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Tropical Depression Eleven Forecast Discussion Number 2
2021-08-29 10:59:59| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Aug 29 2021 000 WTNT41 KNHC 290859 TCDAT1 Tropical Depression Eleven Discussion Number 2 NWS National Hurricane Center Miami FL AL112021 500 AM AST Sun Aug 29 2021 The depression continues to slowly organize this morning, with a distinct curved band stretching along the southeastern quadrant of the low-level circulation. However, the deep convection that was closer to the center earlier has recently been sheared off to the northeast due to increasing southwesterly vertical wind shear. The latest subjective Dvorak estimates from TAFB and SAB were T2.0/30 kt and T1.5/25 kt respectively. The latest objective ADT guidance was a bit higher at T2.4/34 kt. Taking a blend of these estimates, the intensity was held at 30 kt for this advisory, though the depression appears close to becoming a tropical storm. The depression is beginning to gradually accelerate, with the estimated motion now at 050/13 kt. A strong deep-layer trough will continue to steer the depression to the northeast in the short-term with increasing forward motion. After the system becomes a post-tropical cyclone, it is forecast to gradually pivot to the north and then northwest before dissipating in 72 hours. The latest NHC track forecast is a touch faster than the previous one, following the latest consensus track guidance. While vertical wind shear is expected to increase quite dramatically over the next 24-36 hours, strong baroclinic forcing should offset this negative factor and allow at least steady intensification in the short term especially as the cyclone accelerates. After 24 hours, the system will be crossing into much cooler sea-surface temperatures, and extratropical transition will likely be ongoing as the system merges with an advancing frontal boundary. The latest NHC intensity forecast follows the HCCA consensus aid closely, and is just a bit stronger in the short-term helped by the fast forward motion, with a peak intensity of 50-kt just before extratropical transition occurs. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 34.0N 48.6W 30 KT 35 MPH 12H 29/1800Z 35.8N 45.6W 40 KT 45 MPH 24H 30/0600Z 38.5N 41.3W 50 KT 60 MPH 36H 30/1800Z 41.8N 37.7W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 31/0600Z 45.9N 36.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 31/1800Z 50.0N 36.7W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 01/0600Z...DISSIPATED $$ Forecaster Papin
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Hurricane Ida Forecast Discussion Number 12
2021-08-29 10:59:59| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Sun Aug 29 2021 000 WTNT44 KNHC 290859 TCDAT4 Hurricane Ida Discussion Number 12 NWS National Hurricane Center Miami FL AL092021 400 AM CDT Sun Aug 29 2021 Ida has undergone some dramatic inner-core structural changes since the previous advisory. The eye between 25,000-45,000 ft has become circular with a diameter of about 15 nmi now, and at least two eyewall mesocyclones have been noted rotating cyclonically around the eyewall in both radar and high-resolution 1-minute GOES-16 satellite imagery. The result has been rapid strengthening of at least 30 kt during the past 6 hours, along with a pressure drop of more than 15 mb during that same time, with a 6-mb decrease having occurred in the 1-hr period between about 0500-0600 UTC based on Air Force Reserve reconnaissance aircraft eye dropsonde data. The aircraft also measured a maximum 700-mb flight-level wind speed of 133 kt in the northeastern quadrant, along with a peak SFMR surface wind speed of 116 kt. Furthermore, NWS Doppler radar velocity data from Slidell, Louisiana, has recently been measuring velocities of 120-130 kt between 25,000-30,000 ft, which is quite rare, and indicates that Ida is a vertically deep and intense hurricane. Ida was initialized with 115 kt at 0600 UTC, but the 0900 UTC advisory intensity has been increased to 120 kt based on the 133-kt flight-level wind and the improved structure in both radar data and satellite imagery since the 0609 UTC time of that aircraft observation. The initial motion remains northwestward, or 315/13 kt. There is no significant change to the previous forecast track or synoptic reasoning. The subtropical ridge oriented east-west along 30N-31N across the southeastern U.S. is forecast to remain intact through the forecast period with only minor