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Tropical Storm Odalys Forecast Discussion Number 9

2020-11-05 21:54:25| National Hurricane Center (East Pacific)

Issued at 100 PM PST Thu Nov 05 2020 000 WTPZ45 KNHC 052054 TCDEP5 Tropical Storm Odalys Discussion Number 9 NWS National Hurricane Center Miami FL EP202020 100 PM PST Thu Nov 05 2020 Deep convection associated with Odalys has largely dissipated over the past 6-9 h with just a remnant swirl of low clouds surrounding the center. Satellite estimates from SAB and TAFB continue to decrease and a recent ASCAT pass confirmed that the wind field has begun to spin down, with maximum sustained winds near 35 kt. As anticipated, the combination of high southwesterly vertical wind shear greater than 30 kt and dry mid-level air around 40 percent as diagnosed from ECMWF-SHIPS guidance has lead to a collapse of deep central convection. Even though sea surface temperatures under Odalys remain marginally warm around 26 C, vertical wind shear and mid-level dry air are forecast to become even more hostile over the next 24 h. Therefore, the latest official forecast now anticipates Odalys to become a remnant low in 24 h. Degeneration to a remnant low could occur as quickly as this evening if organized deep convection does not redevelop soon. The initial motion of the cyclone is estimated near 280/6 kt, and a due westward motion is expected within the next few hours. Odalys is now a shallow cyclone, and will primarily be steered by low-level northeasterly trade wind flow, gradually bending from a west to southwest heading over the next 24-36 h. The NHC forecast track shows a slightly sharper turn to the the southwest now that the cyclone has become more shallow, but the official track remains near the track guidance consensus. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 18.5N 123.6W 35 KT 40 MPH 12H 06/0600Z 18.3N 124.6W 30 KT 35 MPH 24H 06/1800Z 17.7N 125.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 07/0600Z 17.0N 126.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 07/1800Z 16.4N 126.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 08/0600Z 15.9N 127.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 08/1800Z...DISSIPATED $$ Forecaster Papin/Zelinsky

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Tropical Depression Eta Forecast Discussion Number 21

2020-11-05 21:54:22| National Hurricane Center (Atlantic)

Issued at 300 PM CST Thu Nov 05 2020 000 WTNT44 KNHC 052054 TCDAT4 Tropical Depression Eta Discussion Number 21 NWS National Hurricane Center Miami FL AL292020 300 PM CST Thu Nov 05 2020 The low-level circulation of Eta has become disorganized to the point that the system more resembles a remnant low than a tropical cyclone. However, the system continues to produce convection in an area just north and northwest of the estimated center position, as well as in a cluster well to the northeast. Based on this, and the expectation that the system will start re-developing during the next several hours as it moves back over water, Eta is maintained as a tropical depression for this advisory. The initial intensity is increased to 30 kt based on scatterometer data, with those winds occuring well to the northeast of the center. The center appears to be just south of the northwestern coast of Honduras, and the initial motion is an uncertain 330/7. During the next 24 h, Eta should recurve northeastward in southwesterly flow between a ridge over the central Caribbean and a developing mid- to upper-level trough over the central Gulf of Mexico. This motion should persist through about 72 h. After that, the trough is forecast to become a closed low in the vicinity of western Cuba, with Eta turning to the west-northwest as it interacts or merges with the low. While the models are in good agreement with the synoptic pattern, they are in poor agreement on the details of the track. The forecast tracks show possible landfalls in Cuba anywhere between 77W-83W, and after the turn some of the tracks are as far north as southern Florida while other stay over Cuba. In addition, there is a significant speed difference between the faster GFS/HWRF/HMON and the slower Canadian/ECMWF/UKMET. The low-confidence official forecast compromises between these various extremes and is not changed much from the previous forecast. Little change in strength is expected during the next 12 h or so as Eta starts to re-organized over water. After that, gradual strengthening is expected until the system reaches Cuba in about 72 h, with the main limiting factor being increasing southwesterly shear during that time. From 72-120 h, there is a possibility that Eta will take on subtropical or hybrid characteristics as it interacts with the developing upper-level low. The intensity forecast will be held at 50 kt during that time due to this interaction. The new intensity forecast has only minor tweaks from the previous forecast. However, it lies below the bulk of the intensity guidance for the first 60 h and above the bulk of the guidance from 72-120 h. The new forecast track, intensity, and wind radii require a Tropical Storm Watch for the Cayman Islands at this time. A Tropical Storm Watch will likely be required for portions of Cuba later tonight or on Friday. 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 in a day or so. 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 the Cayman Islands, Cuba, southern Florida and the Florida Keys this weekend and early next week. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 15.7N 87.7W 30 KT 35 MPH...INLAND 12H 06/0600Z 16.4N 87.8W 30 KT 35 MPH...OVER WATER 24H 06/1800Z 18.1N 86.3W 35 KT 40 MPH 36H 07/0600Z 19.1N 84.8W 40 KT 45 MPH 48H 07/1800Z 20.1N 83.1W 45 KT 50 MPH 60H 08/0600Z 21.3N 81.5W 45 KT 50 MPH 72H 08/1800Z 22.4N 80.1W 50 KT 60 MPH...INLAND 96H 09/1800Z 23.5N 82.0W 50 KT 60 MPH...OVER WATER 120H 10/1800Z 24.5N 84.5W 55 KT 65 MPH $$ Forecaster Beven

