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Hurricane Laura Forecast Discussion Number 31

2020-08-27 16:48:40| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Thu Aug 27 2020 000 WTNT43 KNHC 271448 TCDAT3 Hurricane Laura Discussion Number 31 NWS National Hurricane Center Miami FL AL132020 1000 AM CDT Thu Aug 27 2020 Laura has continued to move inland over west-central Louisiana this morning. Satellite and radar imagery has shown a gradual filling of the eye, and a reduction in Doppler velocities in the northeastern eyewall. The initial intensity is set at 65 kt, based on a reduction of the Doppler velocities and the typical filling rate of inland hurricanes. The highest wind gusts at official observing sites within the past few hours has been at Alexandria, Louisiana, where a gust to 75 kt has been reported. The hurricane is moving slightly east of due north or 005/14 kt. A general northward motion should continue through this evening as the hurricane moves around the western portion of a mid-level ridge over the southeastern United States. Laura should turn northeastward overnight while it moves across Arkansas and becomes embedded within the mid-latitude westerlies. A faster east-northeastward motion is forecast by late Friday, which will bring Laura or its remnants across the central Appalachians and to the Mid-Atlantic states on Saturday. After that time, the system is expected to accelerate east-northeastward to northeastward over the western Atlantic. Laura will continue to rapidly weaken today while it moves farther inland. The cyclone will become a tropical storm this afternoon and is expected to weaken to a tropical depression tonight or early Friday. Although Laura is weakening, strong wind gusts are likely to spread over northern Louisiana and Arkansas into this evening. The UKMET and ECMWF models continue show the extratropical remnants of Laura strengthening somewhat over the western Atlantic, and the NHC forecast continues to depict the system as a gale-force low at days 3-5. An alternate scenario is for the system to be absorbed by a frontal boundary over the western Atlantic before the end of the forecast period. The extratropical portion of the forecast is based on guidance from the NOAA Ocean Prediction Center. Key Messages: 1. Dangerous storm surge will result in elevated water levels for the next few hours along the Gulf Coast from Sabine Pass, Texas, to Port Fourchon, Louisiana. In some areas where surge penetrated far inland, flood waters will not fully recede for several days. 2. Damaging winds will continue near the center of Laura over portions of northern Louisiana and Arkansas today and this evening. 3. Widespread flash flooding along small streams, urban areas, and roadways will continue across portions of Louisiana, Mississippi, and Arkansas. Additional rainfall will also lead to minor to moderate freshwater river flooding. The heavy rainfall threat and flash and urban flooding potential will spread northeastward into the middle-Mississippi, lower Ohio and Tennessee Valleys, and Mid-Atlantic States Friday and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 31.9N 93.1W 65 KT 75 MPH 12H 28/0000Z 33.9N 92.7W 40 KT 45 MPH...INLAND 24H 28/1200Z 35.8N 91.2W 30 KT 35 MPH...INLAND 36H 29/0000Z 37.0N 87.7W 25 KT 30 MPH...INLAND 48H 29/1200Z 38.0N 82.1W 25 KT 30 MPH...POST-TROP/INLAND 60H 30/0000Z 38.7N 74.9W 30 KT 35 MPH...POST-TROP/INLAND 72H 30/1200Z 41.8N 66.7W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 31/1200Z 50.0N 53.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 01/1200Z 53.5N 43.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Storm Hernan Forecast Discussion Number 6

2020-08-27 16:48:10| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Thu Aug 27 2020 000 WTPZ43 KNHC 271448 TCDEP3 Tropical Storm Hernan Discussion Number 6 NWS National Hurricane Center Miami FL EP132020 900 AM MDT Thu Aug 27 2020 First light visible satellite imagery reveals that Hernan remains a sheared tropical cyclone with most of the deep convection confined to the western semicircle. Even though convection has waned a bit overnight, there appears to be a new cluster developing. Therefore the initial intensity is being held at 40 kt, based on the earlier morning ASCAT overpass. Hernan should at least maintain its current strength for the next 12-24 h as it remains over very warm waters while battling moderate easterly shear. This shear is not forecast to abate during the forecast period. And after 24 h, the cyclone is expected to begin moving over progressively cooler waters. The combination of these two factors should induce a weakening trend. By 60 h, simulated satellite imagery by global models suggest that the cyclone will become devoid of deep convection. After that time, the remnant low is expected to be absorbed within the broader circulation of Hernan to its west. The latest NHC intensity forecast is close to the IVCN/ICON intensity consensus. Hernan has turned to the north-northwest and is moving at about 4 kt. There is no change to the track forecast reasoning. Hernan is expected to remain caught within a large-scale, eastern North Pacific cyclonic gyre during the next few days, which will result in Hernan moving counter-clockwise around the eastern and northern periphery of the gyre. The cyclone will continue to parallel the coast of southwestern Mexico through this evening, followed by a northwestward then westward turn tonight and Friday. The westward motion should continue until the system becomes absorbed early next week. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 19.1N 106.2W 40 KT 45 MPH 12H 28/0000Z 20.1N 107.0W 40 KT 45 MPH 24H 28/1200Z 21.2N 108.5W 35 KT 40 MPH 36H 29/0000Z 22.2N 110.2W 30 KT 35 MPH 48H 29/1200Z 22.8N 112.3W 30 KT 35 MPH 60H 30/0000Z 22.5N 113.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 30/1200Z...ABSORBED $$ Forecaster Latto

