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Hurricane Ida Forecast Discussion Number 14
2021-08-29 16:56:33| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Sun Aug 29 2021 167 WTNT44 KNHC 291456 TCDAT4 Hurricane Ida Discussion Number 14 NWS National Hurricane Center Miami FL AL092021 1000 AM CDT Sun Aug 29 2021 Ida's rapid strengthening appears to have leveled off within the past hour or so. NOAA and Air Force Reserve Hurricane Hunter aircraft that have been in the storm this morning have reported peak flight-level winds of 146 to 148 kt between 8000 and 10000 ft, and believable SFMR winds around 130 kt. Based on these observations, the initial wind speed remains 130 kt for this advisory. The central pressure appears to have bottomed out around 929 mb, and the latest dropsonde in the eye from the Air Force plane supports a minimum pressure of 933 mb. Ida's satellite and radar presentation is very impressive, as the 15-nm-wide eye is very well-defined and surrounded by a ring of intense convection. Within the past hour or so, there is evidence in radar imagery of a secondary eyewall, and this has likely caused Ida's intensity to level off for now. Although Ida's extreme winds are confined to the inner eyewall, the aircraft data indicate that hurricane-force winds extend outward about 45 n mi to the northeast of the center, and based on buoy data the tropical-storm-force wind field extends outward about 130 n mi northeast of the center. Ida's eyewall is nearing the coast of Louisiana, and any additional strengthening seems less likely now given the recent structural changes of the inner core. While rapid weakening should occur after landfall, damaging winds will penetrate well inland across southeastern Louisiana and southwestern Mississippi through tonight. Ida is forecast to weaken to a tropical depression over Mississippi by late Tuesday. The global model guidance now indicates that Ida will likely transition to an extratropical low when it nears the east coast of the United States and the new forecast shows the extratropical low becoming a gale center near Atlantic Canada at day 5. Ida has begun to slow down according to the latest aircraft and radar fixes, and the initial motion estimate is 320/11 kt. Ida's forward speed is likely to slow further during the next 12 to 24 hours as the hurricane turns north-northwestward, and then northward around the western periphery of a deep-layer ridge near the southeastern United States coast. The cyclone is predicted to turn northeastward by late Tuesday ahead of a short-wave trough that will move across the central United States. The new NHC track is close to the HCCA corrected consensus and the GFS ensemble mean, and is not very different from the previous advisory. Key Messages: 1. Extremely life-threatening storm surge inundation of 9 feet or greater above ground level is imminent somewhere within the area from 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. Catastrophic wind damage will occur where the core of Ida moves onshore along the southeast coast of Louisiana in the next few hours. Hurricane-force winds and damaging wind gusts are expected today within the Hurricane Warning in southeastern Louisiana, including metropolitan New Orleans. 3. Damaging winds, especially in gusts, will spread inland near the track of the center of Ida into southwestern Mississippi tonight and early Monday. These winds will likely lead to widespread tree damage and power outages. 4. Ida will continue to produce heavy rainfall today through Monday across the central Gulf Coast from southeast Louisiana, coastal Mississippi, and far southwestern Alabama, resulting in considerable to life-threatening flash and urban flooding and significant river flooding impacts. As Ida moves inland, significant flooding impacts are possible across portions of the Lower Mississippi, Tennessee Valley, Upper Ohio Valley, Central Appalachians and the Mid-Atlantic through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 28.8N 90.0W 130 KT 150 MPH 12H 30/0000Z 30.0N 90.8W 90 KT 105 MPH...INLAND 24H 30/1200Z 31.6N 91.0W 50 KT 60 MPH...INLAND 36H 31/0000Z 33.2N 90.3W 30 KT 35 MPH...INLAND 48H 31/1200Z 34.9N 88.5W 25 KT 30 MPH...INLAND 60H 01/0000Z 36.4N 85.9W 20 KT 25 MPH...INLAND 72H 01/1200Z 37.8N 82.5W 20 KT 25 MPH...POST-TROP/INLAND 96H 02/1200Z 40.5N 74.2W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 03/1200Z 43.5N 67.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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Tropical Storm Julian Forecast Discussion Number 3
