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Tropical Depression Ida Forecast Discussion Number 19
2021-08-30 22:38:06| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Mon Aug 30 2021 000 WTNT44 KNHC 302037 TCDAT4 Tropical Depression Ida Discussion Number 19 NWS National Hurricane Center Miami FL AL092021 400 PM CDT Mon Aug 30 2021 Ida has continued to weaken while moving farther inland over west-central Mississippi this afternoon. Recent observations indicate that the stronger winds seen this morning along the northern Gulf coast have now dropped below tropical storm strength, and Ida has become a tropical depression. Additional weakening should occur while Ida moves over northeastern Mississippi and the Tennessee Valley during the next 12 to 24 hours. Ida is forecast to become an extratropical cyclone over the eastern United States by late Wednesday, and it is likely to be absorbed within a frontal boundary over the western Atlantic by the end of the forecast period. Ida has turned northeastward and is now moving 020/8 kt. A mid- to upper-level trough approaching Ida from the west should cause the cyclone to move faster toward the northeast over the next couple of days. The latest runs of the dynamical models are in a bit better agreement regarding the forward speed of the Ida as it moves across the eastern U.S., and the NHC track forecast is again near the middle of the guidance envelope. Although Ida's winds have decreased, the threat of heavy rainfall and flooding will continue to spread inland over portions of the Tennessee and Ohio Valleys, the Central and Southern Appalachians and the Mid-Atlantic through Wednesday. This is the last advisory issued by the National Hurricane Center on Ida. Future information on this system can be found in Public Advisories issued by the Weather Prediction Center beginning at 10 PM CDT, under AWIPS header TCPAT4, WMO header WTNT34 KWNH, and on the web at http://www.wpc.ncep.noaa.gov. Key Messages: 1. Ida will continue to produce heavy rainfall tonight through Tuesday morning across portions of southeast Louisiana, Mississippi, and western Alabama, resulting in considerable flash and urban flooding and significant river flooding impacts. Rivers in the Lower Mississippi Valley will remain elevated into next week. As Ida moves inland, additional considerable flooding impacts are likely across portions of the Tennessee Valley, the Ohio Valley, and particularly in the Central and Southern Appalachians into the Mid-Atlantic through Wednesday. 2. In areas that experienced damage and power loss, individuals should use extreme caution during the recovery phase. Post-storm fatalities and injuries often result from heart attacks, heat exhaustion, accidents related to clean up and recovery, and carbon monoxide poisoning from improper generator use. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 32.6N 90.3W 30 KT 35 MPH...INLAND 12H 31/0600Z 33.6N 89.3W 25 KT 30 MPH...INLAND 24H 31/1800Z 34.8N 87.2W 25 KT 30 MPH...INLAND 36H 01/0600Z 36.3N 84.3W 20 KT 25 MPH...INLAND 48H 01/1800Z 38.0N 80.7W 20 KT 25 MPH...POST-TROP/INLAND 60H 02/0600Z 39.0N 77.0W 25 KT 30 MPH...POST-TROP/EXTRATROP 72H 02/1800Z 39.5N 74.2W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 03/1800Z 41.0N 67.9W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 04/1800Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Kate Forecast Discussion Number 11
2021-08-30 22:36:04| National Hurricane Center (Atlantic)
Issued at 500 PM AST Mon Aug 30 2021 988 WTNT45 KNHC 302035 TCDAT5 Tropical Storm Kate Discussion Number 11 NWS National Hurricane Center Miami FL AL102021 500 PM AST Mon Aug 30 2021 The low-level center of Kate is exposed in visible satellite imagery this afternoon. Its deep convection collapsed late this morning, and the sheared tropical cyclone is now only producing a small area of convection over 60 n mi east of its center. A partial 1321 UTC ASCAT-B pass still showed numerous 30-kt wind vectors in the eastern semicircle, even with little to no active convection. The initial intensity is conservatively lowered to 35 kt for this advisory. The subtropical jet stream across the central Atlantic will continue to impart strong west-northwesterly vertical wind shear on Kate during the next day or so. If the