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Tropical Storm Eta Forecast Discussion Number 44
2020-11-11 09:59:55| National Hurricane Center (Atlantic)
Issued at 400 AM EST Wed Nov 11 2020 000 WTNT44 KNHC 110859 TCDAT4 Tropical Storm Eta Discussion Number 44 NWS National Hurricane Center Miami FL AL292020 400 AM EST Wed Nov 11 2020 Eta has become better organized over the past few hours, with a better-defined eye feature on the Key West radar. Satellite pictures also show a more symmetric presentation and a large cluster of deep convection near the center. Radar data has shown increasing wind speeds in the mid-levels, which supports conservatively raising the initial wind speed to 60 kt. The current position is southwest of the eye feature on radar, assuming some shear remains, but a NOAA Hurricane Hunter aircraft is scheduled to be in the storm in a few hours to acquire better data on both the initial position and intensity. It appears that the center of Eta has re-formed to the north- northeast tonight, so an initial motion is hard to determine, but is estimated to be northward at about 10 kt. Remarkably, model guidance has become well clustered just east of the previous forecast track as it seems apparent that Eta will now recurve around the ridge toward the Florida Big Bend region and out into the western Atlantic Ocean. The biggest change is that the models are faster than before, and the official forecast follows that lead, along with a small eastward forecast adjustment, near or just east of the model consensus. Further strengthening is possible today while the shear remains low-to-moderate. However, all of the models do show increasing shear by tonight, and the NHC forecast continues to call for weakening of Eta as it approaches the west coast of Florida. However, it would take only a small forecast error to allow Eta to come ashore as a hurricane, and hence a Hurricane Watch has been issued this morning. Rapid weakening is anticipated once Eta makes landfall, and strong shear should prevent any regeneration over the western Atlantic Ocean. The new forecast is a little higher than the previous advisory, mostly due to current trends, and is closer to the more bullish HMON and HWRF models. Key Messages: 1. Life-threatening storm surge is possible early Thursday along portions of the Florida Gulf Coast from Bonita Beach to Steinhatchee River, including Tampa Bay and Charlotte Harbor. Residents in this area should follow any advice given by local officials. 2. Hurricane-force winds are possible along portions of the west coast of Florida from Anna Maria Island to Yankeetown by early Thursday. Tropical-storm-force winds are expected by late Wednesday along portions of the Florida Gulf Coast from Bonita Beach to Suwanee River, and are possible Thursday from Suwannee River to Aucilla River. Interests elsewhere along the Florida Gulf Coast should monitor the progress of Eta, as additional watches and warnings may be needed today. 3. Heavy rainfall from Eta will continue across western Cuba and South Florida and spread northward across portions of West and North Florida Wednesday through Friday. Additional flash and urban flooding will be possible in South Florida on Wednesday, especially across previously inundated areas, and across portions of West Florida through Friday. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 25.0N 84.1W 60 KT 70 MPH 12H 11/1800Z 26.4N 83.9W 65 KT 75 MPH 24H 12/0600Z 27.9N 83.4W 60 KT 70 MPH 36H 12/1800Z 29.2N 82.6W 45 KT 50 MPH...INLAND 48H 13/0600Z 30.2N 81.2W 30 KT 35 MPH 60H 13/1800Z 30.9N 79.5W 30 KT 35 MPH 72H 14/0600Z 31.0N 78.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 15/0600Z...DISSIPATED $$ Forecaster Blake
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Tropical Storm Theta Forecast Discussion Number 6
2020-11-11 09:55:57| National Hurricane Center (Atlantic)
