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Tropical Depression Ten Forecast Discussion Number 9
2021-08-30 10:58:23| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Aug 30 2021 000 WTNT45 KNHC 300858 TCDAT5 Tropical Depression Ten Discussion Number 9 NWS National Hurricane Center Miami FL AL102021 500 AM AST Mon Aug 30 2021 The deep convection with Tropical Depression Ten is in a sheared bursting pattern this morning, associated with overshooting cloud top temperatures below -80 C. A 0518 UTC AMSR-2 microwave pass did show a bit of banding associated with this activity on the 37 GHz low-level channel. However, Proxy-Vis satellite imagery indicates this convective activity remains located downshear of the low-level center thanks to very strong 30-50 kt northwesterly flow associated with a subtropical jet at 200 mb. The latest round of subjective Dvorak estimates were 25 kt from SAB and 35 kt from TAFB. Taking a blend of these estimates and the earlier ASCAT wind data supports keeping the intensity at 30 kt for this advisory. The depression has resumed a northward motion this morning, with the latest estimate at 360 degrees at 7 kt. A deep-layer trough passing by well to the north is continuing to provide a weakness in the subtropical ridge, allowing the cyclone to escape northward. The system could even move a bit east of due north over the next 24-36 hours if down-shear convective bursts help to drag the low-level center a bit right of the steering flow. After 36 hours, the deep-layer trough moves eastward, allowing the subtropical ridge to build back in. The net result is that the depression should turn leftward and begin a more northwestward motion by the latter part of this week. The latest track guidance has once again made another westward shift this cycle after 36 hours, and the NHC track forecast has been nudged in that direction as well. However, the latest track is still not as far west as the GFS & ECMWF models, and further westward adjustments may be needed in subsequent forecasts. Strong upper-level flow is the primary hindrance for the depression currently. In fact, both GFS & ECMWF-based SHIPS guidance shows the vertical wind shear remaining above 30 kt for the next 24 hours as the cyclone moves through the core of a subtropical jet streak. Interestingly, this shearing flow seems to be mostly based in the upper-levels, with much lower mid-level shear diagnosed by UW-CIMSS. This lower mid-level shear may help explain why deep-convection has not yet been completely stripped away from the low-level center. After 36 hours, most of the guidance agrees that an upper-level low will cut off to the southwest of the depression, providing a more favorable upper-level environment over the system. However, it remains unclear what will be left of the depression by that time, and the latest 00z ECMWF, HWRF, and HMON runs suggest the vortex will be too weak and diffuse to take advantage of the more favorable conditions. For now, the latest NHC intensity forecast will maintain the current intensity through 48 hours, with only modest intensification beginning after that time assuming the circulation is coherent enough to take advantage of the more favorable environment. The latest intensity forecast is just a bit lower than the previous forecast, and is also lower than the HCCA and IVCN consensus aids. It remains distinctly possible that the depression could become a remnant low if its convection is completely stripped away. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 20.8N 50.6W 30 KT 35 MPH 12H 30/1800Z 21.7N 50.6W 30 KT 35 MPH 24H 31/0600Z 22.6N 50.3W 30 KT 35 MPH 36H 31/1800Z 23.6N 50.1W 30 KT 35 MPH 48H 01/0600Z 24.8N 50.7W 30 KT 35 MPH 60H 01/1800Z 26.1N 51.7W 35 KT 40 MPH 72H 02/0600Z 27.6N 53.1W 40 KT 45 MPH 96H 03/0600Z 30.8N 55.3W 45 KT 50 MPH 120H 04/0600Z 35.1N 53.6W 50 KT 60 MPH $$ Forecaster Papin
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Remnants of Nora Forecast Discussion Number 19
2021-08-30 10:53:00| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Mon Aug 30 2021 000 WTPZ44 KNHC 300852 TCDEP4 Remnants Of Nora Discussion Number 19 NWS National Hurricane Center Miami FL EP142021 300 AM MDT Mon Aug 30 2021 Satellite analysts have been unable to identify a low-level center associated with Nora, and scatterometer and synoptic data show no surface circulation. Therefore the system has dissipated and this is the last advisory on this system. However, the moisture field of Nora's remnants will continue to move poleward over the next few days and could contribute to rainfall enhancement over the southwestern United States later this week. Key Messages: 1. Heavy rain associated with Nora's remnants is expected across the states of Sinaloa and Sonora. This rain will likely result in life-threatening flash flooding and mudslides. Rainfall from the remnants of Nora is also likely to spread into the southwestern U.S. and central Rockies beginning Wednesday, bringing the potential for flash flooding to the region. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 25.3N 108.1W 25 KT 30 MPH 12H 30/1800Z...DISSIPATED $$ Forecaster Pasch
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Post-Tropical Cyclone Julian Forecast Discussion Number 5
2021-08-30 04:46:14| National Hurricane Center (Atlantic)
Issued at 300 AM GMT Mon Aug 30 2021 380 WTNT41 KNHC 300246 TCDAT1 Post-Tropical Cyclone Julian Discussion Number 5 NWS National Hurricane Center Miami FL AL112021 300 AM GMT Mon Aug 30 2021 Julian has been showing signs of a transition into an extratropical cyclone over the past several hours. The deep convection has become detached to the northeast from the low-level center and cloud tops of that convection are warming. A line of convection to the south of the center resembles a frontal boundary, with recent scatterometer data showing a notable wind shift along that line. Based on the structural changes noted above, as well as a majority of FSU phase-space diagrams from the various global models, Julian is estimated to have transitioned to an extratropical cyclone. Recent ASCAT data showed the cyclone's intensity remains 50 kt. The cyclone is forecast to maintain this intensity through Monday before weakening. It is then forecast to dissipate in a few days over the northern Atlantic. The system should continue to move quickly northeastward through Monday, then turn northward and northwestward Monday night into Tuesday. This is the last advisory on Julian by the National Hurricane Center. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 38.1N 41.9W 50 KT 60 MPH...POST-TROPICAL 12H 30/1200Z 40.3N 39.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 31/0000Z 44.1N 36.4W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 31/1200Z 48.5N 36.2W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 01/0000Z 53.0N 38.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 60H 01/1200Z 57.0N 40.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 02/0000Z...DISSIPATED $$ Forecaster Latto