struggling tropical cyclone can survive these hostile conditions, some modest strengthening could occur later this week over warm SSTs of 28 deg C or so. However, the lack of mid-level moisture in the surrounding environment may limit convective development even under these more favorable conditions, and there is no guarantee that Kate will survive that long. In fact, simulated satellite imagery from the GFS and ECMWF suggest that Kate may continue to only produce sporadic bursts of convection over the next couple of days, which jeopardizes its chances of surviving through the week. The official NHC intensity forecast has been adjusted downward based on the latest guidance trends and the uncertainties discussed above. Minor fluctuations in intensity could occur over the next 24-36 h as convective pulsing causes the cyclone's intensity to hover around tropical-storm-force strength. Kate is moving a little faster toward the north, or 355/9 kt, within a weakness in the subtropical ridge. A northward motion is expected to continue through early Tuesday. The subtropical ridge is expected to become reestablished over the central Atlantic Tuesday night into Wednesday, which should turn Kate toward the northwest through midweek. Thereafter, Kate is forecast to accelerate northward or north-northeastward ahead of an approaching deep-layer trough that will move across the western Atlantic late this week. Assuming Kate is still around by day 5, the cyclone is forecast to become absorbed by a larger extratropical low near Atlantic Canada. FORECAST POSITIONS AND MAX WINDS INIT 30/2100Z 22.7N 50.9W 35 KT 40 MPH 12H 31/0600Z 23.7N 50.7W 30 KT 35 MPH 24H 31/1800Z 24.7N 50.7W 30 KT 35 MPH 36H 01/0600Z 25.8N 51.1W 35 KT 40 MPH 48H 01/1800Z 27.0N 52.1W 35 KT 40 MPH 60H 02/0600Z 28.4N 53.5W 40 KT 45 MPH 72H 02/1800Z 30.1N 54.7W 40 KT 45 MPH 96H 03/1800Z 34.5N 55.0W 40 KT 45 MPH 120H 04/1800Z...DISSIPATED $$ Forecaster Reinhart
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Tropical Storm Kate Forecast Discussion Number 10
2021-08-30 16:55:30| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Mon Aug 30 2021 000 WTNT45 KNHC 301455 TCDAT5 Tropical Storm Kate Discussion Number 10 NWS National Hurricane Center Miami FL AL102021 1100 AM AST Mon Aug 30 2021 Although strong upper-level westerly shear continues to plague the cyclone, its satellite presentation improved early this morning as its center moved closer to the edge of the convective cloud mass to its east. An ASCAT-A pass from 1100 UTC revealed an area of 30 to 40-kt winds in the eastern semicircle of the cyclone, with some slightly stronger winds possibly rain contaminated underneath the deep convection. Additionally, UW-CIMSS ADT objective estimates have risen to around 40 kt within the past few hours, and TAFB gave a T2.5/35 kt subjective Dvorak classification at 12 UTC. These data support upgrading the depression to Tropical Storm Kate. Its initial intensity is set at 40 kt for this advisory, although that could be a bit generous given recent satellite trends. A weakness in the subtropical ridge is allowing Kate to move just west of due north, or 355/7 kt. This general motion should continue for the next day or so before the subtropical ridge becomes reestablished over the central Atlantic Ocean. Thereafter, the cyclone should move northwestward on Wednesday and Thursday along the southwestern periphery of the ridge. By Friday, an approaching deep-layer trough should cause the cyclone to accelerate northward or north-northeastward through the rest of the forecast period. The track guidance has shifted a little left of the previous NHC track, and so the official forecast has been adjusted in that direction to bring it closer to the TVCA and HCCA consensus aids. The near-term intensity forecast is tricky, as the subtropical jet stream will maintain strong west-northwesterly shear over Kate during the next 24 to 36 h. In fact, recent satellite imagery of the cyclone shows the center is already more exposed than earlier this morning as the convection is waning. Kate is likely to continue exhibiting a bursting convective pattern over the next couple of days, which would likely result in some intensity fluctuations that hover around the tropical-storm-force threshold. The official NHC intensity