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Tropical Storm Ida Forecast Discussion Number 3

2021-08-27 05:23:39| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Thu Aug 26 2021 000 WTNT44 KNHC 270322 CCA TCDAT4 Tropical Storm Ida Discussion Number 3...Corrected NWS National Hurricane Center Miami FL AL092021 1100 PM EDT Thu Aug 26 2021 Corrected Key Message Number 4 The Air Force Hurricane Hunters have been investigating Ida this evening and found maximum flight-level winds of 47 kt at 2500 ft. This data along with numerous unflagged 35-kt SFMR winds supported raising the intensity to 35 kt earlier this evening. Since the aircraft departed Ida, there has been little change in the storm's structure, so the initial intensity was held at 35 kt. Ida is an asymmetric tropical storm with most of the deep convection and stronger winds confined to the eastern half of the circulation. Both the NOAA and Air Force Hurricane Hunters will be investigating Ida Friday morning. The storm has been wobbling around, but smoothing through the recent erratic motion yields an initial motion estimate of 320/10 kt. A mid-level ridge centered off the southeast U.S. coast is expected to shift westward on Friday and over the weekend. This feature should keep Ida moving on a general northwestward track for the next 2 or 3 days, taking the core of the system over western Cuba Friday afternoon or evening and then across the southern and central Gulf of Mexico this weekend. Although some model timing differences remain, they are in fairly good agreement that Ida will make landfall in Louisiana late Sunday or early Monday. The GFS and ECMWF ensemble members basically span a similar region and are most concentrated across the state of Louisiana. Users are reminded to not focus on the exact forecast track as impacts will extend far from the center and the average 72-hour track error is around 120 miles. There is some southwesterly vertical wind shear affecting Ida at the moment, which is the likely part of the reason the cloud pattern and wind field are asymmetric. However, the global model show the upper-level pattern becoming quite favorable late Friday and through the weekend. These more conducive winds aloft combined with very warm SSTs and abundant moisture is likely to result in steady or rapid intensification until Ida makes landfall in the U.S. The intensity guidance unanimously show Ida becoming a hurricane, but there is notable spread in how strong the system will become. Given the expected favorable environmental conditions for the storm, the NHC intensity forecast lies near the high end of the model guidance, in best agreement with the regional hurricane models. It is also worth noting that even though the global models are not particularly accurate in predicting tropical cyclone winds, the GFS and ECMWF show the minimum pressure falling more than 35 mb from the current conditions. Based on all of this information, there is higher-than-normal confidence that a significant hurricane will be approaching the Gulf coast late this weekend. Key Messages: 1. Tropical storm conditions are expected in portions of the Cayman Islands tonight and in portions of western Cuba and the Isle of Youth Friday, where a dangerous storm surge is also possible in areas of onshore flow. 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 an increasing risk of life-threatening storm surge inundation along the coasts of Louisiana, Mississippi, and Alabama, where a Storm Surge Watch is in effect. Interests in these areas should follow any advice given by local officials. 3. There is an increasing risk of dangerous hurricane-force winds beginning Sunday along the portions of the coasts of Louisiana and Mississippi, including metropolitan New Orleans, where a Hurricane Watch is in effect. 4. Ida is likely to produce heavy rainfall Sunday into Monday along the central Gulf coast resulting in flash, urban, small stream, and riverine flooding. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 18.6N 80.5W 35 KT 40 MPH 12H 27/1200Z 19.9N 82.0W 45 KT 50 MPH 24H 28/0000Z 21.8N 83.9W 55 KT 65 MPH...NEAR CUBA 36H 28/1200Z 23.8N 85.9W 65 KT 75 MPH 48H 29/0000Z 25.6N 88.0W 75 KT 85 MPH 60H 29/1200Z 27.3N 89.6W 85 KT 100 MPH 72H 30/0000Z 29.0N 90.6W 95 KT 110 MPH...NEAR THE COAST 96H 31/0000Z 32.0N 91.0W 45 KT 50 MPH...INLAND 120H 01/0000Z 33.9N 88.8W 25 KT 30 MPH...INLAND $$ Forecaster Cangialosi

