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Tropical Storm Eta Forecast Discussion Number 3

2020-11-01 09:48:57| National Hurricane Center (Atlantic)

Issued at 400 AM EST Sun Nov 01 2020 000 WTNT44 KNHC 010848 TCDAT4 Tropical Storm Eta Discussion Number 3 NWS National Hurricane Center Miami FL AL292020 400 AM EST Sun Nov 01 2020 Eta has not become appreciably better organized over the past few hours. A large convective band is evident well to the east and northeast of the estimated center, but this band does not have much curvature at this time. A small burst of deep convection is occurring near or over the center, which is likely the early stages of the development of a Central Dense Overcast. Currently, there is a significant amount of lightning in the outer band but little lightning near the center. The intensity is held at 35 kt for this advisory, in agreement with Dvorak estimates from TAFB and SAB. Eta will be moving over very warm waters of SSTs above 29 deg C and in an environment of fairly light vertical shear. Therefore, strengthening is likely. The official forecast, like the previous ones, calls for the cyclone to become a hurricane before approaching Central America. There is also a possibility of rapid strengthening, as suggested by the SHIPS Rapid Intensification Index. The NHC intensity forecast is very similar to the latest corrected consensus prediction up to the expected landfall and follows the Decay-SHIPS guidance after that point. The center location is somewhat uncertain, and my best estimate of initial motion is about the same as before, or 275/13 kt. The track forecast reasoning has not changed significantly. A mid-level ridge to the north and northwest of Eta should cause a westward or west-southwestward motion for the next few days. This would take the cyclone inland over Central America in 72 hours or so. The official track forecast is similar to the previous one, and lies near the simple model consensus and a little north of the corrected consensus. Key Messages: 1. Eta is expected to strengthen to a hurricane early next week as it approaches the coast of Central America early Tuesday, and there is a risk of storm surge, hurricane-force winds, and heavy rainfall for portions of Nicaragua and Honduras, where Hurricane Watches have been issued. Hurricane warnings could be needed for portions of those areas later today. 2. Through Thursday afternoon, heavy rainfall from Eta may lead to life-threatening flash flooding and river flooding, along with landslides in areas of higher terrain across portions of Jamaica, the Cayman Islands, the southern coast of Hispaniola, northern Honduras and northern Nicaragua. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 15.2N 75.7W 35 KT 40 MPH 12H 01/1800Z 15.3N 77.7W 45 KT 50 MPH 24H 02/0600Z 15.3N 79.7W 55 KT 65 MPH 36H 02/1800Z 15.1N 81.2W 65 KT 75 MPH 48H 03/0600Z 14.7N 82.2W 75 KT 85 MPH 60H 03/1800Z 14.4N 83.0W 80 KT 90 MPH 72H 04/0600Z 14.2N 83.7W 60 KT 70 MPH...INLAND 96H 05/0600Z 14.3N 85.7W 30 KT 35 MPH...INLAND 120H 06/0600Z 15.0N 87.5W 25 KT 30 MPH...INLAND $$ Forecaster Pasch

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Tropical Storm Eta Forecast Discussion Number 2

