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Tropical Storm Zeta Forecast Discussion Number 4

2020-10-25 15:58:11| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun Oct 25 2020 000 WTNT43 KNHC 251457 TCDAT3 Tropical Storm Zeta Discussion Number 4 NWS National Hurricane Center Miami FL AL282020 1100 AM EDT Sun Oct 25 2020 Although the cloud pattern of the storm is not well-organized and somewhat elongated zonally, the system is producing very vigorous deep convection, particularly over the southern portion of the circulation. Cirrus cloud motions show that the upper-level outflow is well-defined. The current intensity estimate remains at 35 kt in agreement with Dvorak values from both TAFB and SAB, and pending another Hurricane Hunter mission into the system this afternoon. The center is difficult to locate at this time, and the best estimate for motion is quasi-stationary. A high pressure area developing near Florida should induce a general northwestward motion over the next couple of days. Later, a shortwave trough approaching from the west is likely to cause Zeta to turn northward and north-northeastward while it nears the northern Gulf Coast in 72-84 hours. The official track forecast lies between the GFS solution which is farther east and the ECMWF prediction which lies farther south and west. Given the favorable upper-level outflow pattern and very high oceanic heat content over the northwestern Caribbean, strengthening is likely until the center moves near or over the Yucatan Peninsula late tomorrow. Zeta should be near or at hurricane strength when it approaches the Yucatan. The official intensity forecast for the next 36 hours is close to the model consensus. After Zeta moves into the central Gulf of Mexico, increasing southwesterly shear and diminishing oceanic heat content are expected to prevent strengthening. The NHC intensity forecast over the Gulf is above the latest model consensus. Although not explicitly shown in the official forecast, the unfavorable atmospheric and oceanic conditions over the northern Gulf of Mexico could cause Zeta to weaken by the time the center nears the northern Gulf coast. However, users are reminded that these intensity forecasts are subject to uncertainty. KEY MESSAGES: 1. Tropical storm conditions are expected in portions of the northern Yucatan Peninsula of Mexico Monday night and early Tuesday, with hurricane conditions possible. Tropical storm conditions could occur over extreme western Cuba on Monday. 2. Through Wednesday, heavy rainfall is expected from Zeta across portions of central and western Cuba, the Cayman Islands, Jamaica, the northeast Yucatan peninsula of Mexico, southern Florida and the Keys. This rainfall may lead to flash flooding in urban areas. 3. Zeta could be at or just below hurricane strength when it approaches the northern Gulf Coast on Wednesday, and could bring storm surge, rainfall, and wind impacts to areas from Louisiana to the Florida Panhandle. Residents in these areas should monitor the progress of Zeta and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 17.8N 83.8W 35 KT 40 MPH 12H 26/0000Z 18.4N 84.1W 40 KT 45 MPH 24H 26/1200Z 19.2N 85.1W 50 KT 60 MPH 36H 27/0000Z 20.3N 86.7W 60 KT 70 MPH 48H 27/1200Z 21.9N 88.7W 65 KT 75 MPH 60H 28/0000Z 24.0N 90.3W 65 KT 75 MPH 72H 28/1200Z 27.0N 90.5W 65 KT 75 MPH 96H 29/1200Z 35.0N 85.5W 25 KT 30 MPH...INLAND 120H 30/1200Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Zeta Forecast Discussion Number 3