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Tropical Storm Iselle Forecast Discussion Number 4

2020-08-27 10:50:08| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Thu Aug 27 2020 000 WTPZ44 KNHC 270849 TCDEP4 Tropical Storm Iselle Discussion Number 4 NWS National Hurricane Center Miami FL EP142020 200 AM PDT Thu Aug 27 2020 A sheared band of deep convection has persisted near and to the southwest and west of Iselle's center. Night-visible satellite imagery indicates that the circulation has tightened up somewhat, and the latest UW-CIMSS SATCON intensity estimate is 41 kt. Based on these satellite data, the initial intensity has been increased to 40 kt. Unfortunately, all three scatterometer passes missed Iselle's inner-core wind field. The initial motion estimate is 030/04 kt. Similar to Tropical Storm Hernan farther to the east, Iselle is forecast to remain embedded within a large monsoon gyre, which will gradually contract down as Hernan moves toward southern Baja California and weakens over the next few days. This will result in the current southwesterly flow on the south side of Iselle to become more southerly, which will gradually turn the cyclone northward and then northwestward. By 72 hours, Iselle is expected to interact with and possibly absorb the remnants of Hernan when the two systems are west-southwest of Baja California. Thereafter, Iselle is forecast to move westward to west-southwestward and slowly weaken. The new NHC forecast track is close to a blend of the HCCA corrected-consensus model and the simple consensus models GFEX and TVCE, and is similar to the previous advisory track. Although short-lived convective bursts near the center will likely continue for the next few days, no significant strengthening is forecast for the next 48 hours due to moderate-to-strong easterly vertical wind shear that will persist across the system. At 60 hours and beyond, strong shear is expected to gradually weaken Iselle, with degeneration into a post-tropical remnant low forecast to occur by day 4, with the cyclone possibly even dissipating by 120 hours. The NHC intensity forecast is similar to the previous advisory, and closely follows the IVCN intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 16.6N 116.1W 40 KT 45 MPH 12H 27/1800Z 17.2N 115.7W 40 KT 45 MPH 24H 28/0600Z 17.8N 115.2W 40 KT 45 MPH 36H 28/1800Z 18.4N 114.6W 40 KT 45 MPH 48H 29/0600Z 19.3N 114.1W 40 KT 45 MPH 60H 29/1800Z 20.5N 113.9W 35 KT 40 MPH 72H 30/0600Z 21.7N 114.6W 35 KT 40 MPH 96H 31/0600Z 22.4N 115.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 01/0600Z 22.4N 117.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Tropical Storm Hernan Forecast Discussion Number 5

2020-08-27 10:43:10| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Thu Aug 27 2020 000 WTPZ43 KNHC 270842 TCDEP3 Tropical Storm Hernan Discussion Number 5 NWS National Hurricane Center Miami FL EP132020 300 AM MDT Thu Aug 27 2020 Although Hernan is a sheared tropical cyclone, another strong burst of deep convection with cloud tops of -83C to -86C has developed near and south through west of the center. An 0401Z ASCAT-A scatterometer pass revealed several 38-40 kt surface wind vectors of south through southwest of the center, so the initial intensity has been increased to 40 kt, which is supported by a recent UW-CIMSS SATCON estimate of 40 kt. The initial motion is estimate is 355/04 kt. Hernan is expected to remain caught within a large-scale, eastern North Pacific cyclonic gyre during the next few days, which will result in Hernan moving counter-clockwise around the eastern and northern periphery of the gyre. The cyclone will continue to move slowly northward this morning, followed by a turn toward the northwest by Thursday afternoon, with a west-northwestward motion expected on Friday. By Saturday, Hernan is forecast to degenerate into a remnant low pressure system, and possibly even dissipate and merge with Tropical Storm Iselle when the two systems are west-southwest of Baja California. The new NHC track is a very similar to the previous advisory track, and lies close to a blend of the simple track consensus models TVCE and GFEX, and the NOAA-HCCA corrected-consensus model. Hernan will remain in a moderate-to-strong easterly vertical wind shear regime for the next three days, which is expected to prevent any significant strengthening from occurring despite the cyclone being over warm waters and within a moist mid-level environment. By 60 hours, Hernan is forecast to degenerate into a remnant low, and possibly merge with Tropical Storm Iselle in 72-96 hours. The official intensity forecast is similar to the IVCN intensity consensus model. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 18.6N 106.0W 40 KT 45 MPH 12H 27/1800Z 19.5N 106.2W 40 KT 45 MPH 24H 28/0600Z 20.7N 107.3W 40 KT 45 MPH 36H 28/1800Z 21.9N 108.8W 35 KT 40 MPH 48H 29/0600Z 22.7N 110.8W 30 KT 35 MPH 60H 29/1800Z 22.7N 112.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 30/0600Z 22.4N 114.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 31/0600Z...DISSIPATED $$ Forecaster Stewart

