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Hurricane Laura Forecast Discussion Number 23

2020-08-25 17:05:38| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Tue Aug 25 2020 000 WTNT43 KNHC 251505 TCDAT3 Hurricane Laura Discussion Number 23 NWS National Hurricane Center Miami FL AL132020 1000 AM CDT Tue Aug 25 2020 Satellite imagery shows that Laura has become a little better organized since it crossed western Cuba, and it now has a central dense overcast and some outer banding in the southern quadrant. Reports from Air Force Reserve and NOAA Hurricane Hunter aircraft included SFMR winds of near 65 kt, 700-mb flight-level winds as high as 77 kt, and a central pressure near 990 mb. Based on these data, Laura has been upgraded to a hurricane with an initial intensity of 65 kt. The initial motion is west-northwestward or 290/14 kt. The hurricane is currently on the south side of a large-deep layer ridge over the southeastern United States, and it is moving toward a break in the ridge caused by mid- to -upper-level troughing over Texas and the southern Great Plains. The current and forecast synoptic pattern should steer Laura west-northwestward today followed by a turn toward the northwest tonight and toward the north by Wednesday night and Thursday. This will result in the hurricane making landfall in the area of southwestern Louisiana or the upper Texas coast late Wednesday night or Thursday morning. The new forecast track before landfall has been nudged a little to the west of the previous track in response to a westward nudge in the guidance. However, it still lies a little east of the consensus models at the time of landfall. After landfall, Laura is expected to recurve into the westerlies and move eastward through the Tennessee Valley and the mid-Atlantic States. The hurricane currently looks a little ragged, with little or no convection outside of the central dense overcast and the southern quadrant banding. This may be due to dry air in the vicinity and some light northerly shear. Conditions appear generally favorable for strengthening during the next 36 h, and the new intensity forecast calls for Laura to become a major hurricane during this time. The global model are in good agreement that the hurricane should encounter increasing shear in the last 12 h before landfall, although the potential impacts on the landfall intensity are unclear. After landfall, Laura should weaken through the 96 h point. After that, some re-intensification is expected as the storm becomes extratropical. Users are again reminded not to focus on the exact details of the track or intensity forecasts as the average NHC track error at 48 h is around 80 miles and the average intensity error is close to 15 mph. In addition, wind, storm surge, and rainfall hazards will extend far from the center. Key Messages: 1. Laura is forecast to reach the northwestern Gulf Coast at or near major hurricane intensity Wednesday night. Do not focus on the details of the official forecast given the typical uncertainty in NHC's track and intensity predictions. Storm surge, wind, and rainfall hazards will extend well away from Laura's center along the Gulf Coast. 2. There is the danger of life-threatening storm surge accompanied by large and dangerous waves from San Luis Pass, Texas, to the Mouth of the Mississippi River, including areas inside the Port Arthur Hurricane Flood Protection system. A Storm Surge Warning is in effect and residents should follow any advice given by local officials. Actions to protect life and property should be rushed to completion today, as water levels will begin to rise Wednesday. 3. Hurricane conditions are expected by Wednesday evening in the area from San Luis Pass, Texas, to west of Morgan City, Louisiana, and a Hurricane Warning is in effect. Tropical storm conditions are expected to begin in the warning area Wednesday afternoon. 4. The threat of widespread flash and urban flooding along with small streams overflowing their banks will be increasing Wednesday night into Thursday from far eastern Texas, across Louisiana, and Arkansas. This will also lead to minor to isolated moderate river flooding. The heavy rainfall threat will spread northeastward into the middle-Mississippi, lower Ohio, and Tennessee Valleys Friday and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 23.7N 87.0W 65 KT 75 MPH 12H 26/0000Z 24.6N 89.2W 75 KT 85 MPH 24H 26/1200Z 26.0N 91.5W 90 KT 105 MPH 36H 27/0000Z 28.0N 93.3W 100 KT 115 MPH 48H 27/1200Z 30.5N 93.9W 80 KT 90 MPH...INLAND 60H 28/0000Z 33.1N 93.6W 45 KT 50 MPH...INLAND 72H 28/1200Z 35.2N 92.1W 30 KT 35 MPH...INLAND 96H 29/1200Z 37.5N 83.5W 25 KT 30 MPH...INLAND 120H 30/1200Z 40.5N 69.5W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Tropical Storm Laura Forecast Discussion Number 22