forecast shows Kate as a 35-kt tropical storm during the first 36 h of the forecast. If Kate survives the hostile shear conditions, some modest intensification will be possible while the cyclone remains over 28 deg C waters. However, Kate will encounter a drier mid-level environment as it gains latitude, so significant strengthening does not appear likely at this time. The official intensity forecast is similar to the previous one beyond 48 h, as it shows only modest strengthening with time. By day 5, the global models suggest that Kate could be becoming absorbed by a larger extratropical low expected to form and deepen near Atlantic Canada. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 21.5N 50.9W 40 KT 45 MPH 12H 31/0000Z 22.3N 50.7W 35 KT 40 MPH 24H 31/1200Z 23.3N 50.5W 35 KT 40 MPH 36H 01/0000Z 24.3N 50.6W 35 KT 40 MPH 48H 01/1200Z 25.5N 51.5W 40 KT 45 MPH 60H 02/0000Z 26.9N 52.7W 40 KT 45 MPH 72H 02/1200Z 28.4N 54.2W 45 KT 50 MPH 96H 03/1200Z 32.0N 55.5W 50 KT 60 MPH 120H 04/1200Z 37.0N 53.4W 55 KT 65 MPH $$ Forecaster Reinhart
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Tropical Storm Ida Forecast Discussion Number 18
2021-08-30 16:54:31| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Mon Aug 30 2021 000 WTNT44 KNHC 301454 TCDAT4 Tropical Storm Ida Discussion Number 18 NWS National Hurricane Center Miami FL AL092021 1000 AM CDT Mon Aug 30 2021 The center of Ida has moved farther inland over western Mississippi this morning and NWS Doppler radar velocities and surface observations indicate that the tropical cyclone's winds have continued to decrease. The strongest winds are located in a band well southeast of the center along the coasts of Mississippi and Alabama where recent surface reports indicate 30-35 kt winds are still occurring. Therefore, the initial intensity is set at 35 kt. As Ida's circulation moves farther inland, additional weakening is expected and Ida is expected to become a tropical depression this afternoon. Continued weakening should occur while Ida moves over the Tennessee Valley on Tuesday, and the system is forecast to become extratropical over the eastern United States by late Wednesday. The global models indicate that the post-tropical cyclone will be absorbed by a frontal zone over the western Atlantic by the end of the forecast period. Ida is moving moving just east of due north or 010/8 kt. A north-northeastward turn should occur later today, followed by a faster northeastward motion tonight and Tuesday as a mid- to upper-level trough approaches the cyclone from the west. The dynamical model guidance remains tightly clustered with very little cross-track spread, although there remains some speed or along-track spread in the guidance. The NHC forecast is near the HCCA and TCVA consensus models. Key Messages: 1. Dangerous storm surge inundation will continue into this afternoon along portions of the coasts of Mississippi and Alabama. 2. Tropical storm force winds, especially in gusts, will continue over portions of southeastern Louisiana, southern Mississippi and southern Alabama this afternoon. 3. Ida will continue to produce heavy rainfall tonight through Tuesday morning across portions of southeast Louisiana, Mississippi, and western Alabama, resulting in considerable flash and urban flooding and significant river flooding impacts. Rivers in the Lower Mississippi Valley will remain elevated into next week. As Ida moves inland, additional considerable flooding impacts are likely across portions of the Tennessee Valley, the Ohio Valley, and particularly in the Central and Southern Appalachians into the Mid-Atlantic through Wednesday. 4. In areas that experienced damage and power loss, individuals should use extreme caution during the recovery phase. Post-storm fatalities and injuries often result from heart attacks, heat exhaustion, accidents related to clean up and recovery, and carbon monoxide poisoning from improper generator use. FORECAST POSITIONS AND MAX WINDS INIT 30/1500Z 31.9N 90.7W 35 KT 40 MPH...INLAND 12H 31/0000Z 33.1N 90.1W 30 KT 35 MPH...INLAND 24H 31/1200Z 34.5N 88.4W 25 KT 30 MPH...INLAND 36H 01/0000Z 35.8N 85.9W 20 KT 25 MPH...INLAND 48H 01/1200Z 37.5N 82.5W 20 KT 25 MPH...POST-TROP/INLAND 60H 02/0000Z 38.9N 78.7W 20 KT 25 MPH...POST-TROP/EXTRATROP 72H 02/1200Z 39.5N 75.7W 25 KT 30 MPH...POST-TROP/EXTRATROP 96H 03/1200Z 40.5N 70.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 04/1200Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Ida Forecast Discussion Number 17