shifts in the location and strength of the ridge. As a result, Ida should continue to move northwestward toward the southeastern Louisiana coast today, followed by a gradual turn toward the north tonight after landfall. On Monday, the hurricane is expected to move northeastward across the Tennessee Valley when Ida moves north of the ridge axis. Impacts and hazards will arrive well before the eye of the hurricane makes landfall. Tropical-storm-force winds are likely to begin later this morning. Therefore, all preparations to protect life and property must be rushed to completion. The new track forecast is basically just an update of the previous advisory track. Ida will remain over waters with high oceanic heat content for another 6 hours or so. Thereafter, the heat content will drop sharply to less than half of the current value of more than 100 units. However, some additional strengthening is expected until landfall occurs. After Ida moves inland tonight, rapid weakening is forecast due to a combination of land interaction, entrainment of drier air, and some increase in westerly vertical wind shear. 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. Rainfall impacts will also spread inland across the Lower Mississippi and Tennessee Valleys through early next week. Key Messages: 1. There is a danger of life-threatening storm surge inundation Sunday along the coasts of Louisiana, Mississippi, and Alabama within the Storm Surge Warning area. Extremely life-threatening inundation of 9 feet or greater above ground level is possible somewhere within the area from Morgan City, Louisiana, to the coast of Mississippi. Overtopping of local levees outside of the Hurricane and Storm Damage Risk Reduction System is possible where local inundation values may be higher. Interests throughout the warning area should follow any advice given by local officials. 2. Ida is expected to be an extremely dangerous major hurricane when it reaches the coast of southeastern 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. 3. Damaging winds, especially in gusts, will spread inland near the track of the center of Ida across portions of southeastern Louisiana and southwestern Mississippi Sunday night and early Monday. These winds will likely lead to widespread tree damage and power outages. 4. Ida will produce heavy rainfall today through Monday across the central Gulf Coast from southeastern Louisiana, coastal Mississippi, to far southwestern Alabama resulting in considerable to life-threatening flash and urban flooding and significant riverine flooding impacts. As Ida moves inland, significant flooding impacts are possible across portions of the Lower Mississippi, Tennessee, and Ohio Valleys through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 28.0N 89.1W 120 KT 140 MPH 12H 29/1800Z 29.1N 90.3W 125 KT 145 MPH...NEAR SERN LOUISIANA 24H 30/0600Z 30.6N 91.1W 70 KT 80 MPH...INLAND 36H 30/1800Z 32.2N 91.0W 45 KT 50 MPH...INLAND 48H 31/0600Z 33.8N 90.0W 30 KT 35 MPH...INLAND 60H 31/1800Z 35.4N 87.9W 25 KT 30 MPH...INLAND 72H 01/0600Z 36.7N 85.2W 20 KT 25 MPH...INLAND 96H 02/0600Z 38.9N 78.9W 20 KT 25 MPH...POST-TROP/INLAND 120H 03/0600Z...DISSIPATED $$ Forecaster Stewart
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Tropical Depression Ten Forecast Discussion Number 5
2021-08-29 10:56:29| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Aug 29 2021 034 WTNT45 KNHC 290856 TCDAT5 Tropical Depression Ten Discussion Number 5 NWS National Hurricane Center Miami FL AL102021 500 AM AST Sun Aug 29 2021 Tropical Depression Ten continues to struggle against 25-30 kt of northwesterly vertical wind shear, as diagnosed by the latest SHIPS guidance. Convection has thus remained displaced primarily to the southeast, though with some recent cells trying to develop closer to the center. The most recent TAFB and SAB Dvorak estimates were T2.5/35 kt and T2.0/30 kt with the objective ADT estimate at T2.3/33 kt. Given the disorganized nature of the current structure on IR satellite, I have elected to stay on the conservative side of these estimates and hold the intensity at 30 kt for this advisory. The depression continues to move toward the north at 360/9 kt. A large weakness in the mid-level ridging, due to a strong upper-tropospheric trough, will allow the depression to continue moving northward in the short-term, though there may be some occasional eastward bends as downshear convection tugs at the low-level vortex of the system. However by 72 h, some mid-level ridging is