2021-08-29 16:53:37| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Aug 29 2021 000 WTNT41 KNHC 291453 TCDAT1 Tropical Storm Julian Discussion Number 3 NWS National Hurricane Center Miami FL AL112021 1100 AM AST Sun Aug 29 2021 The system has become better organized this morning, with the low-level center located on the southwestern edge of a persistent mass of deep convection. A 1246 UTC ASCAT-B pass revealed an area of winds over 40 kt southeast of the center, so the system is upgraded to Tropical Storm Julian with maximum winds of 45 kt. Julian is accelerating toward the northeast (045/15 kt) in the flow to the south of a deep-layer area of low pressure located just east of Newfoundland. The storm is expected to move around the southeastern and eastern periphery of this large low during the next few days, accelerating further and turning toward the north by 48 hours. The track models are all in good agreement on this scenario, and the NHC track forecast is very close to the TVCA and HCCA consensus aids. This new forecast is also relatively unchanged from the previous advisory. Winds in the storm have increased faster than expected, even in the face of 20 kt of west-southwesterly shear. This shear is forecast to increase substantially in the coming days, with SHIPS diagnostics indicating it may reach magnitudes of 40-50 kt. However, the storm will still be moving over marginally warm waters around 26 degrees Celsius, and its fast motion and some baroclinic forcing could allow for additional strengthening during the next 12-24 hours. Nearly all the intensity models support some strengthening, and the NHC official forecast peaks the winds at 55 kt in 24 hours, roughly between the IVCN and HCCA solutions. Phase-space diagrams suggest that Julian will probably already be going through extratropical transition at that time, and it should be fully extratropical by 36 hours. Gradual weakening is anticipated after 24 hours, and the extratropical low is likely to dissipate over the north Atlantic by day 3. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 35.1N 46.8W 45 KT 50 MPH 12H 30/0000Z 36.9N 43.7W 50 KT 60 MPH 24H 30/1200Z 40.0N 39.7W 55 KT 65 MPH 36H 31/0000Z 43.6N 37.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 31/1200Z 48.0N 36.8W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 01/0000Z 52.2N 38.2W 40 KT 45 MPH...POST-TROP/EXTRATROP 72H 01/1200Z...DISSIPATED $$ Forecaster Berg
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Hurricane Nora Forecast Discussion Number 16
2021-08-29 16:46:04| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Sun Aug 29 2021 000 WTPZ44 KNHC 291445 TCDEP4 Hurricane Nora Discussion Number 16 NWS National Hurricane Center Miami FL EP142021 900 AM MDT Sun Aug 29 2021 Nora has a healthy satellite appearance this morning. The deep convection near and to the west of the estimated center is maintaining a fairly large central dense overcast with very cold infrared cloud tops. Recent ATMS and SSMIS microwave data indicate Nora still has a pronounced mid-level eye structure, with the center very near the coast of extreme southern Sinaloa. A blend of the UW-CIMSS objective ADT estimate and 12 UTC subjective Dvorak classifications from TAFB and SAB support holding the initial intensity at 65 kt for this advisory. The estimated initial motion of Nora is north-northwestward or 345/9 kt, although this is somewhat uncertain due to the lack of in-situ observations. A mid-level ridge should continue to steer the tropical cyclone generally north-northwestward to northwestward during the next few days. This motion will bring the center over the eastern Gulf of California and very near or over the coast of west-central Mexico. The official NHC track forecast is adjusted just slightly to the right of the previous one, in line with the latest track guidance. Nora's intensity forecast remains highly dependent on whether the center moves inland over mainland Mexico or along the Gulf of California, parallel to the west-central coast of Mexico. Given the slight eastward track adjustment, the official NHC intensity forecast shows gradual weakening over the next few days due to at least intermittent land interaction as Nora skirts the coast. This is consistent with the general intensity guidance consensus, which no longer supports strengthening given Nora's proximity to land. Due to the complex geography of western Mexico, even a slight eastward deviation from the forecast track would result in more rapid weakening as Nora moves further inland. Conversely, a more northwestward motion over the warm Gulf of California waters could allow Nora to remain a stronger tropical storm early this week. As previously mentioned, confidence in the intensity forecast is lower than normal. Key Messages: 1. Nora is forecast to be at or near hurricane strength while it moves near the coasts of Nayarit and Sinaloa today 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 near or 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 intensity forecast, confidence is not high enough to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 23.3N 106.4W 65 KT 75 MPH 12H 30/0000Z 23.8N 106.9W 60 KT 70 MPH...NEAR THE COAST 24H 30/1200Z 24.3N 107.5W 55 KT 65 MPH...NEAR THE COAST 36H 31/0000Z 24.9N 108.2W 55 KT 65 MPH...NEAR THE COAST 48H 31/1200Z 25.6N 109.0W 50 KT 60 MPH...NEAR THE COAST 60H 01/0000Z 26.5N 109.6W 50 KT 60 MPH...NEAR THE COAST 72H 01/1200Z 27.5N 110.0W 40 KT 45 MPH...INLAND 96H 02/1200Z 29.5N 111.2W 30 KT 35 MPH...INLAND 120H 03/1200Z...DISSIPATED $$ Forecaster Reinhart