2021-08-30 10:59:29| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Mon Aug 30 2021 000 WTNT44 KNHC 300859 TCDAT4 Tropical Storm Ida Discussion Number 17 NWS National Hurricane Center Miami FL AL092021 400 AM CDT Mon Aug 30 2021 Ida is now located well inland over southwestern Mississippi and weakening rapidly. However, Doppler velocity data from the Slidell, Louisiana, WSR-88D radar before it went down was still indicating velocity values near 90 kt between 4,000-4,500 ft, while the latest velocity data from Jackson, Mississippi, have been in the 70-75 kt range between 7,500 and 8,000 ft well east of the center. Thus, Ida will still be capable of producing damaging wind gusts in some of the stronger showers and thunderstorms for the next few hours. The intensity at 0600 UTC was 65 kt, which was based on a decay rate of about 10 kt per hour. A slightly slower decay rate of about 5 kt per hour has been used since then, which is the basis for the 50-kt advisory intensity at 0900 UTC. The estimated pressure of 990 mb is based on surface observation data, especially from McComb, Mississippi (KMCB), which has been reporting pressures near 995 mb with 25-30 kt of wind the past couple of hours. The initial motion estimate is now 355/07 kt. Ida should continue moving northward today around the western periphery of a deep-layer ridge situated over the southeastern United States. A faster motion toward the northeast is expected by Tuesday as a mid- to upper-level trough approaches the cyclone, with that motion continuing through the remainder of the week. The new NHC track forecast is just a tad to the south of the previous advisory, and lies down the middle off the tightly packed consensus models. Rapid weakening will continue as Ida moves farther inland over Mississippi due to land interaction and southwesterly vertical wind shear of more than 20 kt. However, damaging winds, especially in gusts, are expected to continue over southeastern Louisiana and southwestern Mississippi through through this morning. To account for this, the gust factor in the Forecast/Advisory has been adjusted accordingly. Ida is likely to weaken to a tropical depression this evening. Some slight restrengthening as an extratropical storm is possible when Ida moves over the western Atlantic in the day 4-5 period. In addition, heavy rains will spread northward and then northeastward along the forecast track. Key Messages: 1. Dangerous storm surge inundation will continue through this morning along portions of the coast between Grand Isle, Louisiana, to Bay St. Louis, Mississippi. Overtopping of local levees outside of the Hurricane and Storm Damage Risk Reduction System is possible where local inundation values may be higher. 2. Damaging winds, especially in gusts, will continue to spread inland near the track of Ida's center into southwestern Mississippi through this morning and early afternoon. These winds will likely lead to widespread tree damage and power outages. 3. Ida will continue to produce heavy rainfall tonight through Tuesday morning across portions of southeast Louisiana, coastal Mississippi, and southwestern Alabama resulting in considerable to life-threatening flash and urban flooding and significant riverine flooding impacts. As Ida moves inland, considerable flooding impacts are possible across portions of the Lower Mississippi Valley, Tennessee Valley, Ohio Valley, Central and Southern Appalachians, and Mid-Atlantic through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 31.0N 90.8W 50 KT 60 MPH...INLAND 12H 30/1800Z 32.2N 90.6W 30 KT 35 MPH...INLAND 24H 31/0600Z 33.7N 89.4W 25 KT 30 MPH...INLAND 36H 31/1800Z 35.1N 87.2W 25 KT 30 MPH...INLAND 48H 01/0600Z 36.6N 84.3W 20 KT 25 MPH...POST-TROP/INLAND 60H 01/1800Z 38.1N 80.8W 20 KT 25 MPH...POST-TROP/INLAND 72H 02/0600Z 39.0N 77.4W 25 KT 30 MPH...POST-TROP/EXTRATROP 96H 03/0600Z 40.1N 71.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 04/0600Z 40.5N 67.2W 30 KT 35 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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