expected to build back in, allowing the track to shift a bit more leftward to the north-northwest after this point. The track guidance has not shifted much over the forecast period, and the latest NHC track forecast is nearly on top of the previous one, continuing to favor a blend of the the consensus aids (HCCA, TVCN). The poor current structure of the depression, under high shear importing dry air, argues against much short term intensification. However, the ECMWF-SHIPS guidance still suggests a brief respite in the shear between 12-24 hours. For this reason, the NHC intensity forecast still shows some slight strengthening to a tropical storm in 24 hours. Another round of 25-30 kt of vertical wind shear between 24-48 hours is then expected to keep the system in check, and it remains possible that the cyclone could degenerate to a remnant low over this time period. However, by 72 hours, the upper-level trough shearing the system is forecast to cut-off to the southwest, and this will shift the upper-level flow from northwesterly to southeasterly, which should provide a more favorable environment for strengthening. Thus, gradual strengthening is shown beginning in 72 hours extending through the end of the forecast. The latest NHC intensity forecast is quite similar to the previous forecast, favoring the more pessimistic ECMWF guidance versus the more aggressive GFS and regional hurricane models. There is quite a bit of uncertainty in the latter portion of this forecast since it is unclear how much of the cyclone will survive the current unfavorable environment during the next 2-3 days. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 17.3N 49.8W 30 KT 35 MPH 12H 29/1800Z 18.4N 49.8W 30 KT 35 MPH 24H 30/0600Z 19.9N 49.8W 35 KT 40 MPH 36H 30/1800Z 21.4N 49.4W 35 KT 40 MPH 48H 31/0600Z 22.7N 48.9W 35 KT 40 MPH 60H 31/1800Z 24.0N 48.9W 35 KT 40 MPH 72H 01/0600Z 25.6N 49.3W 40 KT 45 MPH 96H 02/0600Z 29.0N 50.5W 45 KT 50 MPH 120H 03/0600Z 32.0N 51.0W 50 KT 60 MPH $$ Forecaster Papin
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Hurricane Nora Forecast Discussion Number 15
2021-08-29 10:52:28| National Hurricane Center (East Pacific)
Issued at 400 AM CDT Sun Aug 29 2021 000 WTPZ44 KNHC 290852 TCDEP4 Hurricane Nora Discussion Number 15 NWS National Hurricane Center Miami FL EP142021 400 AM CDT Sun Aug 29 2021 There have been no recent in-situ observations for estimating the intensity of Nora, but the cyclone is still fairly well-organized on satellite images. Taking a blend of T- and Current Intensity numbers from TAFB and SAB along with ADT estimates from UW-CIMSS still supports keeping the system as a hurricane at this time. Center fixes indicate that Nora is moving a little west of due north at a decreased forward speed, or around 350/9 kt. The tropical cyclone is expected to move north-northwestward to northwestward during the next few days, on the southwestern side of a mid-level ridge. This would take Nora over the eastern part of the Gulf of California, but very near the coast of mainland Mexico over the next few days. The track guidance has shifted somewhat to the east, and now suggests that it is a very distinct possibility that the system will move inland much sooner than shown by the latest NHC track forecast. The future intensity of Nora is of course highly dependent on how soon the center moves inland. The official intensity forecast assumes that the system will remain just offshore so that only slow weakening will occur during the next 72 hours or so. This is in good agreement with the NOAA corrected consensus guidance. Alternatively, Nora may move inland sooner than indicated, in which case the system would probably dissipate in 2 to 3 days or less. Obviously, this intensity forecast is of low confidence. Key Messages: 1. Nora is forecast to be at or near hurricane strength while it moves near the coasts of Nayarit and Sinaloa through the weekend and into Monday, and hurricane warnings or watches 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 the west coast of Mexico from the states of Colima northward to southern Sonora. This rain will likely result in life-threatening flash flooding and mudslides across these regions. Rainfall from Nora is likely to spread into the southwestern U.S. and central Rockies during the middle to latter portion of the week, bringing the potential for flash flooding to the region. 3. Nora is forecast to move north-northwestward to northwestward over the Gulf of California Tuesday and Wednesday, bringing a risk of wind impacts to portions of the Mexican states of Baja California Sur, northern Sinaloa, and Sonora. Given the above-average uncertainty in the forecast intensity, confidence is not high enough to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 22.5N 105.9W 65 KT 75 MPH 12H 29/1800Z 23.6N 106.8W 65 KT 75 MPH 24H 30/0600Z 24.2N 107.4W 60 KT 70 MPH 36H 30/1800Z 24.7N 108.1W 60 KT 70 MPH 48H 31/0600Z 25.2N 108.8W 60 KT 70 MPH 60H 31/1800Z 26.0N 109.5W 55 KT 65 MPH 72H 01/0600Z 27.0N 110.2W 55 KT 65 MPH 96H 02/0600Z 29.5N 111.0W 30 KT 35 MPH...INLAND 120H 03/0600Z...DISSIPATED $$ Forecaster Pasch