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Tropical Storm Ida Forecast Discussion Number 3

2021-08-27 04:51:11| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Thu Aug 26 2021 000 WTNT44 KNHC 270251 TCDAT4 Tropical Storm Ida Discussion Number 3 NWS National Hurricane Center Miami FL AL092021 1100 PM EDT Thu Aug 26 2021 The Air Force Hurricane Hunters have been investigating Ida this evening and found maximum flight-level winds of 47 kt at 2500 ft. This data along with numerous unflagged 35-kt SFMR winds supported raising the intensity to 35 kt earlier this evening. Since the aircraft departed Ida, there has been generally little change in the storm's structure, so the initial intensity is held at 35 kt. Ida is an asymmetric tropical storm with most of the deep convection and stronger winds confined to the eastern half of the circulation. Both the NOAA and Air Force Hurricane Hunters will be investigating Ida Friday morning. The storm has been wobbling around, but smoothing through the recent erratic motion yields an initial motion estimate of 320/10 kt. A mid-level ridge centered off the southeast U.S. coast is expected to shift westward on Friday and over the weekend. This feature should keep Ida moving in a general northwestward motion for the next 2 or 3 days, taking the core of the system over western Cuba Friday afternoon or evening and then across the southern and central Gulf of Mexico this weekend. Although there is some timing differences in the models, they are in fairly good agreement that Ida will make landfall in Louisiana late Sunday or early Monday. The GFS and ECMWF ensemble members basically span a similar region and are most concentrated across the state of Louisiana. Users are reminded to not focus on the exact forecast track as impacts will extend far from the center and the average 72-hour track error is around 120 miles. There is some southwesterly vertical wind shear affecting Ida at the moment, which is the likely part of the reason the cloud pattern and wind field are asymmetric. However, the global model show the upper-level pattern becoming quite favorable late Friday and through the weekend. These more conducive winds aloft combined with very warm SSTs and abundant moisture is likely to result in steady or rapid intensification until Ida makes landfall in the U.S. The intensity guidance unanimously show Ida becoming a hurricane, but there is notable spread in how strong the system will become. Given the expected favorable environmental conditions for the storm, the NHC intensity forecast lies near the high end of the model guidance, in best agreement with the regional hurricane models. It is also worth noting that even though the global models are not particularly accurate in predicting tropical cyclone winds, the GFS and ECMWF show the minimum pressure falling more than 35 mb from the current conditions. Based on all of this information, there is higher-than-normal confidence that a significant hurricane will be approaching the Gulf coast late in the weekend. Key Messages: 1. Tropical storm conditions are expected in portions of the Cayman Islands tonight and in portions of western Cuba and the Isle of Youth Friday, where a dangerous storm surge is also possible in areas of onshore flow. 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 an increasing risk of life-threatening storm surge inundation along the coasts of Louisiana, Mississippi, and Alabama, where a Storm Surge Watch is in effect. Interests in these areas should follow any advice given by local officials. 3. There is an increasing risk of dangerous hurricane-force winds beginning Sunday along the portions of the coasts of Louisiana and Mississippi, including metropolitan New Orleans, where a Hurricane Watch is in effect. 4. Ida is likely to produce heavy rainfall Sunday into Monday along the central Gulf coast resulting in flash, urban, small stream, and riverine flooding. Heavy rainfall and flooding impacts are likely along the central Gulf Coast Sunday into Monday. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 18.6N 80.5W 35 KT 40 MPH 12H 27/1200Z 19.9N 82.0W 45 KT 50 MPH 24H 28/0000Z 21.8N 83.9W 55 KT 65 MPH...NEAR CUBA 36H 28/1200Z 23.8N 85.9W 65 KT 75 MPH 48H 29/0000Z 25.6N 88.0W 75 KT 85 MPH 60H 29/1200Z 27.3N 89.6W 85 KT 100 MPH 72H 30/0000Z 29.0N 90.6W 95 KT 110 MPH...NEAR THE COAST 96H 31/0000Z 32.0N 91.0W 45 KT 50 MPH...INLAND 120H 01/0000Z 33.9N 88.8W 25 KT 30 MPH...INLAND $$ Forecaster Cangialosi

