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Hurricane Ida Forecast Discussion Number 8

2021-08-28 10:59:39| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Sat Aug 28 2021 000 WTNT44 KNHC 280859 TCDAT4 Hurricane Ida Discussion Number 8 NWS National Hurricane Center Miami FL AL092021 400 AM CDT Sat Aug 28 2021 Just after the last advisory, the convective structure of Ida got a bit ragged, probably due to the residual effects of land interaction with Cuba and a tongue of dry air that wrapped into the eastern side of the circulation. However, latest radar images from Cuba show that the eye is becoming better defined, and satellite imagery shows cooling of the cloud tops in the eyewall. The initial intensity has been held at 70 kt based on the latest trends and earlier Hurricane Hunter aircraft data. NOAA and Air Force reserve Hurricane Hunter aircraft are scheduled to investigate Ida again starting around 12Z. The initial motion remains northwestward or 315/14. A subtropical ridge centered off the southeast U.S. coast is expected to shift westward through the weekend, and this feature should continue to provide a steering flow that will take Ida steadily northwestward across the Gulf of Mexico during the next 36-48 h. The track guidance remains in good agreement that Ida will make landfall on the coast of southeastern or central Louisiana late Sunday or early Monday morning. After landfall, Ida is expected to turn northward through Louisiana and western Mississippi at a slower forward speed as it moves around the western end of the ridge. Recurvature into the westerlies and an east-northeastward motion are expected by the end of the forecast period. The new forecast track is nudged slightly to the west after 36 h to keep it near the various consensus models, but this is not a significant change from the previous forecast. Users are again reminded to not focus on the exact details of the track forecast as storm surge, wind, and rainfall impacts will extend far from the center. Ida is expected to remain in a favorable environment of light vertical shear and very warm sea-surface temperatures until it makes landfall. The only negative factor is the possibility that dry air may try to entrain into the system and slow the expected intensification. The SHIPS and LGEM models are showing a little less strengthening than previously. However, the HWRF and HMON models continue to forecast Ida to reach Category 4 intensity before landfall. The new intensity forecast will forecast a peak intensity of 120 kt in best agreement with the HWRF and HMON, and the pre-landfall part of the forecast is little changed from the previous forecast. After landfall, rapid weakening is expected due to land interaction, drier air, and an increase in shear, and Ida is expected to become a post-tropical cyclone as it moves through the Tennessee Valley. As Ida continues to intensify over the Gulf of Mexico, an expansion of its wind field is predicted. The NHC wind radii forecast is largely based on the radii consensus, and winds of at least tropical storm force are likely to reach the coast Sunday morning. Therefore, all preparations to protect life and property for this dangerous event need to be made today. Key Messages: 1. Hurricane and tropical storm conditions are ending over Cuba. However, Ida will continue to bring periods of heavy rain across western Cuba through today that may lead to flash flooding and mudslides. 2. There is a danger of life-threatening storm surge inundation Sunday along the coasts of Louisiana and Mississippi within the Storm Surge Warning area. Extremely life-threatening inundation of 10 to 15 feet above ground level is possible within the area from Morgan City, Louisiana, to the Mouth of the Mississippi River. Interests throughout the warning area should follow any advice given by local officials. 3. Ida is expected to be an extremely dangerous major hurricane when it reaches the coast of Louisiana. Hurricane-force winds are expected Sunday in portions of the Hurricane Warning area along the Louisiana coast, including metropolitan New Orleans, with potentially catastrophic wind damage possible where the core of Ida moves onshore. Actions to protect life and property should be rushed to completion in the warning area. 4. Ida is likely to produce heavy rainfall later Sunday into Monday across the central Gulf Coast from southeast Louisiana to coastal Mississippi resulting in significant flash and riverine flooding impacts. As Ida moves inland, flooding impacts are possible across portions of the Lower Mississippi and Tennessee Valleys. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 24.0N 85.2W 70 KT 80 MPH 12H 28/1800Z 25.4N 86.9W 85 KT 100 MPH 24H 29/0600Z 27.1N 88.9W 105 KT 120 MPH 36H 29/1800Z 28.6N 90.5W 120 KT 140 MPH 48H 30/0600Z 30.1N 91.3W 85 KT 100 MPH...INLAND 60H 30/1800Z 31.6N 91.2W 45 KT 50 MPH...INLAND 72H 31/0600Z 33.2N 90.5W 30 KT 35 MPH...INLAND 96H 01/0600Z 36.0N 87.0W 25 KT 30 MPH...INLAND 120H 02/0600Z 37.5N 82.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Tropical Depression Ten Forecast Discussion Number 1

2021-08-28 10:55:08| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Aug 28 2021 000 WTNT45 KNHC 280855 TCDAT5 Tropical Depression Ten Discussion Number 1 NWS National Hurricane Center Miami FL AL102021 500 AM AST Sat Aug 28 2021 The tropical wave and associated low pressure system that the NHC has been tracking for the past several days has finally acquired a well-defined surface circulation and enough organized deep convection to be classified as a tropical depression. The last few visible satellite images yesterday evening indicated a tight swirl in the low-cloud field and a 27/2325Z partial ASCAT-A pass showed the circulation was also well-defined, albeit with only 23-kt surface winds. Since the time of that scatterometer pass, however, a significant increase in deep convection with cloud tops colder than -80 deg C has developed very near and to the northeast of he center, with a few cells also now having developed just to the southwest of the center. Based on the structure noted in the ASCAT data and the pronounced increase in the amount and organization of the convection, the advisory intensity is estimated to be 30 kt. The initial motion estimate is 340/06 kt. The system has slowed down markedly during the past several hours, likely due to the sharp increase in the associated convection. A turn toward the north is forecast to begin later this afternoon as the system moves into a break in the Atlantic subtropical ridge pattern, with a general northward motion continuing through the remainder of the forecast period. The latest NHC model guidance is surprisingly in good agreement on this track scenario, with only minor forward speed differences noted between the models. The 18-20 kt of westerly vertical wind shear affecting the depression is expected to abate somewhat during the next 12-24 hours, which should allow for some slight strengthening to occur while the system moves over 27.5 deg C sea-surface temperatures. By 48 hours, however, the shear is forecast to increase again in excess of 25 kt, which should act to weaken the cyclone, possibly even causing it to degenerate into a remnant low. For now, however, the official intensity forecast calls for the system to remain a tropical depression at days 3 and 4 in the event the cyclone regenerates at day 5 when the shear is forecast to decrease below 10 kt, which may allow for convection to redevelop. The official intensity forecast closely follows a blend of the intensity consensus models IVCN and NOAA-HCCA. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 14.0N 49.9W 30 KT 35 MPH 12H 28/1800Z 14.8N 50.3W 35 KT 40 MPH 24H 29/0600Z 16.1N 50.3W 35 KT 40 MPH 36H 29/1800Z 17.7N 50.2W 35 KT 40 MPH 48H 30/0600Z 19.1N 50.0W 30 KT 35 MPH 60H 30/1800Z 20.7N 49.7W 30 KT 35 MPH 72H 31/0600Z 21.9N 49.7W 30 KT 35 MPH 96H 01/0600Z 24.5N 50.5W 30 KT 35 MPH 120H 02/0600Z 27.5N 52.8W 30 KT 35 MPH $$ Forecaster Stewart

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Tropical Storm Nora Forecast Discussion Number 10

2021-08-28 04:44:00| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Fri Aug 27 2021 000 WTPZ44 KNHC 280243 TCDEP4 Tropical Storm Nora Discussion Number 10 NWS National Hurricane Center Miami FL EP142021 1000 PM CDT Fri Aug 27 2021 Nora's cloud pattern has not become much better organized since earlier today. The central convection has diminished, but this is likely a diurnal fluctuation. Upper-level outflow appears to be fairly well-defined, with convective banding features most prominent over the southern portion of the circulation. Dvorak intensity estimates from both TAFB and SAB remain at 55 kt, so the advisory intensity will be held at that value for now. The storm has been moving a