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Hurricane Laura Forecast Discussion Number 30

2020-08-27 10:42:38| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Thu Aug 27 2020 763 WTNT43 KNHC 270842 TCDAT3 Hurricane Laura Discussion Number 30 NWS National Hurricane Center Miami FL AL132020 400 AM CDT Thu Aug 27 2020 Laura made landfall near Cameron, Louisiana, around 0600 UTC (1 am CDT) with maximum sustained winds of 130 kt, which is near the high end of category 4 status. At the time of landfall, Laura was a ferocious looking hurricane with a clear circular eye, an intense eyewall, and tightly-coiled surrounding spiral bands. Since the powerful hurricane has been inland for a few hours, there has been some decrease in winds, and the estimated initial wind speed based on Doppler radar data, surface observations, and guidance from an inland decay model is 105 kt. The hurricane is now moving northward with the initial motion estimated to be 355/13 kt. Laura is expected to continue moving northward through tonight, which should take the core of the system across Louisiana and Arkansas. After that, Laura will likely become embedded in the mid-latitude westerlies, and the much weaker cyclone is forecast to move quickly east-northeastward across the southeast U.S. and the mid-Atlantic states on Friday and Saturday. By late in the weekend and early next week, Laura, or its extratropical remnants, should accelerate northeastward across the western Atlantic. Now that Laura is inland, rapid weakening is forecast and it will likely become a tropical storm later today and a tropical depression on Friday. It should be noted that strong hurricanes like Laura are not just coastal events. Even though Laura's highest winds will decrease quickly as it treks inland, significant impacts from heavy rains and strong wind gusts are likely through at least tonight across portions of Louisiana and Arkansas. Some strengthening as an extratropical cyclone is expected when the storm moves over the Atlantic waters late this weekend and early next week. Key Messages: 1. Unsurvivable storm surge with large and destructive waves will cause catastrophic damage from Sea Rim State Park, Texas, to Intracoastal City, Louisiana, including Calcasieu and Sabine Lakes. This surge could penetrate up to 40 miles inland from the immediate coastline, and flood waters will not fully recede for several days after the storm. 2. Hurricane-force winds will continue this morning in portions of the hurricane warning area, with catastrophic wind damage expected near Laura's eyewall. Hurricane-force winds and widespread damaging wind gusts will continue to spread well inland into portions of extreme eastern Texas and western Louisiana through the day. 3. Widespread flash flooding along small streams, urban areas, and roadways is expected across portions of Louisiana, Mississippi, and Arkansas. This will also lead to minor to moderate freshwater river flooding. The heavy rainfall threat and flash and urban flooding potential will spread northeastward into the middle-Mississippi, lower Ohio, Tennessee Valley, and Mid-Atlantic States Friday and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 30.5N 93.4W 105 KT 120 MPH...INLAND 12H 27/1800Z 32.6N 93.2W 65 KT 75 MPH...INLAND 24H 28/0600Z 34.8N 92.2W 40 KT 45 MPH...INLAND 36H 28/1800Z 36.5N 90.1W 30 KT 35 MPH...INLAND 48H 29/0600Z 37.6N 85.4W 25 KT 30 MPH...INLAND 60H 29/1800Z 38.2N 78.9W 30 KT 35 MPH...POST-TROP/INLAND 72H 30/0600Z 39.8N 71.4W 40 KT 45 MPH...POST-TROP/EXTRATROP 96H 31/0600Z 47.9N 55.9W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 01/0600Z 53.1N 46.8W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi/Zelinsky

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