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Tropical Storm Nora Forecast Discussion Number 6

2021-08-27 04:51:11| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Thu Aug 26 2021 000 WTPZ44 KNHC 270251 TCDEP4 Tropical Storm Nora Discussion Number 6 NWS National Hurricane Center Miami FL EP142021 1000 PM CDT Thu Aug 26 2021 A large area of deep convection has developed over the southern and western portions of Nora's circulation over the past several hours. Almost all of the convection is displaced to the southwest of Nora's center by some moderate northeasterly shear. Based on the slightly improved satellite appearance of the cyclone, the initial intensity is raised to 40 kt for this advisory. This is in best agreement with the objective UW-CIMSS ADT and SATCON estimates of around 40 kt. Nora has turned a bit to the right and accelerated slightly this evening, and it is now moving west-northwestward or 295/10 kt. The mid-level ridge over the southern United States that is steering Nora is being eroded by a shortwave trough over the Rocky Mountains. In response, Nora is expected to turn toward the northwest on Friday and then the north-northwest on Saturday. This will bring the center of the cyclone close to the southwestern coast of Mexico. The ECMWF and UKMET as well as almost all the ECMWF ensemble members keep Nora offshore, passing just offshore of Cabo Corrientes before moving toward the entrance to the Gulf of California and Baja California Sur. However, the GFS and many of its ensemble members still show Nora moving inland over southwestern Mexico on Saturday. Overall, the multi-model track guidance consensus changed little this cycle, and so the official NHC track forecast remains very close to the previous one. The extended forecast still shows Nora moving near or over Baja California Sur and the Gulf of California on days 4 and 5. However, it is worth noting that the degree of uncertainty in this portion of the forecast is above average. The moderate northeasterly wind shear over Nora is expected to diminish over the next 12-24 h, which should allow the cyclone to intensify within a moist and unstable environment over SSTs around 29 deg C. Thus, Nora is forecast to strengthen over the next few days and become a hurricane on Saturday. Of course, this is highly dependent on Nora remaining offshore and not moving inland over mainland Mexico. Since the NHC track forecast keeps Nora offshore, the official intensity forecast lies on the high end of the intensity guidance and is closest to the ECMWF-based SHIPS and LGEM models. In this case, the normally reliable intensity consensus aids are of limited use since several of the consensus members bring Nora inland. Weakening is forecast on days 4-5 due to expected land interaction with Baja California Sur. The government of Mexico has extended the Tropical Storm Warning northward from Manzanillo to Cabo Corrientes, and issued a Tropical Storm Watch north of Cabo Corrientes to San Blas. Additional watches and warnings may be required on Friday. Key Messages: 1. Nora is forecast to strengthen to a hurricane on Saturday while it is near the coast of southwestern Mexico, and a hurricane watch and tropical storm warning are in effect for portions of that area. Interests along the southwestern coast of Mexico should closely monitor the progress of this system and updates to the forecast. 2. Heavy rain associated with Tropical Storm Nora is expected across coastal sections of the Mexican states of Oaxaca, Guerrero, Michoacan, Colima, and Jalisco. Life-threatening flash flooding and mudslides may occur. 3. Nora is forecast to be near or over the southern portion of Baja California Sur as a hurricane early next week, bringing a risk of wind and rain impacts to that area. 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 27/0300Z 14.1N 102.6W 40 KT 45 MPH 12H 27/1200Z 14.9N 103.6W 45 KT 50 MPH 24H 28/0000Z 16.3N 104.7W 55 KT 65 MPH 36H 28/1200Z 18.0N 105.6W 60 KT 70 MPH 48H 29/0000Z 19.9N 106.5W 65 KT 75 MPH 60H 29/1200Z 21.5N 107.5W 70 KT 80 MPH 72H 30/0000Z 22.7N 108.7W 75 KT 85 MPH 96H 31/0000Z 24.4N 110.6W 65 KT 75 MPH...NEAR BAJA CAL SUR 120H 01/0000Z 26.0N 112.1W 45 KT 50 MPH...OVER BAJA CAL SUR $$ Forecaster Reinhart/Cangialosi

