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Tropical Depression Eta Forecast Discussion Number 18

2020-11-05 03:38:42| National Hurricane Center (Atlantic)

Issued at 900 PM CST Wed Nov 04 2020 000 WTNT44 KNHC 050238 TCDAT4 Tropical Depression Eta Discussion Number 18 NWS National Hurricane Center Miami FL AL292020 900 PM CST Wed Nov 04 2020 The rugged terrain of Central America is taking a toll on Eta. The low-level circulation is losing definition, and deep convection is well removed from the center. Eta was downgraded to a 30-kt tropical depression a few hours ago, and the initial intensity is held at that value for this advisory. The strongest winds are likely occurring offshore over the Gulf of Honduras, as noted in earlier ASCAT scatterometer surface wind data. Eta, or its remnant low, is forecast to move west-northwestward to northwestward during the next 12 to 24 hours, taking the cyclone across portions of Honduras during that time. In 24 to 36 hours, a turn to the north and then northeast is forecast as Eta feels some influence from a mid- to upper level trough moving over the northwestern Gulf of Mexico. As this trough slides southeastward across the Gulf, it should steer Eta northeastward at a faster forward speed toward Cuba, likely approaching that country late Saturday or Sunday. After that time, the models show Eta rotating around the north side of the trough (or cut-off low) in the vicinity of south Florida and the Florida Keys late this weekend and early next week. There is still a lot of spread in the model tracks at the 96- and 120-hour time periods, which is not surprising given the expected complex steering pattern. The NHC track forecast is adjusted a little to the east of the previous one to come into better agreement with the latest models, but confidence in the details of the extended track forecast is low. Continued weakening is expected while Eta remains inland over the rugged terrain of Central America, and the cyclone will likely degenerate into a remnant low or trough of low pressure on Thursday. Whatever is left of Eta, and the broad gyre that it is embedded within, will move offshore of Belize over the northwestern Caribbean Sea by Thursday night or Friday. The rate of intensification over the northwestern Caribbean Sea will likely be gradual because of the mixed environmental conditions. On one hand, Eta will be moving over warm water and in a region of upper-level diffluence, which should support convective growth and strengthening. Conversely, there will also be an increase in wind shear and the cyclone is likely to have a broad structure, which should prevent rapid intensification. The net result will likely be slow but steady strengthening, and Eta is forecast to be a strong tropical storm when it is near south Florida. The models are in fair agreement on Eta's future intensity, and this forecast is just a little higher than the previous one. Key Messages: 1. Through Monday morning, heavy rainfall from Eta will lead to catastrophic, life-threatening flash flooding and river flooding across portions of Central America, along with landslides in areas of higher terrain. Flash and river flooding is also possible across Jamaica, southeast Mexico, the Cayman Islands and western Cuba. 2. Eta is forecast to regain tropical storm strength over the northwestern Caribbean Sea late this week. Although the details of the future track and intensity of Eta are uncertain, there is an increasing risk of impacts from wind and rainfall in portions of Cuba, southern Florida and the Florida Keys this weekend and early next week. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 14.2N 86.3W 30 KT 35 MPH...INLAND 12H 05/1200Z 15.0N 87.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 06/0000Z 16.1N 87.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 06/1200Z 17.2N 86.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 07/0000Z 18.2N 85.5W 35 KT 40 MPH...TROPICAL CYCLONE 60H 07/1200Z 19.3N 83.7W 40 KT 45 MPH 72H 08/0000Z 20.4N 82.0W 45 KT 50 MPH 96H 09/0000Z 23.3N 79.9W 50 KT 60 MPH 120H 10/0000Z 24.7N 81.4W 55 KT 65 MPH $$ Forecaster Cangialosi

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Tropical Storm Odalys Forecast Discussion Number 6

2020-11-05 03:36:12| National Hurricane Center (East Pacific)