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Tropical Depression Ten Forecast Discussion Number 6
2021-08-29 16:33:33| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Aug 29 2021 775 WTNT45 KNHC 291433 TCDAT5 Tropical Depression Ten Discussion Number 6 NWS National Hurricane Center Miami FL AL102021 1100 AM AST Sun Aug 29 2021 The center of the depression has become a little more exposed to the northwest of the deep convection during the past few hours as a result of continued 25-30 kt of northwesterly shear. The latest Dvorak estimates are T2.5 from TAFB and T1.0/2.0 from SAB, so the initial intensity remains 30 kt. The system is expected to continue moving through a region of strong northwesterly to westerly shear for the next 2 days or so, and little to no strengthening is anticipated during that time. However, if the convection is able to remain fairly close to the center, then the system could eke into tropical storm status at any time. After 48 hours, a significant decrease in shear, along with warm waters of 27-28 degrees Celsius, should allow for a steady strengthening trend. The NHC intensity forecast has been nudged upward on days 3 through 5, although much of the guidance is even higher, suggesting that further adjustments could be required in subsequent advisories. The depression is moving northward (350/10 kt) through a break in the ridge created by a large deep-layer trough extending south of Newfoundland over the central Atlantic. This trough, along with a strengthening mid-level ridge over the eastern Atlantic on days 3-5, are expected to keep the cyclone on a curvy northward track during the entire forecast period. There is high confidence in the track forecast given low spread among the track models, and the NHC official forecast generally lies between the TVCA and HCCA consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 18.8N 50.2W 30 KT 35 MPH 12H 30/0000Z 20.0N 50.3W 30 KT 35 MPH 24H 30/1200Z 21.4N 50.1W 35 KT 40 MPH 36H 31/0000Z 22.7N 49.5W 35 KT 40 MPH 48H 31/1200Z 24.1N 49.1W 35 KT 40 MPH 60H 01/0000Z 25.6N 49.2W 40 KT 45 MPH 72H 01/1200Z 27.4N 49.8W 45 KT 50 MPH 96H 02/1200Z 30.6N 50.6W 50 KT 60 MPH 120H 03/1200Z 33.5N 50.7W 55 KT 65 MPH $$ Forecaster Berg
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Hurricane Ida Forecast Discussion Number 13
2021-08-29 13:58:33| National Hurricane Center (Atlantic)
Issued at 700 AM CDT Sun Aug 29 2021 000 WTNT44 KNHC 291158 TCDAT4 Hurricane Ida Special Discussion Number 13 NWS National Hurricane Center Miami FL AL092021 700 AM CDT Sun Aug 29 2021 Recent reports from both NOAA and Air Force Reserve Hurricane Hunter aircraft indicate that Ida has continued to strengthen since the 0900 UTC advisory and the maximum winds are estimated to be 130 kt. This intensity is based on peak 700-mb flight-level winds of 146 kt that have been reported by both aircraft and believable SFMR winds of around 130 kt. The NOAA aircraft very recently reported that the minimum pressure has fallen to around 933 mb. This special advisory is issued to raise the 12-hour forecast intensity to 135 kt, but it is possible that Ida could peak slightly above that before landfall occurs. The initial motion estimate is 320/13 kt, slightly faster than the previous forecast. Therefore, the 12-hour forecast point has also been adjusted slightly. No other changes were made to the track or intensity forecasts. The initial and forecast 64-kt wind radii were adjusted outward in the northeast and southeast quadrants based on aircraft data. Note that this Special advisory replaces the regular 1200 UTC (700 AM CDT) intermediate public advisory. Key Messages: 1. Extremely life-threatening storm surge inundation of 9 feet or greater above ground level is imminent somewhere within the area from 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. Interests throughout the Storm Surge Warning area should follow any advice given by local officials. 2. Catastrophic wind damage is likely where the core of Ida moves onshore along the southeast coast of Louisiana in the next few hours. Hurricane-force winds are expected today within the Hurricane Warning area along the Louisiana coast, including metropolitan New Orleans. 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 today through 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 river 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 29/1200Z 28.5N 89.6W 130 KT 150 MPH 12H 29/1800Z 29.2N 90.4W 135 KT 155 MPH 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 Brown/Brennan
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