little to the east of the previous track over the past few hours, but the longer-term motion estimate is still northwestward, or 325/9 kt. Nora should move on a northwestward or north-northwestward heading for the next 2-3 days on the southwestern side of a mid-tropospheric anticyclone. Late in the forecast period, the cyclone is forecast to turn northward as the ridge to its north weakens. The official forecast track has been nudged just a bit to the east of the previous one during the next 72 hours or so, but not as far east as the latest dynamical model consensus, TVCE. Nora is expected to be in a moist, low-shear environment for the next few days, so the atmospheric conditions should favor intensification into a hurricane. Nonetheless, the majority of the intensity guidance does not show much strengthening beyond 24 hours, probably due to land interaction. The official intensity forecast shows gradual strengthening for the next couple of days or so, and is similar to the previous one. This is close to the LGEM guidance based on the ECMWF global model fields. It should be noted that there is significant uncertainty in the future strength of Nora because of the possible influence of land. Key Messages: 1. Nora is forecast to strengthen to a hurricane on Saturday while passing nearby the coasts of the Mexican states of Jalisco and Nayarit, and hurricane watches and tropical storm warnings are in effect for portions of that coastline. Interests in these areas should closely monitor the progress of Nora and subsequent updates to the forecast. 2.Heavy rain associated with Nora is expected across coastal sections of the Mexican states of Guerrero, Michoacan, Colima, and Jalisco, as well as Baja California Sur. Life-threatening flash flooding and mudslides are expected. 3. Nora is forecast to move over the Gulf of California as a hurricane early next week, bringing a risk of wind and rain impacts to portions of the Mexican states of Baja California Sur, Sinaloa, and Sonora. Given the above-average uncertainty in the forecast, it is still too soon to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 16.3N 105.1W 55 KT 65 MPH 12H 28/1200Z 17.6N 105.6W 60 KT 70 MPH 24H 29/0000Z 19.6N 106.2W 65 KT 75 MPH 36H 29/1200Z 21.6N 107.0W 70 KT 80 MPH 48H 30/0000Z 22.7N 107.9W 75 KT 85 MPH 60H 30/1200Z 23.6N 108.6W 80 KT 90 MPH 72H 31/0000Z 24.5N 109.3W 80 KT 90 MPH 96H 01/0000Z 26.5N 111.0W 70 KT 80 MPH 120H 02/0000Z 29.5N 111.5W 45 KT 50 MPH...INLAND $$ Forecaster Pasch

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Hurricane Ida Forecast Discussion Number 7

2021-08-28 04:40:48| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Fri Aug 27 2021 000 WTNT44 KNHC 280240 TCDAT4 Hurricane Ida Discussion Number 7 NWS National Hurricane Center Miami FL AL092021 1100 PM EDT Fri Aug 27 2021 Ida made landfall in the Cuban province of Pinar Del Rio around 2320 UTC with maximum sustained winds estimated to be around 70 kt. Radar data from Cuba indicate that the inner core of Ida has remained intact after its passage over western Cuba with a well-defined eye and relatively symmetric eyewall evident. In addition, satellite images show deep convection increasing in both intensity and coverage, a sign that Ida is strengthening. The Air Force Hurricane Hunters are currently investigating Ida and so far have found maximum 700 mb flight-level winds of 75 kt. Based on that data, the initial intensity is held at 70 kt. The hurricane is moving northwestward at about 13 kt. A subtropical ridge centered off the southeast U.S. coast is expected to shift westward through the weekend. This feature should continue to provide a steering flow that will take Ida steadily northwestward across the Gulf of Mexico during the next couple of days. The models remain in very good agreement and show Ida making landfall in Louisiana late Sunday or early Monday morning. After the storm moves inland, a decrease in forward speed and a turn to the north and then the northeast is predicted as Ida moves in the flow on the northwest and north sides of the ridge. Since the models are tightly clustered and because the steering flow is well pronounced, there is high confidence in the track forecast. The new NHC track forecast is very similar to the previous one and near the various consensus aids, which are often the most accurate models. Users are again reminded to not focus on the exact details of the