2020-08-25 10:59:00| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Tue Aug 25 2020 000 WTNT43 KNHC 250858 TCDAT3 Tropical Storm Laura Discussion Number 22 NWS National Hurricane Center Miami FL AL132020 400 AM CDT Tue Aug 25 2020 Satellite images show that Laura is becoming better organized. Now that the center is clear from Cuba, very deep convection has developed into a ragged, pulsing central dense overcast, with a large curved band on the southern side of the circulation. The intensity is kept at 55 kt, matching the satellite estimates and a blend of the earlier flight-level and SFMR reconnaissance data. Hurricane Hunter missions from both the Air Force and NOAA should be in the storm within a couple hours to help obtain a new estimate. After a westward jog earlier, Laura is estimated to be moving west-northwestward again or 290/15. The synoptic situation consists over a large ridge near the southeastern United States and a weakness in the ridge over Central Texas due to an inverted trough. Laura should gradually gain latitude and turn to the northwest and north-northwest over the next two days while it is steered between those two features, move northward late this week through the southern United States, then move quickly eastward across the eastern U.S. over the weekend as it encounters the mid-latitude westerlies. The majority of the guidance has shifted a notable distance to the west on this run, perhaps due to a weaker trough over Texas and a more westward initial position of Laura (possibly due to persistent northerly mid-level shear). The new NHC prediction is at the eastern edge of the new guidance envelope since I don't want to bite off on such a large change on just one set of model runs. But since the storm has been tracking west of forecast expectations for quite some time, future westward track adjustments could be required later today. Laura is forecast to move over the very warm and deep waters of the Gulf of Mexico, with similar or lighter shear conditions through the next couple of days. Now that an inner core appears to be trying to form, conditions appear ripe for at least steady intensification, and rapid intensification is becoming more likely before landfall. In fact, almost all of the explicit guidance models, save the statistical-dynamical models, are showing a period of rapid strengthening at some point during the next couple of days. Thus, the new NHC forecast is higher than the last one, but not as high as the most of the regional hurricane models since shear could increase just before landfall. Users are again reminded not to focus on the exact details of the track or intensity forecasts as the average NHC track error at 48 h is around 80 miles and the average intensity error is close to 15 mph. In addition, wind, storm surge, and rainfall hazards will extend far from the center. Key Messages: 1. Laura is forecast to reach the northwestern Gulf Coast as a hurricane late Wednesday and early Thursday. Do not focus on the details of the official forecast given the typical uncertainty in NHC's 2-to-3 day track and intensity predictions. In addition, storm surge, wind, and rainfall hazards will extend well away from Laura's center along the Gulf Coast. 2. There is a risk of life-threatening storm surge from San Luis Pass, Texas, to Ocean Springs, Mississippi, within the next 48 hours, and a storm surge watch is in effect for these areas outside of the southeast Louisiana Hurricane and Storm Damage Risk Reduction System. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are possible by late Wednesday from San Luis Pass, Texas, to west of Morgan City, Louisiana, with tropical storm conditions possible by Wednesday afternoon, and a hurricane watch is in effect. Hurricane Warnings will likely be issued for a portion of that area later today. 4. The threat of widespread flash and urban flooding, along with small streams overflowing their banks, will be increasing Wednesday night into Thursday from far eastern Texas, across Louisiana, and Arkansas. This will also lead to minor-to-isolated moderate river flooding. The heavy rainfall threat will spread northeastward into the middle-Mississippi, lower Ohio and Tennessee Valleys Friday and Saturday. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 22.9N 85.7W 55 KT 65 MPH 12H 25/1800Z 23.8N 87.9W 65 KT 75 MPH 24H 26/0600Z 25.1N 90.6W 80 KT 90 MPH 36H 26/1800Z 26.8N 92.7W 95 KT 110 MPH 48H 27/0600Z 29.3N 93.7W 100 KT 115 MPH 60H 27/1800Z 32.1N 93.7W 55 KT 65 MPH...INLAND 72H 28/0600Z 34.5N 93.0W 30 KT 35 MPH...INLAND 96H 29/0600Z 37.0N 86.5W 25 KT 30 MPH...INLAND 120H 30/0600Z 39.0N 73.0W 40 KT 45 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake

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Post-Tropical Cyclone Marco Forecast Discussion Number 21

2020-08-25 10:40:09| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Tue Aug 25 2020 000 WTNT44 KNHC 250839 TCDAT4 Post-Tropical Cyclone Marco Discussion Number 21 NWS National Hurricane Center Miami FL AL142020 400 AM CDT Tue Aug 25 2020 Marco has been devoid of any significant convection for at least 12 hours, and ASCAT scatterometer surface wind data around 0239Z suggested that Marco might have degenerated in a north-to-south elongated trough. Based on this information, Marco has been downgraded to post-tropical remnant low. Brisk southwesterly vertical wind shear of 30 kt is forecast to increase to near 35 kt in 24 hours, which should prevent the redevelopment of deep convection near the center. Marco's remnants are expected to move generally westward along or just south of the southern coast of Louisiana for the next 24 hours or until dissipation occurs. This is the last forecast/advisory issued by the National Hurricane Center on Marco. Additional information on this system can be found in high seas forecasts issued by the national weather service...under AWIPS header NFDHSFAT1 and WMO header FZNT01 KWBC. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 28.8N 91.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 12H 25/1800Z 28.8N 92.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 26/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Laura Forecast Discussion Number 21

2020-08-25 04:45:24| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Mon Aug 24 2020 000 WTNT43 KNHC 250245 TCDAT3 Tropical Storm Laura Discussion Number 21 NWS National Hurricane Center Miami FL AL132020 1100 PM EDT Mon Aug 24 2020 Tropical Storm Laura made landfall on the Pinar del Rio province in western Cuba around 0000 UTC with maximum winds of about 55 kt. Around that time, a wind gust of 56 kt was reported in Havana. Since then the storm has moved across western Cuba and is now coming off the island and over the extreme southeastern Gulf of Mexico. Radar data from Cuba and satellite images indicate that the storm has become better organized with deep convection beginning to wrap around the center with persistent thunderstorms on the south side. Data from the NOAA and Air Force Hurricane Hunters indicate that the pressure has fallen to 996 mb and that the winds are around 55 kt. Laura continues to move fairly steadily to the west-northwest with the latest initial motion estimated to be 290/17 kt. The track forecast reasoning is generally unchanged from previous discussions. Laura should continue to move west-northwestward at about the same forward speed through Tuesday as it remains in the flow on the southwest side of the Atlantic subtropical ridge. By early Wednesday, Laura will likely slow down and turn northwestward and then northward as it moves into a break in the ridge, caused by a weak trough over the south-central U.S. This motion should cause the system to make landfall in either southwestern Louisiana or the Upper Texas coast Wednesday night or early Thursday. After landfall, Laura is forecast to continue moving northward before turning eastward on Friday as it becomes embedded in the mid-latitude westerlies. Although the global models are in relatively good agreement, there remains some spread in the ensemble members, especially in the ECMWF. Therefore, confidence in the track forecast is still not high. The NHC track forecast is slightly to the left of the previous one, trending toward the latest consensus aids. The storm is starting to pull away from the western portion of Cuba, and it should be over the warm Gulf of Mexico waters for about 2 days. Since Laura will have a notable amount of time over waters with high oceanic heat while moving through a low wind shear and high moisture air mass, significant strengthening seems quite likely until the storm makes landfall. The intensity models all show