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Tropical Depression Nine Forecast Discussion Number 1

2021-08-26 16:56:29| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Thu Aug 26 2021 000 WTNT44 KNHC 261456 TCDAT4 Tropical Depression Nine Discussion Number 1 NWS National Hurricane Center Miami FL AL092021 1100 AM EDT Thu Aug 26 2021 Early morning visible satellite imagery shows that the circulation associated with the area of low pressure over west-central Caribbean Sea has become better defined. There has also been an increase in the organization of the associated convective activity, and based on consensus Dvorak T-numbers of 2.0 from TAFB and SAB, advisories are being initiated on a tropical depression. The initial intensity is set at 30 kt, in agreement with the subjective satellite estimates. The official reporting station in Kingston, Jamaica, has reported sustained winds of 25 kt with gusts to 35 kt during the past couple of hours. An Air Force Reserve reconnaissance aircraft is scheduled to be in the system later this afternoon to provide more information on the system's structure and intensity. The depression is moving northwestward or 325/11 kt, however the initial motion is a bit more uncertain than normal since the low- level center has only recently formed. The cyclone is forecast to move steadily northwestward around the southwestern portion of a deep-layer ridge centered over the western Atlantic. This track should bring the center near or over western Cuba late Friday, over the southeastern and central Gulf of Mexico Friday night and Saturday, and have the center approach the northern Gulf coast on Sunday. The track guidance is in relatively good agreement, however the average NHC track forecast error at day 4 is around 175 miles, so users should not focus on the details of the long range track forecast. Some shifts in the track are likely until the system consolidates and becomes better defined. The NHC track is near the various consensus model aids and is in best agreement with the GFS ensemble mean. The depression will be moving over the high ocean heat content waters of the northwestern Caribbean Sea during the next 24-36 hours. This, in combination with low vertical wind shear and a moist environment, should allow for steady strengthening. The depression is forecast to become a tropical storm later today or tonight, and could approach hurricane strength as it passes near or over western Cuba. Once the system moves into the Gulf of Mexico, conditions are expected to be conducive for additional strengthening, and rapid intensification is explicitly shown in the NHC forecast between 48 and 72 hours. The NHC intensity forecast brings the system near major hurricane strength when it approaches the northern Gulf coast on Sunday. This forecast is supported by the HWRF and CTCI models, and the GFS, ECMWF, and UKMET global model guidance, which all significantly deepen the cyclone over the Gulf of Mexico. As a result, there is higher-than-normal confidence that a strengthening tropical cyclone will be moving over the Gulf this weekend. Key Messages: 1. Tropical storm conditions are likely in portions of the Cayman Islands tonight and western Cuba Friday and Friday night, with dangerous storm surge possible in portions of western Cuba, including the Isle of Youth, in areas of onshore flow. 2. The system is expected to produce life-threatening heavy rains, flash flooding and mudslides across Jamaica, the Cayman Islands, western Cuba, including the Isle of Youth and northeastern portions of the Yucatan Peninsula. 3. This system is forecast to approach the northern Gulf Coast at or near major hurricane intensity on Sunday, although the forecast uncertainty is larger than usual since the system is just forming. There is a risk of life-threatening storm surge, damaging hurricane-force winds, and heavy rainfall Sunday and Monday along the northern Gulf Coast from the Florida Panhandle to the upper Texas coast, with the greatest risk along the coast of Louisiana. Interests in these areas should closely monitor the progress of this system and ensure they have their hurricane plan in place. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 16.9N 79.2W 30 KT 35 MPH 12H 27/0000Z 18.2N 80.4W 35 KT 40 MPH 24H 27/1200Z 20.3N 82.0W 45 KT 50 MPH 36H 28/0000Z 22.5N 83.9W 55 KT 65 MPH...INLAND 48H 28/1200Z 24.4N 86.0W 65 KT 75 MPH...OVER WATER 60H 29/0000Z 26.1N 88.1W 80 KT 90 MPH 72H 29/1200Z 27.7N 90.0W 95 KT 110 MPH 96H 30/1200Z 30.5N 92.0W 70 KT 80 MPH...INLAND 120H 31/1200Z 33.7N 91.2W 30 KT 35 MPH...INLAND $$ Forecaster Brown

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Tropical Storm Nora Forecast Discussion Number 4