track forecast as storm surge, wind, and rainfall impacts will extend far from the center. Ida is expected to remain in conducive conditions for intensification until it reaches the central Gulf coast. The global models show a very favorable upper-level wind pattern over the storm and abundant environmental moisture. These conducive atmospheric conditions combined with very warm Gulf of Mexico waters should allow Ida to rapidly intensify this weekend. In fact, it seems likely that Ida will pass over a warm eddy over the central Gulf of Mexico, where the ocean heat content is very high. All of the models show significant strengthening, but there is a fair amount of spread on how strong the hurricane will get. The NHC intensity forecast remains near the high end of the model guidance, and shows Ida becoming an extremely dangerous category 4 hurricane prior to reaching the coast. After landfall, rapid weakening is expected due to land interaction, drier air, and an increase in shear. As Ida continues to intensify over the Gulf of Mexico, an expansion of its wind field is predicted. The NHC wind radii forecast is largely based on the radii consensus, and winds of at least tropical storm force are likely to reach the coast Sunday morning. Therefore, all preparations to protect life and property for this dangerous event need to be made on Saturday. Key Messages: 1. Life-threatening storm surge and hurricane conditions are expected to continue for the next few hours in portions of western Cuba, including the Isle of Youth, where a Hurricane Warning is in effect. Life-threatening heavy rains, flash flooding and mudslides are expected across Jamaica, the Cayman Islands, and western Cuba, including the Isle of Youth. 2. There is a danger of life-threatening storm surge inundation Sunday along the coasts of Louisiana and Mississippi within the Storm Surge Warning area. Extremely life-threatening inundation of 10 to 15 feet above ground level is possible within the area from Morgan City, Louisiana, to the Mouth of the Mississippi River. Interests throughout the warning area should follow any advice given by local officials. 3. Ida is expected to be an extremely dangerous major hurricane when it reaches the coast of Louisiana. Hurricane-force winds are expected Sunday in portions of the Hurricane Warning area along the Louisiana coast, including metropolitan New Orleans, with potentially catastrophic wind damage possible where the core of Ida moves onshore. Actions to protect life and property should be rushed to completion in the warning area. 4. Ida is likely to produce heavy rainfall later Sunday into Monday across the central Gulf Coast from southeast Louisiana to coastal Mississippi and Alabama, resulting in considerable flash, urban, small stream, and riverine flooding impacts. As Ida moves inland, flooding impacts are possible across portions of the Lower Mississippi and Tennessee Valleys. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 23.0N 84.0W 70 KT 80 MPH 12H 28/1200Z 24.4N 85.6W 85 KT 100 MPH 24H 29/0000Z 26.1N 87.7W 105 KT 120 MPH 36H 29/1200Z 27.8N 89.6W 120 KT 140 MPH 48H 30/0000Z 29.2N 90.8W 110 KT 125 MPH...INLAND 60H 30/1200Z 30.7N 91.0W 60 KT 70 MPH...INLAND 72H 31/0000Z 32.3N 90.6W 35 KT 40 MPH...INLAND 96H 01/0000Z 34.9N 88.2W 25 KT 30 MPH...INLAND 120H 02/0000Z 36.8N 83.9W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Hurricane Ida Forecast Discussion Number 6

2021-08-27 22:49:28| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Aug 27 2021 000 WTNT44 KNHC 272049 TCDAT4 Hurricane Ida Discussion Number 6 NWS National Hurricane Center Miami FL AL092021 500 PM EDT Fri Aug 27 2021 Cuban radar data and reports from an earlier Air Force Reserve Hurricane Hunter mission indicate that Ida's inner core structure continued to improve after the release of the previous advisory package. An eye became apparent in radar imagery before the center reached the Isle of Youth, and the final fix from the Air Force Hurricane Hunter aircraft reported a closed 24-n-mi wide eye. The aircraft measured winds to support hurricane intensity shortly before 1800 UTC, and during the final northeast eyewall pass, and flight-level wind data support increasing the intensity to 70 kt, which is used as the initial intensity for this advisory. The upper-level outflow has expanded over all but the southwestern portion of the circulation, and the upper-level wind