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Tropical Storm Odalys Forecast Discussion Number 8

2020-11-05 16:04:19| National Hurricane Center (East Pacific)

Issued at 700 AM PST Thu Nov 05 2020 000 WTPZ45 KNHC 051503 CCA TCDEP5 Tropical Storm Odalys Discussion Number 8...Corrected NWS National Hurricane Center Miami FL EP202020 700 AM PST Thu Nov 05 2020 Corrected to say dissipated for the 72 h forecast. Odalys appears to be losing the battle against high vertical wind shear and dry air entrainment as an overnight convective burst has been sheared off to the northeast. Only a small region of cloud tops colder than -60 C remains about 100 nm away from the exposed low-level circulation center. The latest satellite estimates from SAB and TAFB have decreased and it is possible that Odalys has already started weakening. However, the current intensity will be held at 45 kt for this advisory out of respect for the overnight ASCAT data. The ongoing strong southwesterly vertical wind shear is forecast to continue for the foreseeable future, and dry air will continue to envelop the circulation. Marginal sea surface temperatures of 26 C may be able to support occasional convective bursts, but these should be short lived and disorganized, and the low-level wind field should gradually spin down without any organized convection. The latest intensity forecast shows Odalys becoming a remnant low by 36 h, but this may occur sooner if convection does not refire near the center. Odalys is gradually bending more westward at 285/6 kt as it decouples from convection associated with the mid-level center and begins to be influenced primarily by the low-level steering flow. A turn due west and then west-southwest is expected over the next 24 h following the northeasterly trade wind flow. The NHC forecast track is similar to the previous one and is near the track guidance consensus. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 18.3N 122.9W 45 KT 50 MPH 12H 06/0000Z 18.5N 124.0W 40 KT 45 MPH 24H 06/1200Z 18.2N 125.2W 35 KT 40 MPH 36H 07/0000Z 17.5N 126.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 07/1200Z 16.8N 126.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 08/0000Z 16.2N 127.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 08/1200Z...DISSIPATED $$ Forecaster Papin/Zelinsky

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Tropical Depression Eta Forecast Discussion Number 20

2020-11-05 15:50:54| National Hurricane Center (Atlantic)