2021-08-26 16:47:29| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Thu Aug 26 2021 373 WTPZ44 KNHC 261447 TCDEP4 Tropical Storm Nora Discussion Number 4 NWS National Hurricane Center Miami FL EP142021 1000 AM CDT Thu Aug 26 2021 Satellite images show that deep convection embedded within the sprawling circulation of the depression is gradually becoming better organized, and 91-GHz SSMIS data from 1117 UTC showed improved curvature to the bands, especially within the western semicircle. Subjective Dvorak estimates are now a consensus T2.5/35 kt from TAFB and SAB, while objective numbers from UW-CIMSS are running a little higher. Therefore, the depression is being upgraded to Tropical Storm Nora with 35-kt winds. The microwave data, as well as first-light visible imagery, suggest that the center may be consolidating or re-forming a little farther east of where we had been tracking it. Nora is moving slowly toward the west-northwest (296/6 kt), steered by a strong mid-level ridge located over the southern United States. This ridge is expected to dissolve over the next 24 hours as a shortwave trough moves across the Rocky Mountains, allowing Nora to turn toward the northwest and north-northwest through the weekend. Most of the differences among the track models still appear to be related to the initial location of Nora's center. The GFS continues to show the system having multiple low-level vortices, with a dominant one forming well to the east and moving inland along the southwestern coast of Mexico as early as late Friday, and many more GEFS ensemble members show a similar scenario compared to yesterday. The HWRF and HMON are also in the camp of bringing Nora's center inland over Mexico. Other models, including the ECMWF (and most of its ensemble members), the UKMET, and the consensus aids, still show Nora's center staying just offshore. The new NHC track forecast has been shifted eastward, primarily due to the adjustment of the initial position, and shows Nora's center very close to the coast of southwestern Mexico over the weekend. If Nora's center re-forms, then additional shifts in the track forecast will be likely. By early next week, Nora is likely to head towards Baja California Sur, but here is still a lot of uncertainty on the exact track at that time. Moderate northeasterly vertical shear continues to affect Nora, but this shear is expected to decrease to 10 kt or less in 36-48 hours. In addition, the storm will be moving over warm waters of 28-29 degrees Celsius and through an environment of high mid-level moisture. These factors should allow for continued strengthening, although the system's large size could be one limiting factor in how fast that strengthening happens. Nora is expected to be near or at hurricane strength when it approaches the coast of southwestern Mexico in 2-3 days. However, the intensity forecast, especially on days 3-5, hinges on whether or not the center moves inland. If it does not, Nora will have greater opportunity to strengthen while it heads toward the Baja California Peninsula. Since several of the intensity models assume a scenario where Nora moves inland, the NHC intensity forecast more closely follows the no-land versions of the GFS and ECMWF SHIPS models through day 4 to be consistent with what is shown in the track forecast. Given the high uncertainty in Nora's future track, and its roughly shore-parallel path, a larger-than-normal hurricane watch area has been issued for the southwestern coast of Mexico by the Mexican government. Key Messages: 1. Nora is forecast to strengthen to a hurricane by late Saturday while it approaches the coast of southwestern Mexico, and hurricane and tropical storm watches are now 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 26/1500Z 12.5N 100.8W 35 KT 40 MPH 12H 27/0000Z 13.2N 101.9W 40 KT 45 MPH 24H 27/1200Z 14.3N 103.0W 50 KT 60 MPH 36H 28/0000Z 15.7N 103.7W 55 KT 65 MPH 48H 28/1200Z 17.4N 104.5W 60 KT 70 MPH 60H 29/0000Z 19.0N 105.3W 65 KT 75 MPH 72H 29/1200Z 20.2N 106.3W 70 KT 80 MPH 96H 30/1200Z 22.3N 108.6W 75 KT 85 MPH 120H 31/1200Z 24.0N 110.5W 55 KT 65 MPH...INLAND $$ Forecaster Berg

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Tropical Depression Fourteen-E Forecast Discussion Number 3

2021-08-26 10:38:24| National Hurricane Center (East Pacific)