2020-11-01 03:47:56| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Oct 31 2020 000 WTNT44 KNHC 010247 TCDAT4 Tropical Storm Eta Discussion Number 2 NWS National Hurricane Center Miami FL AL292020 1100 PM EDT Sat Oct 31 2020 Satellite imagery indicates that shower activity associated with the cyclone continues to become better organized, with a convective band wrapping about halfway around the center. Satellite intensity estimates from TAFB and SAB have increased to 35 kt, and the CIMSS satellite consensus is near 40 kt. Based on these data, the depression is upgraded to Tropical Storm Eta, the twenty-eighth named storm of the 2020 season. This ties the record for storms set in the 2005 season and is the first time the name Eta has been used in the Atlantic basin. The initial motion is 275/13. A low- to mid-level ridge axis that extends from the subtropical Atlantic southwestward to Cuba and the Bahamas is currently the main steering influence, and the model guidance is in good agreement that this feature should cause the storm to move westward for the next 24-36 h. Between 36-72 h, a building low- to mid-level ridge over the Gulf of Mexico should cause Eta to turn west-southwestward as it approaches the coasts of Nicaragua and Honduras. Beyond that time, there remains significant spread in the models, with the GFS showing a slow motion toward the northwest near the coast of Honduras while the ECMWF/UKMET show a continued west-southwestward motion into the Pacific. Given the spread, the NHC official track forecast shows a slow motion on days 3 through 5, and brings the cyclone's center slowly across portions of Nicaragua and Honduras. The new forecast track is close to the multi-model consensus, and the 72-120 h part remains low confidence. Eta is over warm water and is in environment of light vertical wind shear. These conditions are expected to continue until the system nears the coast of Central America on 60-72 h. Thus, steady to possibly rapid strengthening is expected, with the storm forecast to reach hurricane strength between 36-48 h. The intensity guidance has trended stronger since the last advisory, and this part of the new intensity forecast is now a little below the intensity consensus. After 72 h, the intensity forecast is tied to whether or not the cyclone's center moves inland over Central America, and the current forecast is based on the forecast track that takes the center well inland. Key Messages: 1. The depression is expected to strengthen to a hurricane early next week as it approaches the coast of Central America late Monday and Monday night, and there is a risk of storm surge, hurricane-force winds, and heavy rainfall for portions of Nicaragua and Honduras where Hurricane Watches have been issued. Hurricane warnings could be needed for portions of those areas on Sunday. 2. Through Thursday evening, heavy rainfall from Eta may lead to flash flooding and river flooding across portions of Jamaica, the Cayman Islands, and Central America, which could lead to landslides in areas of higher terrain. Flooding is also possible near the southern coast of Hispaniola, depending upon the track of the storm. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 15.0N 74.2W 35 KT 40 MPH 12H 01/1200Z 15.1N 76.4W 40 KT 45 MPH 24H 02/0000Z 15.3N 78.8W 50 KT 60 MPH 36H 02/1200Z 15.2N 80.8W 60 KT 70 MPH 48H 03/0000Z 14.7N 82.1W 70 KT 80 MPH 60H 03/1200Z 14.2N 82.8W 80 KT 90 MPH 72H 04/0000Z 13.7N 83.7W 70 KT 80 MPH...INLAND 96H 05/0000Z 14.0N 85.5W 35 KT 40 MPH...INLAND 120H 06/0000Z 14.5N 87.0W 25 KT 30 MPH...INLAND $$ Forecaster Beven

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Post-Tropical Cyclone Zeta Forecast Discussion Number 21

2020-10-29 21:37:21| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Thu Oct 29 2020 000 WTNT43 KNHC 292037 TCDAT3 Post-Tropical Cyclone Zeta Discussion Number 21 NWS National Hurricane Center Miami FL AL282020 500 PM EDT Thu Oct 29 2020 Zeta lost tropical characteristics and was declared post-tropical a few hours ago. The surface pressure field has become elongated with the center now embedded within a frontal zone over the Mid-Atlantic states. The maximum sustained winds are still estimated to be 45 kt, based on an observation received from northeastern North Carolina a few hours ago, and winds have been increasing at marine sites located just off the Mid-Atlantic coast. Zeta is zooming toward the east-northeast (060/48 kt), and its center is just about to move off the Delmarva Peninsula over the western Atlantic waters. This motion should continue for the next day or so since Zeta is embedded within fast westerly flow ahead of a strong mid-level trough. Some baroclinic re-intensification is expected over the next day or so while Zeta moves farther out over the western Atlantic, and the 12-hour forecast intensity is based on the GFS and ECMWF global models. Zeta's center is expected to dissipate within the frontal zone by 24 hours, with another strong low pressure area likely to develop and move toward the north Atlantic over the next several days. The forecast wind radii are based on guidance from the Ocean Prediction Center. This is the last advisory issued on Zeta. Additional information on this system can be found in High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php KEY MESSAGES: 1. Strong wind gusts are still possible over portions of extreme eastern North Carolina, southeastern Virginia, and the southern Delmarva Peninsula during the next couple of hours. 2. Through this evening, the last of the heavy rainfall along the track of Zeta is expected over the Mid-Atlantic. This rainfall may lead to flash, urban, small stream, and isolated minor river flooding. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 38.8N 75.3W 45 KT 50 MPH...POST-TROP/EXTRATROP 12H 30/0600Z 41.0N 66.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 30/1800Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Zeta Forecast Discussion Number 20