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Tropical Storm Ida Forecast Discussion Number 2

2021-08-26 22:51:12| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Thu Aug 26 2021 000 WTNT44 KNHC 262051 TCDAT4 Tropical Depression Nine Discussion Number 2 NWS National Hurricane Center Miami FL AL092021 500 PM EDT Thu Aug 26 2021 The overall satellite presentation of the tropical cyclone has continued to gradually improve today. Visible imagery and very recent observations from an Air Force Reserve reconnaissance aircraft indicate that the circulation has continued to become better defined. In addition, the convective activity has become a little better organized in a band around the northeastern and eastern portions of the circulation, and the system is likely near tropical storm strength. However, the initial intensity remains 30 kt pending the aircraft fully sampling the eastern portion of the circulation. The initial motion estimate is northwestward or 325/12 kt. The 1200 UTC dynamical model guidance continues to take the system northwestward around the southwestern side of well-established deep-layer ridge over the western Atlantic. On the forecast track, the system is expected to move over portions of western Cuba late Friday, over the southeastern and central Gulf of Mexico on Saturday, and approach the northern Gulf coast on Sunday. Although the track guidance envelope has tightened this cycle, increasing confidence in the overall forecast scenario, some shifts in the track are still likely until the system consolidates and becomes better defined. Users are reminded to not focus on the exact forecast track as storm surge, wind, and rainfall hazards will extend far from the center, and the average NHC track forecast error at day 3 is around 120 miles. The lastest NHC track forecast is close to the previous official forecast, and lies between the TCVA and HCCA consensus aids. There is some evidence of some light to moderate southerly shear over the system, but with the cyclone moving over the high ocean heat content waters of the northwestern Caribbean Sea the shear should not hinder intensification, with steady strengthening anticipated during the next 12 to 24 hours. Once the system moves over the Gulf of Mexico, it will be traversing a warm eddy, and this feature, combined with a favorable upper-level wind pattern and a moist atmosphere, is likely to result in steady to rapid strengthening on Saturday and Saturday night. The NHC intensity forecast again brings the system to near major hurricane strength when it approaches the northern Gulf coast on Sunday. This is supported by the HWRF and CTCI models, and the global model guidance that has consistently showed significant deepening of the system over the Gulf of Mexico over the past several model cycles. Therefore, as mentioned this morning, there is higher-than-normal confidence that a strengthening tropical cyclone will be moving over the Gulf of Mexico this weekend. Key Messages: 1. Tropical storm conditions are expected in portions of the Cayman Islands tonight and in portions of western Cuba and the Isle of Youth Friday. Dangerous storm surge is possible Friday in portions of western Cuba, including the Isle of Youth, in areas of onshore flow. 2. Life-threatening heavy rains, flash flooding and mudslides are expected across Jamaica, the Cayman Islands, and western Cuba, including the Isle of Youth. 3. The system is forecast to approach the northern Gulf coast at or near major hurricane intensity on Sunday, where there is an increasing risk of life-threatening storm surge, damaging hurricane-force winds, and heavy rainfall Sunday and Monday, especially along the coast of Louisiana. Storm Surge and Hurricane watches will likely be issued for a portion of this area later tonight or Friday morning. Interests in these areas should closely monitor the progress of this system and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 18.0N 79.8W 30 KT 35 MPH 12H 27/0600Z 19.7N 81.0W 45 KT 50 MPH 24H 27/1800Z 21.7N 82.8W 55 KT 65 MPH...INLAND 36H 28/0600Z 23.7N 84.8W 60 KT 70 MPH...OVER WATER 48H 28/1800Z 25.6N 87.0W 70 KT 80 MPH 60H 29/0600Z 27.2N 88.8W 85 KT 100 MPH 72H 29/1800Z 28.9N 90.4W 95 KT 110 MPH 96H 30/1800Z 31.9N 91.4W 50 KT 60 MPH...INLAND 120H 31/1800Z 34.6N 90.0W 25 KT 30 MPH...INLAND $$ Forecaster Brown

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Tropical Storm Nora Forecast Discussion Number 5

2021-08-26 22:38:06| National Hurricane Center (East Pacific)