Issued at 900 AM GMT Wed Nov 11 2020 000 WTNT45 KNHC 110855 TCDAT5 Tropical Storm Theta Discussion Number 6 NWS National Hurricane Center Miami FL AL302020 900 AM GMT Wed Nov 11 2020 Convection associated with Theta has decreased further this morning, with strong southwesterly shear displacing the remaining convection to the north of the center. Based on the decreased organization, the initial intensity is lowered slightly to 55 kt. Theta has continued to slow its forward speed, with the initial motion now 075/7. The cyclone is being steered by the southern part of the mid-latitude westerlies to the north of a mid-level ridge, and this general motion should continue for the next 72 h or so. After that time, the global models suggest that the cyclone should shear apart, with the remnant low-level circulation moving northeastward on the southeast side of a deep-layer cyclone over the northeastern Atlantic. There has been little change in the guidance since the previous advisory, and the new official forecast track is similar to the previous track. While the cyclone is currently experiencing strong shear, the global models show that this might diminish somewhat during the next 72 h as Theta moves into an area of light winds near an upper-level trough axis. This, combined with sufficient instability for deep convection, should allow the storm to change little in strength during this time. After 72 h, strong mid- to upper-level northerly flow should cause the system to weaken as the convection dissipates and the upper-level portion of the storm is pushed off to the south. The new intensity forecast is lowered a bit from the previous forecast, and it lies in the middle of the intensity guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 29.4N 34.7W 55 KT 65 MPH 12H 11/1800Z 29.9N 33.5W 55 KT 65 MPH 24H 12/0600Z 30.4N 31.5W 55 KT 65 MPH 36H 12/1800Z 30.8N 29.1W 50 KT 60 MPH 48H 13/0600Z 31.3N 26.7W 50 KT 60 MPH 60H 13/1800Z 31.8N 24.4W 50 KT 60 MPH 72H 14/0600Z 32.1N 23.1W 50 KT 60 MPH 96H 15/0600Z 32.5N 21.5W 45 KT 50 MPH 120H 16/0600Z 34.0N 20.0W 35 KT 40 MPH...POST-TROPICAL $$ Forecaster Beven
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Tropical Storm Eta Forecast Discussion Number 43
2020-11-11 03:54:53| National Hurricane Center (Atlantic)
Issued at 1000 PM EST Tue Nov 10 2020 000 WTNT44 KNHC 110254 TCDAT4 Tropical Storm Eta Discussion Number 43 NWS National Hurricane Center Miami FL AL292020 1000 PM EST Tue Nov 10 2020 Eta has been maintaining a large cluster of deep convection over the northeastern portion of its circulation this evening. NWS Doppler radar data from Key West is showing a well-defined mid-level circulation in that area, but NOAA reconnaissance aircraft data so far still indicates that the low-level center is located near the southwestern portion of the convective mass. However, it is possible that the center will re-form closer to the mid-level center overnight. The plane has measured peak 850-mb flight-level winds of 67 kt, and SFMR winds of 52 kt. Based on these data the initial intensity has been raised to 55 kt. Eta's initial motion is a somewhat uncertain 015/8 kt. There has once again been a significant eastward shift in the 18Z dynamical model guidance, with the GFS, HWRF, and UKMET models all showing a faster north-northeastward motion toward the Florida west coast. As a result, the NHC forecast has again been shifted eastward and lies near the TVCA multi-model consensus through 36 h. After that time, the NHC track is slower and west of the bulk of the consensus aids as the ECMWF still shows Eta weakening and lingering near the Florida Big Bend. While the new track has been shifted significantly eastward after 36 h or so, some continuity with the previous forecast is maintained with a slower northward motion between the two model camps. While there is increasing confidence in the faster north-northeastward motion in the short-term, there is still considerable uncertainty by 48 hours and beyond, and further adjustments to the track forecast could be required overnight. Some additional strengthening is likely overnight and Wednesday while Eta remains over warm water and within an area of low-to-moderate vertical wind shear. If the center re-forms closer to the deep convection, Eta could re-gain hurricane status within the next 12-24 hours. After that time, increasing southwesterly shear and cooler SSTs are likely to result in some weakening. The updated NHC intensity forecast is close to the SHIPS and HCCA model guidance. Given the eastward shift in the track and the expected faster motion of Eta, a Tropical Storm Warning and Storm Surge Watch are being issued for a portion of the west coast of Florida. Additional warnings could be required early Wednesday. Key Messages: 1. Life-threatening storm surge is possible Thursday along portions of the Florida Gulf Coast from Bonita Beach to Steinhatchee River, including Tampa Bay and Charlotte Harbor. Residents in this area should follow any advice given by local officials. 