pattern is forecast to continue to improve overnight and early Saturday. Once Ida moves past western Cuba and into the southeastern Gulf of Mexico, it will be moving through a very favorable oceanic and atmospheric environment consisting of high ocean heat content waters, low vertical wind shear, and a moist low- to mid-level atmosphere. These conditions are likely to result in a period of rapid strengthening during the next 24 to 36 hours. In fact, with the higher initial wind speed, the intensity guidance has significantly increased this cycle, and the bulk of the guidance now brings Ida to category 4 intensity. The NHC forecast explicitly calls for rapid intensification during the next 24 to 36 hours, which is supported by several of the dynamical models, the LGEM model, and high probabilities of rapid intensification indicated by the SHIPS and DTOPS RI guidance. The NHC forecast is near the IVCN multi-model consensus aid, but is lower than HCCA and LGEM. It should be noted that some fluctuations in intensity are possible as Ida nears the northern Gulf coast due to possible eyewall replacement cycles. In addition to the expected increase in strength, the dynamical model guidance again calls for Ida's wind field to expand while it moves over the Gulf of Mexico. As a result, there is higher-than-normal confidence that a large and powerful hurricane will impact portions of the northern Gulf coast by late this weekend and early next week. Ida has wobbled a little right of the previous track, but the longer term motion continues to be northwestward or 320/13 kt. The steering currents remain well-established as a strong deep-layer ridge over the western Atlantic should continue to steer Ida northwestward across the Gulf this weekend. Ida will approach the western portion of the ridge after landfall, and this should result in a slower northward motion by day 3. After that time, a short-wave trough over the central United States is expected to cause the system to turn northeastward. The track guidance remains in remarkably good agreement through landfall along the northern Gulf coast, and there is higher-than-normal confidence in that portion of the track forecast. However, users are again reminded to not focus on the exact details of the track forecast as storm surge, wind, and rainfall impacts will extend far from the center. Key Messages: 1. Life-threatening storm surge and hurricane conditions are expected to continue through tonight in portions of western Cuba, including the Isle of Youth, where a Hurricane Warning is in effect. Life-threatening heavy rains, flash flooding and mudslides are expected across Jamaica, the Cayman Islands, and western Cuba, including the Isle of Youth. 2. There is a danger of life-threatening storm surge inundation Sunday along the coasts of Louisiana and Mississippi within the Storm Surge Warning area. Extremely life-threatening inundation of 10 to 15 feet above ground level is possible within the area from Morgan City, Louisiana, to the Mouth of the Mississippi River. Interests throughout the warning area should follow any advice given by local officials. 3. Ida is expected to be an extremely dangerous major hurricane when it reaches the coast of Louisiana. Hurricane-force winds are expected Sunday in portions of the Hurricane Warning area along the Louisiana coast, including metropolitan New Orleans, with potentially catastrophic wind damage possible where the core of Ida moves onshore. Actions to protect life and property should be rushed to completion in the warning area. 4. Ida is likely to produce heavy rainfall later Sunday into Monday across the central Gulf Coast from southeast Louisiana to coastal Mississippi and Alabama, resulting in considerable flash, urban, small stream, and riverine flooding impacts. As Ida moves inland, flooding impacts are possible across portions of the Lower Mississippi and Tennessee Valleys. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 22.1N 83.2W 70 KT 80 MPH 12H 28/0600Z 23.5N 84.8W 85 KT 100 MPH 24H 28/1800Z 25.3N 86.9W 105 KT 120 MPH 36H 29/0600Z 27.1N 89.0W 115 KT 130 MPH 48H 29/1800Z 28.6N 90.6W 120 KT 140 MPH 60H 30/0600Z 30.0N 91.3W 80 KT 90 MPH...INLAND 72H 30/1800Z 31.5N 91.1W 40 KT 45 MPH...INLAND 96H 31/1800Z 34.4N 89.3W 30 KT 35 MPH...INLAND 120H 01/1800Z 36.0N 86.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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