Laura making landfall as a hurricane, but there are differences on exactly how strong it will be. The NHC intensity forecast continues to stay near the consensus aids, which usually perform best, and Laura could be near major hurricane strengthen when it reaches the coast. Users are again reminded not to focus on the exact details of the track or intensity forecasts as the average NHC track error at 48 h is around 80 miles and the average intensity error is close to 15 mph. In addition, wind, storm surge, and rainfall hazards will extend far from the center. Key Messages: 1. Laura is forecast to reach the northwestern Gulf Coast as a hurricane late Wednesday and early Thursday. Do not focus on the details of the official forecast given the typical uncertainty in NHC's 2 to 3 day track and intensity predictions. In addition, storm surge, wind, and rainfall hazards will extend well away from Laura's center along the Gulf Coast. 2. There is a risk of life-threatening storm surge from San Luis Pass, Texas, to Ocean Springs, Mississippi, within the next 48 hours, and a storm surge watch is in effect for these areas outside of the southeast Louisiana Hurricane and Storm Damage Risk Reduction System. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are possible by late Wednesday from Port Bolivar, Texas, to west of Morgan City, Louisiana, with tropical storm conditions possible by Wednesday afternoon, and a hurricane watch is in effect. Additional hurricane watches may be needed farther south along the Texas coast if the track forecast shifts toward the south and west tonight and Tuesday. 4. Tropical storm conditions and heavy rainfall are expected across central and western Cuba for several more hours. These rains could cause mudslides and life-threatening flash and urban flooding. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 22.7N 84.0W 55 KT 65 MPH 12H 25/1200Z 23.7N 86.3W 65 KT 75 MPH 24H 26/0000Z 25.2N 89.1W 75 KT 85 MPH 36H 26/1200Z 26.8N 91.6W 85 KT 100 MPH 48H 27/0000Z 28.8N 93.0W 95 KT 110 MPH 60H 27/1200Z 31.3N 93.6W 65 KT 75 MPH...INLAND 72H 28/0000Z 33.8N 93.0W 40 KT 45 MPH...INLAND 96H 29/0000Z 36.7N 89.1W 25 KT 30 MPH...INLAND 120H 30/0000Z 36.9N 77.1W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Tropical Depression Marco Forecast Discussion Number 20

2020-08-25 04:31:54| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT Mon Aug 24 2020 000 WTNT44 KNHC 250231 TCDAT4 Tropical Depression Marco Discussion Number 20 NWS National Hurricane Center Miami FL AL142020 1000 PM CDT Mon Aug 24 2020 Visible imagery and surface observations indicated that Marco made landfall around 6 pm CDT near the mouth of the Mississippi River. Shortly before landfall, reports from an Air Force Reserve Hurricane Hunter plane indicated that Marco was still producing a small area of tropical-storm-force winds over water to the northeast of its center. Since then, the system has moved almost due west along the southeast coast of Louisiana while its deep convection has become farther displaced from the low-level center. Between the lack of central convection and Marco's proximity to land, it is likely that the winds have decreased since earlier this evening and the intensity has been lowered to 30 kt. If deep convection does not redevelop overnight, Marco will become a remnant low as soon as Tuesday morning. Regardless of its status, Marco should move generally westward near the coast of Louisiana while it weakens for the next day or so and could continue to produce heavy rain for portions of the north-central Gulf Coast tonight. The system is then forecast to dissipate by early Wednesday, if not sooner. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 29.0N 89.8W 30 KT 35 MPH 12H 25/1200Z 29.0N 91.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 26/0000Z 29.0N 93.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 26/1200Z...DISSIPATED $$ Forecaster Zelinsky

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