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Hurricane Ida Forecast Discussion Number 16
2021-08-30 04:44:45| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Sun Aug 29 2021 000 WTNT44 KNHC 300244 TCDAT4 Hurricane Ida Discussion Number 16 NWS National Hurricane Center Miami FL AL092021 1000 PM CDT Sun Aug 29 2021 Although Ida has been inland over southeastern Louisiana for several hours, it is still a very well organized hurricane. Doppler radar images indicate that the hurricane continues to have a well-defined eye, though the eyewall has become a bit ragged on the southwest side. Beyond the inner core, rain bands remain well established, especially on the system's east side. Earlier this evening, there were reports of extreme wind gusts over 120 kt along the coast of southeastern Louisiana. Based on Doppler radar velocity data over the past hour or two, the initial intensity is estimated to be 90 kt. As Ida continues inland, rapid weakening is expected due to a combination of land interaction and an increase in wind shear. However, damaging winds, especially in gusts, are expected to spread further inland over southeastern Louisiana and southwestern Mississippi through Monday morning. To account for this, the gust factor in the Forecast/Advisory has been adjusted accordingly. Ida is likely to weaken to a tropical storm by Monday morning and a tropical depression by Monday night. Some slight restrengthening as an extratropical storm is possible when Ida moves over the western Atlantic in 4 days or so. In addition, heavy rains will spread northward and then northeastward along the forecast track. Ida is expected to turn northward by early Monday as it moves in the flow on the western side of a subtropical ridge. A faster motion to the northeast is expected by Tuesday as a mid- to upper-level trough approaches the system, with that motion continuing through much of the remainder of the week. The NHC track forecast is a little to the south or right of the previous one to come into better agreement with the latest models. Key Messages: 1. Life-threatening storm surge inundation will continue through tonight along portions of the coast between Burns Point, Louisiana, to Ocean Springs, 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. Wind damage will occur near the core of Ida as it continues inland over southeastern Louisiana during the next few hours. Damaging winds, especially in gusts, will spread inland near the track of Ida's center into southwestern Mississippi through early Monday. These winds will likely lead to widespread tree damage and power outages. 3. Ida will continue to produce heavy rainfall tonight through Monday across 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 farther inland, considerable flooding impacts are possible across portions of the Lower Mississippi Valley, Tennessee Valley, Upper Ohio Valley, Central Appalachians, and Mid-Atlantic through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 30.3N 90.7W 90 KT 105 MPH...INLAND 12H 30/1200Z 31.5N 90.8W 50 KT 60 MPH...INLAND 24H 31/0000Z 33.0N 90.1W 30 KT 35 MPH...INLAND 36H 31/1200Z 34.6N 88.5W 25 KT 30 MPH...INLAND 48H 01/0000Z 36.1N 85.9W 25 KT 30 MPH...POST-TROP/INLAND 60H 01/1200Z 37.5N 82.5W 25 KT 30 MPH...POST-TROP/INLAND 72H 02/0000Z 38.9N 78.8W 30 KT 35 MPH...POST-TROP/EXTRATROP 96H 03/0000Z 40.0N 72.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 120H 04/0000Z 40.7N 67.9W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi
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Tropical Storm Nora Forecast Discussion Number 18
2021-08-30 04:41:42| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Sun Aug 29 2021 168 WTPZ44 KNHC 300241 TCDEP4 Tropical Storm Nora Discussion Number 18 NWS National Hurricane Center Miami FL EP142021 900 PM MDT Sun Aug 29 2021 Nora appears to have moved inland, and it is unclear if it still has a well-defined surface center. Earlier microwave data was inconclusive regarding the existence of the low level center, while the Dvorak analysts from TAFB and SAB were each unable to fix Nora's center over water. The intensity has been lowered to 35 kt, assuming weakening has occurred due to continued interaction with land. Baring an unexpected redevelopment of the center over water, Nora should continue to weaken inland, and could dissipate as soon as early Monday. Quick dissipation is now supported by all of the dynamical guidance. Accordingly, the NHC intensity forecast has been adjusted much lower than in the previous advisory. Nora is forecast to become post-tropical tomorrow and dissipate by Tuesday. Based on recent trends, this forecast is probably generous. Despite the uncertainty associated with Nora's position, the system still appears to be moving generally north-northwestward, with an initial motion of 330/10 kt. None of the dynamical guidance is able to track a low-level center more than about 24 h. However,there is good agreement that the mid-level remnants of Nora will continue moving generally northwestward and could contribute to heavy rain across northwest Mexico and portions of the southwestern U.S. during the middle to latter portion of the week. Key Messages: 1. Heavy rain associated with Nora is expected across the west coast of Mexico from the states of Nayarit 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 FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 24.8N 107.9W 35 KT 40 MPH 12H 30/1200Z 25.4N 108.4W 35 KT 40 MPH...INLAND 24H 31/0000Z 26.3N 109.1W 30 KT 35 MPH...POST-TROP/INLAND 36H 31/1200Z 27.0N 109.6W 25 KT 30 MPH...POST-TROP/INLAND 48H 01/0000Z...DISSIPATED $$ Forecaster D. Zelinsky
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