Issued at 700 PM PST Wed Nov 04 2020 000 WTPZ45 KNHC 050236 TCDEP5 Tropical Storm Odalys Discussion Number 6 NWS National Hurricane Center Miami FL EP202020 700 PM PST Wed Nov 04 2020 Odalys has devolved into a sheared tropical cyclone, with the bulk of the deep convection displaced to the northeast of the now fully exposed low-level circulation center. The initial intensity has been held at 40 kt based on a blend of Dvorak satellite current intensity (CI) estimates of T3.0/45 kt from TAFB and T2.5/35 kt from SAB. A 04/2142 UTC UW-CIMSS SATCON estimate of 40 kt also supports this intensity. Odalys is now moving west-northwestward, or 295/09 kt. The cyclone is expected to gradually turn more westward during the next 24 hours or so, followed by a turn toward the west as Odalys degenerates into a shallow low pressure system. By 48 hours and beyond, the remnant low is forecast to move west-southwestward to southwestward under the influence of low-level northeasterly trade wind flow. The NHC track forecast is similar to the previous advisory track, and lies close to the simple-consensus track model, TVCE. The current southwesterly deep-layer vertical wind shear of near 30 kt is forecast to steadily increase to 40 kt during the next 72 hours. Sea-surface temperatures decreasing to less than 26 deg C will also help hasten the weakening process during that time, resulting in Odalys becoming a remnant low in about 36 hours, followed by dissipation in 96 hours, if not sooner. The NHC intensity forecast is similar to the previous advisory, and closely follows the simple-consensus intensity models IVCN and ICON. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 18.1N 121.7W 40 KT 45 MPH 12H 05/1200Z 18.7N 123.0W 35 KT 40 MPH 24H 06/0000Z 18.9N 124.6W 30 KT 35 MPH 36H 06/1200Z 18.6N 125.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 07/0000Z 17.9N 127.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 07/1200Z 17.0N 128.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 08/0000Z 16.2N 129.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 09/0000Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Eta Forecast Discussion Number 17

2020-11-04 21:46:35| National Hurricane Center (Atlantic)

Issued at 300 PM CST Wed Nov 04 2020 000 WTNT44 KNHC 042046 TCDAT4 Tropical Storm Eta Discussion Number 17 NWS National Hurricane Center Miami FL AL292020 300 PM CST Wed Nov 04 2020 Eta continues to weaken as it moves from Nicaragua into Honduras. There is little convection left near the center, and the strongest convection remains in bands well removed from the center. As before, there are no wind observations available near the center of Eta at this time, so the initial intensity is reduced to a uncertain 35 kt. The initial motion is westward or 275/6. A mid-level ridge to the north of the cyclone should steer it on a generally west- northwestward track during the next 24 h or so. After that time, a mid- to upper-level trough moving over the central and eastern Gulf of Mexico is expected to cause Eta or is remnants to turn northward and then northeastward, Then, by 120 h, the cyclone is likely to move northward or northwestward on the eastern side of the trough as it cuts off into a closed low. The track guidance remains in reasonable agreement with this scenario, However, there remains some spread on when and where the various turns will occur, and there has also been an eastward shift in the guidance envelope after 36 h. The new forecast track is shifted to the east of the previous track after 36 h, and at 72 and 96 h it lies a little to the west of the various consensus models, Eta will continue to weaken while it crosses Honduras, and it is expected to decay to a remnant low before it reaches the Gulf of Honduras or the northwestern Caribbean Sea. Re-development is expected once the center is over the water. However, interaction with the aforementioned trough could result in a structure that is more subtropical or hybrid, as suggested by the UKMET, than a classical tropical cyclone, as suggested by the ECMWF. The new intensity forecast will follow the previous forecast and go with a gradual intensification that follows the general trend of the model guidance. However, the intensity forecast again lies a little below the intensity consensus. Although it is weakening, Eta will continue to produce heavy rainfall and flooding over portions of Central America. Key Messages: 1. Through Monday morning, heavy rainfall from Eta will lead to catastrophic, life-threatening flash flooding and river flooding across portions of Central America, along with landslides in areas of higher terrain. Flash and river flooding is also possible across Jamaica, southeast Mexico, the Cayman Islands and western Cuba. 2. Eta is forecast to regain tropical storm strength before it moves across portions of Cuba and approaches southern Florida this weekend. While it is too soon to determine the exact timing, magnitude, and location of possible impacts from wind and rainfall, interests in Cuba, southern Florida and the Florida Keys should monitor the progress of Eta through the week. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 13.9N 85.7W 35 KT 40 MPH...INLAND 12H 05/0600Z 14.2N 86.7W 30 KT 35 MPH...INLAND 24H 05/1800Z 15.1N 87.8W 25 KT 30 MPH...POST-TROP/INLAND 36H 06/0600Z 16.5N 87.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 06/1800Z 17.7N 86.7W 30 KT 35 MPH...TROPICAL CYCLONE 60H 07/0600Z 18.8N 84.8W 40 KT 45 MPH 72H 07/1800Z 20.5N 82.6W 45 KT 50 MPH 96H 08/1800Z 24.0N 80.5W 50 KT 60 MPH 120H 09/1800Z 25.5N 82.5W 50 KT 60 MPH $$ Forecaster Beven

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Tropical Storm Odalys Forecast Discussion Number 5

2020-11-04 21:36:08| National Hurricane Center (East Pacific)