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Hurricane Nora Forecast Discussion Number 14
2021-08-29 04:59:24| National Hurricane Center (East Pacific)
Issued at 1000 PM CDT Sat Aug 28 2021 000 WTPZ44 KNHC 290259 TCDEP4 Hurricane Nora Discussion Number 14 NWS National Hurricane Center Miami FL EP142021 1000 PM CDT Sat Aug 28 2021 Surface data from Mexico, data from an Air Force Reserve Hurricane Hunter aircraft, and microwave imagery from an 2344 UTC SSMIS indicate that the center of Nora moved over the far northwestern coast of Jalisco earlier this evening. Since then, the cloud pattern of the hurricane has degraded, but not enough to bring the latest Dvorak estimates below hurricane strength. The advisory intensity is therefore set at 65 kt based on the assumption that interaction with land has caused weakening, however there is low confidence in this assessment. The ever-so-slight rightward deviation from the forecast track that brought Nora inland, at least briefly, highlights the sensitivity of the system's future to its exact track. A sizable portion of the latest dynamical guidance, including the GFS, ECMWF, and HWRF models indicate that Nora will move inland tonight or early Sunday and dissipate. All three models also indicate it could reform over the Gulf of California in a few days. Other models, like the UKMET and CMC global models maintain Nora as a coherent tropical cyclone much longer. While the models can easily flip flop from run to run, the NHC forecast cannot drastically change solutions so cavalierly. Therefore, the official forecast is based on the condition that Nora will stay far enough offshore to persist as a tropical cyclone. Regardless of its exact state, Nora is forecast to turn toward the northwest on Sunday and then move along the coast toward northern Mexico early next week. This general solution is supported by all of the available guidance. A slight eastward adjustment has been made to the NHC track forecast to account for the slightly east initial position. Given Nora's recent movement over land, the intensity forecast has been lowered substantially at all forecast hours, but still maintains Nora near hurricane strength for the next couple of days. This is well above the most recent intensity consensus, which is heavily influenced by the dynamical models that move Nora inland. If it doesn't move inland sooner, Nora will likely quickly weaken as it moves permanently inland by around 96 h, and become a remnant low by the end of the forecast period. Key Messages: 1. Nora is forecast to be at or near hurricane strength while it moves near the coasts of Nayarit and Sinaloa through the weekend, and hurricane 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 the west coast of Mexico from the states of Michoacan northward to southern Sonora, including Baja California Sur. This rain will likely result in life-threatening flash flooding and mudslides across these regions. Rainfall from Nora may spread into the southwestern U.S. and central Rockies during the middle to latter portion of next week. 3. Nora is forecast to continue moving northward over the Gulf of California Tuesday and Wednesday, bringing a risk of wind impacts to portions of the Mexican states of Baja California Sur, northern Sinaloa, and Sonora. Given the above-average uncertainty in the forecast intensity, confidence is not high enough to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 21.3N 105.5W 65 KT 75 MPH 12H 29/1200Z 22.8N 106.2W 65 KT 75 MPH 24H 30/0000Z 23.7N 107.1W 60 KT 70 MPH 36H 30/1200Z 24.4N 107.9W 60 KT 70 MPH 48H 31/0000Z 24.9N 108.6W 60 KT 70 MPH 60H 31/1200Z 25.6N 109.4W 55 KT 65 MPH 72H 01/0000Z 26.8N 110.1W 55 KT 65 MPH 96H 02/0000Z 28.6N 110.7W 35 KT 40 MPH...INLAND 120H 03/0000Z 30.2N 110.9W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster D. Zelinsky
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