Issued at 400 AM CDT Thu Aug 26 2021 000 WTPZ44 KNHC 260838 TCDEP4 Tropical Depression Fourteen-E Discussion Number 3 NWS National Hurricane Center Miami FL EP142021 400 AM CDT Thu Aug 26 2021 Satellite imagery indicates that convection is increasing near the center of Tropical Depression Fourteen-E, but it is occurring in bands that are not showing a lot of curvature at this time. Satellite intensity estimates are currently 35 kt from SAB and 30 kt from TAFB, and the CIMSS ADT and satellite consensus techniques are also in the 30-35 kt range. In addition, earlier scatterometer data showed 25-30 kt winds, although there was no data close to the center. The initial intensity remains 30 kt for this advisory. The initial motion is a somewhat uncertain 290/7 kt. The cyclone is being steered generally westward along the southern extent of a mid-level ridge over the south-central United States. A deep-layer trough over the western U.S. is forecast to weaken this ridge during the next couple of days, with the cyclone moving northwestward to north-northwestward as a result. The track guidance continues to show a motion close to the coast of southwestern Mexico between 48-72 h, and the GFS and Canadian models on the eastern side of the guidance show a landfall in Mexico. The ECMWF model is farther to the left and keeps the system offshore of Mexico, while the UKMET is between these extremes and keeps the center offshore of mainland Mexico before taking the system near the southern portion of the Baja California peninsula. The forecast track is similar to the previous track, following the consensus models in keeping the center offshore of mainland Mexico before coming near Baja California Sur. However, there remains above average uncertainty in the track forecast, and interests along the coast of southwestern Mexico and in Baja California Sur should closely monitor the progress of the system and potential changes to the forecast. The depression is currently being affected by northeasterly vertical shear, which is likely to persist for another 24 h. After that time, conditions appear favorable for strengthening if the center stays far enough offshore. The new intensity forecast is similar to the previous forecast, and it lies near the upper edge of the intensity guidance. The 48-120 h portion of the forecast again has lower than average confidence due to the possibility of land interaction. Key Messages: 1. The depression is forecast to strengthen to a tropical storm on Thursday and be near hurricane intensity by Saturday or Saturday night. While the core of the storm is currently expected to pass near but offshore the southwestern coast of Mexico, strong winds and heavy rainfall, possibly resulting in flash floods and mudslides, could affect portions of that area over the next several days. Interests in this area should closely monitor the progress of this system and updates to the forecast. 2. The system is forecast to pass 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 26/0900Z 12.0N 100.6W 30 KT 35 MPH 12H 26/1800Z 12.8N 101.5W 35 KT 40 MPH 24H 27/0600Z 13.9N 102.8W 40 KT 45 MPH 36H 27/1800Z 15.2N 104.2W 45 KT 50 MPH 48H 28/0600Z 16.5N 105.1W 55 KT 65 MPH 60H 28/1800Z 18.0N 105.7W 60 KT 70 MPH 72H 29/0600Z 19.5N 106.3W 65 KT 75 MPH 96H 30/0600Z 21.5N 108.5W 70 KT 80 MPH 120H 31/0600Z 23.5N 111.0W 55 KT 65 MPH $$ Forecaster Beven

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Tropical Depression Fourteen-E Forecast Discussion Number 2

2021-08-26 04:43:50| National Hurricane Center (East Pacific)

Issued at 1000 PM CDT Wed Aug 25 2021 000 WTPZ44 KNHC 260243 TCDEP4 Tropical Depression Fourteen-E Discussion Number 2 NWS National Hurricane Center Miami FL EP142021 1000 PM CDT Wed Aug 25 2021 Recent satellite imagery and microwave data indicate that the depression has not become better organized this evening. It is producing a ragged area of convection over the northwestern portion of its circulation, which appears somewhat elongated along an east-west axis. The latest UW-CIMSS objective ADT estimate and subjective 00z Dvorak classifications from TAFB and SAB support an initial intensity of 30 kt for this advisory. The estimated initial motion of the poorly organized depression is an uncertain 280/6 kt. The cyclone is being steered generally westward along the southern extent of a mid-level ridge over the south-central United States. A deep-layer trough over the western U.S. is forecast to weaken the steering ridge during the next couple of days. Thus, the depression is forecast to gain some latitude and move west-northwestward overnight and Thursday, and then northwestward or north-northwestward on Friday and Saturday. Although the track guidance consensus and many GEFS and ECMWF ensemble members still keep the center of the cyclone offshore, there was a pronounced eastward shift in the guidance envelope this cycle. In fact, the GFS and several GEFS members show the system moving inland along the coast of southwestern Mexico in 2-3 days. The official NHC track forecast has been adjusted to the right of the previous one from 48 h onward and lies along the HFIP corrected consensus approach (HCCA) aid. This brings the center of the cyclone closer to the coast of southwestern Mexico, but remains offshore and to the left of much of the latest guidance. The extended forecast takes the system near the southern portion of Baja California Sur early next week, but overall there is above average uncertainty in the extended portion of the track forecast. Interests along the coast of southwestern Mexico and in Baja California Sur should closely monitor future updates to the forecast. The depression is located within a favorable thermodynamic environment for strengthening, but moderate to strong northeasterly vertical wind shear should limit its intensification rate in the short-term period. The shear is expected to weaken by Friday, and the system is forecast to become a hurricane this weekend over very warm SSTs. There remains a large amount of spread in the intensity guidance beyond 48 h, due to the potential for land interaction earlier in the forecast period. Since the latest NHC track forecast keeps the system offshore, the intensity forecast is much higher than the consensus aids during this period and trends toward the stronger statistical-dynamical guidance. Again, confidence is lower than normal in the day 3-5 forecast. Key Messages: 1. The depression is forecast to strengthen to a tropical storm on Thursday and be near hurricane intensity by Saturday. While the core of the storm is currently expected to pass near but offshore the southwestern coast of Mexico, strong winds and heavy rainfall, possibly resulting in flash floods and mudslides, could affect portions of that area over the next several days. Interests in this area should closely monitor the progress of this system and updates to the forecast. 2. The system is forecast to pass 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 26/0300Z 11.9N 100.1W 30 KT 35 MPH 12H 26/1200Z 12.3N 101.2W 35 KT 40 MPH 24H 27/0000Z 13.1N 102.7W 40 KT 45 MPH 36H 27/1200Z 14.2N 103.9W 45 KT 50 MPH 48H 28/0000Z 15.6N 104.8W 55 KT 65 MPH 60H 28/1200Z 17.2N 105.6W 60 KT 70 MPH 72H 29/0000Z 18.8N 106.5W 65 KT 75 MPH 96H 30/0000Z 21.3N 108.7W 70 KT 80 MPH 120H 31/0000Z 23.0N 111.0W 60 KT 70 MPH $$ Forecaster Reinhart/Pasch