Issued at 100 PM PST Wed Nov 04 2020 000 WTPZ45 KNHC 042036 TCDEP5 Tropical Storm Odalys Discussion Number 5 NWS National Hurricane Center Miami FL EP202020 100 PM PST Wed Nov 04 2020 The center of Odalys has become easier to find this afternoon. A well-defined low-level center has become apparent on visible satellite imagery, about 50 nm southwest of the deepest convection. Despite this somewhat disheveled appearance, a series of ASCAT passes earlier this afternoon found winds of 35-40 kt in a band north of the center. Allowing for a bit of instrument undersampling, and blending the latest SAB and TAFB satellite estimates, the initial intensity was raised slightly to 40 kt for this advisory. Odalys continues to move northwestward this afternoon at 315/15 kt. The track forecast philosophy has remained largely unchanged. The storm will continue to head northwest in the short-term, situated between a deep-layer ridge over Mexico and a mid to upper-level trough located to its northeast. This same trough will likely generate high enough vertical wind shear to cause the low and mid level centers of Odalys to completely separate in the next 24 h, resulting in the low-level center of Odalys to bend west and then west-southwest as it comes under the influence of the low-level easterly trade winds. The latest track guidance is in good agreement on this evolution with only minor speed differences after Odalys becomes a shallow vortex and only small adjustments were made to the official forecast track. Odalys may maintain its current intensity over the next 12 h if it is able to maintain active downshear convection. Thereafter, the southwesterly vertical wind shear is forecast to increase above 35 kt in the latest GFS-based SHIPS guidance. This should import very dry mid-level air near the center and will likely choke off any remaining convective bursts. Odalys is expected to become a shallow remnant low on Friday afternoon, if not sooner. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 17.7N 120.7W 40 KT 45 MPH 12H 05/0600Z 18.3N 122.1W 40 KT 45 MPH 24H 05/1800Z 18.8N 123.6W 35 KT 40 MPH 36H 06/0600Z 18.7N 125.2W 30 KT 35 MPH 48H 06/1800Z 18.0N 126.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 07/0600Z 17.2N 127.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/1800Z 16.3N 128.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 08/1800Z...DISSIPATED $$ Forecaster Papin/Zelinsky

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Tropical Storm Odalys Forecast Discussion Number 4

2020-11-04 15:45:09| National Hurricane Center (East Pacific)

Issued at 700 AM PST Wed Nov 04 2020 000 WTPZ45 KNHC 041444 TCDEP5 Tropical Storm Odalys Discussion Number 4 NWS National Hurricane Center Miami FL EP202020 700 AM PST Wed Nov 04 2020 Over the last 6 h Odalys has exhibited a bursting pattern with cloud tops colder than -70C occuring to the northeast of the estimated low-level center. The center itself has been a bit difficult to locate overnight but is estimated to be on the southwest edge of this recent convective activity. Satellite estimates from SAB and TAFB were 35 kt and 45 kt respectively, but the initial intensity is kept at 35 kt for this advisory out of respect for overnight ASCAT data that supported the lower value and the fact that the structure of the cyclone hasn't changed much since then. Odalys is now moving to the northwest with a similar forward motion 315/14 kt. This motion is expected to continue in the short term as the storm is being steered between a mid-level ridge centered over Northern Mexico to its northeast and a deep-layer trough centered to its northwest. After 24 h, Odalys is expect to become a shallow system as its convection gets stripped away by the deep layer trough. Its track will bend back west and then west-southwest as it comes under the influence of northeasterly trade wind flow associated with a low-level anticyclone off the southwestern US coast. The latest track guidance remains in good agreement of this evolution and only minor modifications were made to the forecast track owing to the slightly further north initial position. While small fluctuations in intensity associated with periodic convective bursts are possible today, southwesterly vertical wind shear is already increasing over the system and will soon be importing very dry mid-level air over the low-level circulation. This will ultimately lead to the tropical storm's demise as it moves over marginally warm sea surface temperatures. The intensity forecast was held at the current intensity for the first 24 h with gradual weakening thereafter. Odalys is expected to become a remnant low by Friday and dissipate entirely by the end of the weekend. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 16.9N 119.2W 35 KT 40 MPH 12H 05/0000Z 17.9N 120.8W 35 KT 40 MPH 24H 05/1200Z 18.7N 122.4W 35 KT 40 MPH 36H 06/0000Z 18.8N 124.0W 30 KT 35 MPH 48H 06/1200Z 18.4N 125.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 07/0000Z 17.6N 126.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 07/1200Z 16.6N 127.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 08/1200Z 15.5N 130.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 09/1200Z...DISSIPATED $$ Forecaster Papin/Zelinsky

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