2. Tropical-storm-force winds are expected by late Wednesday along portions of the Florida Gulf Coast from Bonita Beach to Suwanee River, and are possible Thursday from Suwannee River to Aucilla River. Interests elsewhere along the Florida Gulf Coast should monitor the progress of Eta, as additional watches and warnings may be needed overnight. 3. Heavy rainfall from Eta will continue across western Cuba and south Florida through tonight, and spread northward across portions of west Florida, the eastern Florida Panhandle, and north Florida Wednesday through Friday. Additional flash and urban flooding is possible in south Florida tonight, especially across previously inundated areas, and eventually across portions of west Florida, the eastern Florida Panhandle, and north Florida Wednesday through Friday. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 23.8N 84.5W 55 KT 65 MPH 12H 11/1200Z 25.0N 84.3W 60 KT 70 MPH 24H 12/0000Z 26.5N 84.0W 60 KT 70 MPH 36H 12/1200Z 27.7N 83.7W 55 KT 65 MPH 48H 13/0000Z 28.8N 83.1W 45 KT 50 MPH 60H 13/1200Z 29.7N 82.5W 35 KT 40 MPH...INLAND 72H 14/0000Z 30.3N 82.3W 30 KT 35 MPH...INLAND 96H 15/0000Z 30.8N 82.3W 30 KT 35 MPH...INLAND 120H 16/0000Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Theta Forecast Discussion Number 5
2020-11-11 03:47:52| National Hurricane Center (Atlantic)
Issued at 300 AM GMT Wed Nov 11 2020 000 WTNT45 KNHC 110247 TCDAT5 Tropical Storm Theta Discussion Number 5 NWS National Hurricane Center Miami FL AL302020 300 AM GMT Wed Nov 11 2020 Convection with Theta has waned some since the previous advisory, with the coldest cloud tops now focused in a band on the northeastern side of the partially exposed circulation. Despite this decrease in convective coverage, a 2304 UTC ASCAT-B pass showed a large region of 50 kt winds with at least one 55 kt barb. Accounting for a bit of undersampling of this instrument and maintaining continuity with the previous advisory, the maximum sustained winds have been kept at 60 kt for this advisory. Theta has slowed a bit tonight on the same east-northeast heading at 075/10 kt. The steering philosophy in the first part of the forecast has remained the same, with Theta moving off to the east-northeast while it continues to round the northern edge of a mid-level ridge providing the steering flow. The latest track guidance has slowed down the forward motion a bit more this cycle, and the new track forecast splits the difference between the previous forecast and some of the more reliable global model guidance that is slower and south of the NHC track. At the end of the forecast period both the ECMWF and GFS are forecasting Theta to become a shallow vortex as the remaining convection is stripped away, and this could cause Theta to slow down in the weaker low-level flow and move more slowly to the northeast at the end of the forecast period. Despite moving over gradually decreasing sea surface temperatures over the next 48-72 h, upper-level temperatures are also forecast to cool per GFS-SHIPS, which should provide enough instability for moderate to deep convection. In addition, vertical wind shear may decrease some in the 48-72 h period as Theta remains in light flow along an upper-level trough axis. Therefore, the latest NHC intensity forecast remains on the high end of the guidance for the first three days, but now shows a faster weakening trend thereafter as vertical wind shear increases out of the north and strips the remaining convection away. At 5 days the forecast now makes Theta a remnant low since it appears the circulation will be too shallow to take advantage of more favorable baroclinic conditions that would ordinarily allow for extratropical transition. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 29.4N 35.5W 60 KT 70 MPH 12H 11/1200Z 29.7N 34.2W 60 KT 70 MPH 24H 12/0000Z 30.1N 32.5W 55 KT 65 MPH 36H 12/1200Z 30.5N 30.4W 55 KT 65 MPH 48H 13/0000Z 31.0N 27.7W 55 KT 65 MPH 60H 13/1200Z 31.7N 25.2W 55 KT 65 MPH 72H 14/0000Z 32.2N 23.2W 55 KT 65 MPH 96H 15/0000Z 32.8N 21.4W 50 KT 60 MPH 120H 16/0000Z 34.5N 20.1W 40 KT 45 MPH...POST-TROP/REMNT LOW $$ Forecaster Papin/Brown
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Tropical Storm Eta Forecast Discussion Number 42
2020-11-10 21:52:49| National Hurricane Center (Atlantic)