Issued at 400 PM CDT Thu Aug 26 2021 000 WTPZ44 KNHC 262037 TCDEP4 Tropical Storm Nora Discussion Number 5 NWS National Hurricane Center Miami FL EP142021 400 PM CDT Thu Aug 26 2021 Scatterometer data from around midday showed that Nora has an expansive circulation with tropical-storm-force winds nearly reaching the coast of Mexico. The data also showed a possible center embedded within a larger area of light winds, but it is possible that there's another similar feature farther west where the instrument did not sample. Nora's winds remain 35 kt based on the ASCAT pass and the latest Dvorak fixes from TAFB and SAB, and the center has been placed between the two dumb-belling vorticity maxima. Even with the updated position, Nora is moving toward the west-northwest (285/8 kt), to the south of mid-level ridging over the southern United States. A shortwave trough currently over the northern Rockies is expected to erode the ridge over the next 12-24 hours, allowing Nora to turn toward the northwest and then north-northwest by the weekend. Even with the GFS's solution of multiple swirls consolidating over the next day or so, the 12Z run shifted left and now shows Nora potentially moving inland over Mexico farther west than it had in previous runs. A few of the other models--for example the HWRF and HMON--also bring the center inland as well, but the bulk of the interpolated model trackers continue to keep Nora just offshore but very near the coast of southwestern Mexico in about 48 hours. Model spread remains larger than normal, but no significant changes were required from the previous NHC track forecast based on the latest guidance suite. After passing southwestern Mexico, Nora is expected to be over Baja California Sur or the Gulf of California on days 4 and 5. Moderate northeasterly shear continues to affect Nora, but that shear is expected to decrease to a less-intrusive magnitude during the next 24 hours. Along with warm sea surface temperatures of 28-30 degrees Celsius, a moist mid-level environment, and upper-level divergence, Nora is expected to strengthen in the coming days. The rate of intensification could, however, be tempered by Nora's large size and structure. Assuming Nora does not move inland over southwestern Mexico, the storm is expected to become a hurricane on Saturday and then possibly continue strengthening up until the point it reaches the Baja California Peninsula. Much of the intensity guidance is based on scenarios showing Nora moving inland, which is suppressing the intensity consensus aids. Therefore, the NHC intensity forecast is mostly based on the ECMWF-based SHIPS and LGEM models, since the parent ECMWF model does not show Nora moving inland. Given Nora's larger wind field, tropical-storm-force winds are likely to reach the coast of Mexico earlier than expected. Therefore, the government of Mexico has issued a Tropical Storm Warning for a portion of the southwestern coast of Mexico. The Hurricane Watch issued earlier today also remains in effect. Key Messages: 1. Nora is forecast to strengthen to a hurricane by Saturday while it is near the coast of southwestern Mexico, and a hurricane watch and tropical storm warnings are in effect for portions of that area. Interests along the southwestern coast of Mexico should closely monitor the progress of this system and updates to the forecast. 2. Heavy rain associated with Nora is expected across coastal sections of the Mexican states of Oaxaca, Guerrero, Michoacan, Colima, and Jalisco. As a result, life-threatening flash flooding and mudslides could occur. 3. Nora is forecast to be near the southern portion of Baja California Sur as a hurricane early next week, bringing a risk of wind and rain impacts to that area. Given the above average uncertainty in the forecast, it is too soon to determine the magnitude and location of these potential impacts. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 13.4N 101.7W 35 KT 40 MPH 12H 27/0600Z 14.1N 102.7W 40 KT 45 MPH 24H 27/1800Z 15.3N 103.8W 50 KT 60 MPH 36H 28/0600Z 16.8N 104.7W 55 KT 65 MPH 48H 28/1800Z 18.6N 105.6W 65 KT 75 MPH 60H 29/0600Z 20.3N 106.7W 70 KT 80 MPH 72H 29/1800Z 21.6N 107.9W 75 KT 85 MPH 96H 30/1800Z 23.6N 110.0W 75 KT 85 MPH...OVER BAJA CAL SUR 120H 31/1800Z 25.2N 111.7W 55 KT 65 MPH...OVER BAJA CAL SUR $$ Forecaster Berg

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