2020-10-29 15:52:44| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Thu Oct 29 2020 000 WTNT43 KNHC 291452 TCDAT3 Tropical Storm Zeta Discussion Number 20 NWS National Hurricane Center Miami FL AL282020 1100 AM EDT Thu Oct 29 2020 Zeta continues to move rapidly over land, and its maximum sustained winds are estimated to be near 45 kt over the southeastern quadrant, with thew highest winds occuring over elevated locations. The wind gust factor continues to be higher than usual due to the interaction with land. Zeta continues to accelerate northeastward and is now moving near 055/42 kt. The cyclone should accelerate some more ahead of a strong 500-mb trough moving into the eastern United States over the next day or so. The official track forecast is in reasonable agreement with the global model predictions. The pressure pattern of Zeta is becoming distorted, and starting to take on an extratropical appearance as the cyclone begins to interact with a nearby frontal system. By this afternoon, the global models indicate that the system will become a frontal low and thus extratropical. Some short-term baroclinic strengthening is possible over the western Atlantic, but the guidance suggests that the system will become absorbed into the frontal zone in 36 hours or so. KEY MESSAGES: 1. Strong, damaging wind gusts, which could cause tree damage and power outages, will continue to spread eastward across portions of the Carolinas and southeastern Virginia through this afternoon due to Zeta's fast forward speed. 2. Through today, heavy rainfall is expected near and in advance of Zeta from portions of the Ohio Valley, into the central Appalachians and Mid-Atlantic. This rainfall may lead to flash, urban, small stream, and isolated minor river flooding. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 36.5N 81.5W 45 KT 50 MPH...INLAND 12H 30/0000Z 39.4N 73.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 24H 30/1200Z 42.0N 60.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 31/0000Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Zeta Forecast Discussion Number 19

2020-10-29 09:40:14| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Thu Oct 29 2020 000 WTNT43 KNHC 290840 TCDAT3 Tropical Storm Zeta Discussion Number 19 NWS National Hurricane Center Miami FL AL282020 400 AM CDT Thu Oct 29 2020 Surface observations and Doppler radar data indicate that Zeta weakened to a tropical storm around 0600 UTC when it was located over central Alabama. During the past few hours, the cyclone's structure has degraded further with the center no longer easily apparent in radar images and convection appearing more ragged and asymmetric. The initial intensity is lowered to 50 kt for this advisory, and that could be a little generous. The minimum pressure is estimated to be 988 mb based on surface observations. The storm continues to accelerate, and the latest initial motion is northeastward at 34 kt. Zeta is expected to race northeastward today in the fast steering flow between a potent mid- to upper-level low to its west and a high pressure ridge to its southeast. This pattern should take the cyclone across the southeast and Mid-Atlantic states throughout the day, before emerging over the western Atlantic this evening. An even faster east-northeastward motion is predicted tonight and on Friday until the cyclone dissipates by Friday night. The tropical storm is forecast to weaken a little more during the next several hours as it remains over land, and Zeta will likely become extratropical by the time it reaches the mid-Atlantic states this afternoon. However, after that time, the models show the cyclone leveling off in strength or perhaps even re-intensifying over the western Atlantic before it becomes absorbed into a frontal zone in 36 to 48 hours. The NHC intensity forecast follows the GFS and ECMWF models. KEY MESSAGES: 1. Strong, damaging wind gusts, which could cause tree damage and power outages, will continue to spread well inland across portions of northeastern Alabama, northern Georgia, the Carolinas, and southeastern Virginia today due to Zeta's fast forward speed. Wind gusts could be especially severe across the southern Appalachian Mountains. 2. Through today, heavy rainfall is expected near and in advance of Zeta from portions of the central Appalachians, Mid-Atlantic and lower to middle Ohio Valley. This rainfall may lead to flash, urban, small stream, and isolated minor river flooding. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 34.0N 85.5W 50 KT 60 MPH...INLAND 12H 29/1800Z 37.7N 79.1W 45 KT 50 MPH...POST-TROP/EXTRATROP 24H 30/0600Z 40.8N 66.9W 50 KT 60 MPH...POST-TROP/EXTRATROP 36H 30/1800Z 43.4N 54.6W 50 KT 60 MPH...POST-TROP/EXTRATROP 48H 31/0600Z...DISSIPATED $$ Forecaster Cangialosi

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