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Tropical Depression Fourteen-E Forecast Discussion Number 1

2021-08-25 22:50:41| National Hurricane Center (East Pacific)

Issued at 400 PM CDT Wed Aug 25 2021 000 WTPZ44 KNHC 252050 TCDEP4 Tropical Depression Fourteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP142021 400 PM CDT Wed Aug 25 2021 Scatterometer data from a few hours ago revealed that a small but sufficiently well-defined circulation has formed on the western end of a broader circulation which lies a few hundred miles south of the southern coast of Mexico. Although the system is still in its formative stages and banding features are not readily apparent, Dvorak estimates from TAFB and SAB have been a consensus T2.0/30 kt since this morning. The system is therefore now designated as a 30-kt tropical depression, although the scatterometer data suggested that its winds are already very near tropical storm force. The depression's surface center apparently formed a little south of the vorticity maximum we have been tracking over the past day or so. Therefore, the initial motion is very uncertain but is estimated to be westward, or 275/7 kt. The evolution of the steering pattern is fairly consistent among the models. A strong mid-tropospheric high over the U.S. Southern Plains is forecast to weaken over the next couple of days, causing the depression to turn from a westward motion now, to a west-northwest motion tonight, to a northwest and north-northwest motion by Friday and Saturday. On this track, most of the models bring the center of the system near but still offshore the southwestern coast of Mexico. The GFS has been a notable exception, bringing the system inland over southwestern Mexico in about 3 days. However, that model shows a complex interaction with multiple low-level centers that consolidate farther east, and most of the GEFS ensemble members remain offshore with the other deterministic models. As a result, this first NHC official forecast also shows a track remaining offshore and is a little to the left of the HCCA and TVCE consensus aids. Moderate easterly to northeasterly shear is likely to continue over the depression for the next day or so, which would temper any fast strengthening in the short term. Still, the system will be moving over warm waters of 28-29 degrees Celsius over the next few days, and lower shear in 2-3 days should allow it to strengthen to a hurricane by the weekend as it passes near the southwestern coast of Mexico and approaches the southern part of the Baja California peninsula. The intensity guidance is in fairly good agreement during the first 2 days, but there is much more spread after that time, likely related to the degree of land interaction. The NHC intensity forecast is near the consensus aids during the first 3 days and then a little bit above them on days 4 and 5, lying between the HWRF and HMON models at those forecast times. Key Messages: 1. The depression is forecast to strengthen to a tropical storm tonight and be near hurricane intensity by Saturday. While the core of the storm is currently expected to remain offshore of the southwestern coast of Mexico, strong winds and heavy rainfall, possibly resulting in flash floods and mudslides, could affect portions of that area over the next several days. 2. The system is expected to pass near the southern portion of Baja California Sur as a hurricane Sunday and Monday, bringing a risk of wind and rain impacts to that area early next week. Given the uncertainty in the forecast, it is too soon to determine the magnitude and location of these potential impacts, but interests in this area should monitor the progress of this system and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 11.7N 99.4W 30 KT 35 MPH 12H 26/0600Z 12.0N 100.4W 35 KT 40 MPH 24H 26/1800Z 12.8N 102.1W 40 KT 45 MPH 36H 27/0600Z 13.6N 103.7W 45 KT 50 MPH 48H 27/1800Z 14.7N 105.0W 55 KT 65 MPH 60H 28/0600Z 16.2N 106.0W 60 KT 70 MPH 72H 28/1800Z 18.0N 106.9W 65 KT 75 MPH 96H 29/1800Z 21.1N 109.6W 75 KT 85 MPH 120H 30/1800Z 22.7N 112.1W 65 KT 75 MPH $$ Forecaster Berg

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