Issued at 300 PM CST Tue Nov 10 2020 000 WTNT44 KNHC 102052 TCDAT4 Tropical Storm Eta Discussion Number 42 NWS National Hurricane Center Miami FL AL292020 300 PM CST Tue Nov 10 2020 Eta's convective structure has changed little since the previous advisory. A CDO-like feature with cloud tops colder than -70C has persisted, with some overshooting tops of -80C to -85C located east and southeast of the center. Recent passive microwave satellite data indicates that Eta is still sheared from the northwest, with an intermittent mid-level eye feature showing up. Satellite classifications have essentially remained unchanged, with SAB reporting 45-55 kt and TAFB reporting 55 kt. The initial intensity remains at 50 kt based on a blend of these satellite classifications and a UW-CIMSS SATCON estimates of 45-48 kt. The initial motion estimate is now northward, or 360/06 kt. The biggest surprise is the large eastward shift in all of the NHC model guidance, which was possibly due at least in part to all of the dropsondes that the NOAA G-IV jet aircraft dropped around Eta earlier this morning, All of the guidance is now in good agreement on a broad, deep-layer trough moving eastward across the south-central and southeastern United States, which will erode the subtropical ridge to the north of Eta that has been impeding Eta's poleward progress he past couple of days. This generally northward to northeastward steering pattern is expected to persist through the entire 120-h forecast period, with only slight shifts east or west of he current forecast track due to how vertically deep Eta remains when it reaches the northeastern Gulf of Mexico and Apalachee Bay in a few days. The current forecast track maintains Eta as at least a moderate tropical cyclone through the period, with only a slight bend back toward the northwest when the system is expected to interact with an approaching frontal system. The new NHC track forecast has been shifted about 150 n mi east of the previous advisory track at 96 and 120 hours, and further eastward shifts in the track may be required, closer to the consensus models TCVA/TVCN and NOAA-HCCA. Eta is forecast to remain in a low-to-moderate vertical wind shear environment and over SSTs of at least 27 deg C for the next 36 hours or so. Intermittent entrainment of dry mid-level air should prevent any rapid strengthening from occurring, but Eta could still become a hurricane between in 24 to 36 h before more significant shear begins to affect the cyclone. By day 3 and beyond, increasing northwesterly vertical wind shear combined with cooler SSTs should cause Eta to weaken. The new intensity forecast is essentially the same as the previous advisory, and is a little below the consensus models IVCN, HCCA, and FSSE, all of which make Eta a hurricane again by 36 hours. Due to the expected northwesterly shear after 36 hours, the 34-kt wind radii were expanded in the eastern semicircle, which is the side of the cyclone where most of the deep convection and associated stronger winds will be located. Given this and the eastward adjustment to the track forecast, a Tropical Storm Watch has been issued for portions of the Florida west coast, and a Tropical Storm Warning is in effect for the Dry Tortugas. Key Messages: 1. Tropical-storm-force winds are possible along portions of the Florida Gulf Coast by Thursday afternoon, and a Tropical Storm Watch has been issued. Interests elsewhere along the Florida Gulf Coast should monitor the progress of Eta, as additional watches may be needed tonight. 2. Heavy rainfall from Eta will continue across western Cuba and South Florida today and tonight, then potentially spread up the west coast of the Florida Peninsula Wednesday through Thursday. Additional flash and urban flooding will be possible in South Florida, especially across previously inundated areas, and eventually along portions of West Florida and the Sun Coast. Flash and urban flooding will also be possible for western Cuba. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 23.2N 85.1W 50 KT 60 MPH 12H 11/0600Z 24.1N 84.9W 55 KT 65 MPH 24H 11/1800Z 25.6N 84.8W 60 KT 70 MPH 36H 12/0600Z 26.9N 84.5W 60 KT 70 MPH 48H 12/1800Z 27.9N 84.2W 55 KT 65 MPH 60H 13/0600Z 28.7N 84.0W 45 KT 50 MPH 72H 13/1800Z 29.1N 84.0W 40 KT 45 MPH 96H 14/1800Z 29.7N 84.6W 35 KT 40 MPH 120H 15/1800Z 30.7N 84.9W 30 KT 35 MPH...INLAND $$ Forecaster Stewart
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