Issued at 900 AM CST Thu Nov 05 2020 000 WTNT44 KNHC 051450 TCDAT4 Tropical Depression Eta Discussion Number 20 NWS National Hurricane Center Miami FL AL292020 900 AM CST Thu Nov 05 2020 Eta remains disorganized this morning, as visible imagery suggests that the circulation has become elongated and that multiple vorticity centers may be present inside the larger cyclonic envelope. The center position for this advisory, which is over northwestern Honduras, is closer to convection in the northwestern semicircle than was the case 6 h ago, so the cyclone is being maintained as a tropical depression at this time. The initial motion is a somewhat uncertain 305/8 kt. Eta or its remnants should move generally northwestward today, then turn northward tonight. From 24-72 h, the system should move northeastward in response to a developing mid- to upper-level trough over the central and eastern Gulf of Mexico. From 72-120 h, the trough is forecast to become a closed mid- to upper-level low in the vicinity of western Cuba, with the center of Eta likely to turn west-northwestward on the north side of the low. While the global models are in good agreement with this synoptic evolution, there is a significant spread in the forecast tracks between the fastest and farthest east GFS and the slowest and farthest west UKMET. The new forecast track lies between these extremes in best overall agreement with the ECMWF and Canadian models, and it calls for the system to be near western Cuba and the Cayman Islands in 60-72 h, and then be over the southeastern Gulf of Mexico by the end of the forecast period. Little change in strength is expected before the center moves back over the Caribbean, but there is still a chance that Eta could degenerate to a remnant low pressure area later today if the convection does not persist. Intensification is expected over the warm waters of the Caribbean Sea from 24-72 h, although this may be slowed by southwesterly shear caused by the aforementioned trough. As the trough cuts off near or over Eta between 72-120 h, the global models suggest that the system could strengthen while acquiring at least some subtropical or hybrid characteristics due to upper-level cold air entrainment. The new intensity forecast is little changed from the previous forecast, and in the latter part of the forecast period it lies near the intensity consensus. It should be noted that while Eta regaining hurricane strength cannot be ruled out, there is little support for that in the current guidance. 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 the Cayman Islands, Cuba, southern Florida and the Florida Keys this weekend and early next week. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 15.1N 87.8W 25 KT 30 MPH...INLAND 12H 06/0000Z 15.7N 88.0W 25 KT 30 MPH...INLAND 24H 06/1200Z 16.8N 87.6W 25 KT 30 MPH...OVER WATER 36H 07/0000Z 17.8N 86.2W 30 KT 35 MPH 48H 07/1200Z 19.0N 84.5W 35 KT 40 MPH 60H 08/0000Z 20.1N 83.0W 45 KT 50 MPH 72H 08/1200Z 21.3N 81.2W 50 KT 60 MPH 96H 09/1200Z 23.0N 80.0W 50 KT 60 MPH 120H 10/1200Z 24.0N 83.0W 55 KT 65 MPH $$ Forecaster Beven

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Tropical Depression Eta Forecast Discussion Number 19

2020-11-05 09:52:46| National Hurricane Center (Atlantic)

Issued at 300 AM CST Thu Nov 05 2020 000 WTNT44 KNHC 050852 TCDAT4 Tropical Depression Eta Discussion Number 19 NWS National Hurricane Center Miami FL AL292020 300 AM CST Thu Nov 05 2020 Eta has become very disorganized due to its interaction with the land mass of Central America, and may no longer have a surface circulation. Based on a few surface observations, the maximum winds are estimated to be around 25 kt over the water to the north of Honduras. Eta is likely to degenerate into a post-tropical low very soon, if it hasn't done so already. Since the low is predicted to move into the northwestern Caribbean Sea by tomorrow night, some restrengthening is forecast to begin by the weekend. However the expected broad nature of the cyclone and stronger vertical shear are likely to limit strengthening over the next several days. The official intensity forecast is similar to the latest model consensus. The center is extremely difficult to locate at this time, but based on continuity the initial motion is estimated to be 300/7 kt. Eta, or its post-tropical remnant low/trough, should continue to move over land today, and then turn northward tonight while moving along the eastern side of a broader gyre. This will take the system into the Gulf of Honduras and over the northwestern Caribbean Sea on Friday. A negatively-tilted 500-mb trough/low developing over the Gulf of Mexico should induce a generally northeastward motion for the next 2-3 days and take the cyclone across portions of Cuba in 3-4 days. Thereafter, the system is forecast to rotate cyclonically around the eastern side of the 500 mb low and turn northwestward to westward by the end of the forecast period. The official forecast is a blend of the latest GFS and ECMWF predictions, but leans toward the latter model. This track could take the system near or over portions of extreme southern Florida by late this weekend or early next week, but there is low confidence in the forecast, especially at 3-5 days. 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 05/0900Z 14.5N 87.0W 25 KT 30 MPH 12H 05/1800Z 15.0N 87.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 06/0600Z 16.2N 87.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 06/1800Z 17.4N 86.3W 35 KT 40 MPH...TROPICAL CYCLONE 48H 07/0600Z 18.5N 84.7W 40 KT 45 MPH 60H 07/1800Z 19.6N 82.9W 45 KT 50 MPH 72H 08/0600Z 21.0N 81.0W 50 KT 60 MPH 96H 09/0600Z 23.5N 79.5W 50 KT 60 MPH 120H 10/0600Z 24.5N 81.5W 55 KT 65 MPH $$ Forecaster Pasch

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