lee is forecast to remain in a low-shear environment for the next few days, but the slow motion of the hurricane is likely to cause upwelling and a decrease in sea surface temperatures beneath the hurricane. Although the intensity guidance is slightly lower this cycle, the new NHC forecast is similar to the previous advisory and brings Lee to near major hurricane strength within the next 24 to 36 hours. Late in the period decreasing sea surface temperatures and increasing shear should impart a weakening trend. Lee has turned southeastward. The track models are similar with the overall forecast scenario of Lee moving slowly southeastward today, then turning west-southwestward or westward late Monday and Tuesday as a high pressure ridge builds to the north and northwest of the hurricane. This ridge is forecast to weaken later in the week, with Lee turning northward, then northeastward ahead of Maria as the mid-latitude westerlies dip southward. There is a large bifurcation in the guidance models after about 48 hours, due to the location and timing of recurvature. The NHC track leans closer to the ECMWF and latest European ensemble mean, but the track forecast is of low confidence. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 31.4N 49.9W 80 KT 90 MPH 12H 25/0000Z 31.1N 49.4W 85 KT 100 MPH 24H 25/1200Z 30.7N 48.9W 95 KT 110 MPH 36H 26/0000Z 30.2N 49.2W 95 KT 110 MPH 48H 26/1200Z 30.1N 50.2W 95 KT 110 MPH 72H 27/1200Z 30.7N 51.8W 90 KT 105 MPH 96H 28/1200Z 32.2N 52.5W 85 KT 100 MPH 120H 29/1200Z 35.0N 50.5W 70 KT 80 MPH $$ Forecaster Brown

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