2020-10-25 10:01:08| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sun Oct 25 2020 000 WTNT43 KNHC 250900 TCDAT3 Tropical Storm Zeta Discussion Number 3 NWS National Hurricane Center Miami FL AL282020 500 AM EDT Sun Oct 25 2020 Earlier this morning, the tropical cyclone located over the northwestern Caribbean Sea was upgraded to Tropical Storm Zeta at 0600 UTC based on 0314Z ASCAT surface wind data of 32-33 kt located southeast of the broad center. Since then, a NOAA reconnaissance aircraft has been investigating Zeta and has found maximum 925-mb flight-level winds of about 40 kt and reliable SFMR surface winds of 33-36 kt. Recent satellite classifications from TAFB, SAB, and UW-CIMSS are 35 kt. Based on these data, the initial intensity is set at 35 kt. The initial motion estimate is stationary. Although Zeta has been steadily losing latitude during the past 12 hours, this has been primarily due to the broad low-level center reforming closer to the very intense convection located in the southern semicircle of the cyclone's large circulation. Satellite trends over the past 6 hours indicate that a mid-level circulation located about 90 nmi east of the low-level center is likely imparting a weak southerly component of motion on Zeta as well. Over the course of the next 72 hours, a weak shortwave trough currently located over the southeastern U.S. from the Tennessee Valley southward into the north-central Gulf of Mexico will continue to move eastward, allowing a low- to mid-level ridge to steadily build westward across the Bahamas, Florida, and the central Gulf of Mexico. This will gradually force Zeta on a northwestward track across or near the northeastern tip of the Yucatan Peninsula in about 48 h and into the central Gulf of Mexico by 72 h. The latest NHC model guidance is in very agreement on this developing 3-day track scenario. Thereafter, however, the models diverge fairly significantly due to uncertainty in the evolution of the next steering mechanism -- a trough over the northwestern U.S. that will dig southward and phase up/merge with a trough off the southern California and Baja California coasts. Phasing of northern and southern stream systems is always difficult to forecast, especially when one of those systems is outside the U.S. upper-air observing system like the system currently is off southern California. After the two systems phase in about 48 hours, a powerful mid/upper-level low is forecast to form by 72 h and eject eastward out of the southwestern U.S., causing the ridge over the Gulf of Mexico to erode eastward. This will allow Zeta to turn northward and then northeastward toward the north-central Gulf coast. The global models remain in poor agreement on the details of the timing of the eastward movement of the upper-low, resulting in model solutions ranging from Louisiana (ECMWF-UKMET-FSSE) to the Florida Panhandle (HWRF-HMON). The new NHC track forecast is a little left of the previous advisory track through 72 hours, and lies near the middle of the guidance envelope, close to the HCCA and TVCA multi-model consensus. However, given the current lack of motion of the system and the large model spread late in the period, the details of the track forecast are more uncertain than usual. Although the low- and mid-level circulations remain unaligned, the overall environment for the next 60-72 hours is expected to remain conducive for at least gradual intensification. After 72 hours, however, the deep-layer vertical wind shear is expected to increase while Zeta moves over cooler SSTs near the northern Gulf Coast, which should result in weakening before the cyclone moves inland. The new NHC intensity forecast is a tad higher than the previous advisory, and lies near the upper end of the intensity guidance. While the current NHC forecast indicates that the system should weaken below hurricane strength before landfall, users are reminded that strong tropical storms can still produce significant storm surge, rainfall, and wind impacts along the northern Gulf Coast. The cyclone should be absorbed into a frontal system by the end of the forecast period. KEY MESSAGES: 1. Zeta is expected to produce tropical storm conditions over extreme western Cuba on Monday. Tropical storm conditions are possible in the northern Yucatan Peninsula of Mexico Monday night and early Tuesday. 2. Through Wednesday, heavy rainfall is expected from Tropical Storm Zeta across portions of central and western Cuba, the Cayman Islands, Jamaica, the northeast Yucatan peninsula of Mexico, Southern Florida and the Keys. This rainfall may lead to flash flooding in urban areas. 3. Zeta is forecast to approach the northern Gulf Coast as a tropical storm Tuesday night and Wednesday, and could bring storm surge, rainfall, and wind impacts to areas from Louisiana to the Florida Panhandle. Residents in these areas should monitor the progress of Zeta and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 17.7N 83.5W 35 KT 40 MPH 12H 25/1800Z 18.2N 83.8W 40 KT 45 MPH 24H 26/0600Z 18.9N 84.4W 45 KT 50 MPH 36H 26/1800Z 19.8N 85.7W 55 KT 65 MPH 48H 27/0600Z 21.1N 87.4W 65 KT 75 MPH 60H 27/1800Z 22.9N 89.5W 70 KT 80 MPH 72H 28/0600Z 25.4N 90.7W 65 KT 75 MPH 96H 29/0600Z 32.0N 89.1W 35 KT 40 MPH...INLAND 120H 30/0600Z...DISSIPATED $$ Forecaster Stewart

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Hurricane Epsilon Forecast Discussion Number 26

2020-10-25 09:37:04| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Oct 25 2020 000 WTNT42 KNHC 250836 TCDAT2 Hurricane Epsilon Discussion Number 26 NWS National Hurricane Center Miami FL AL272020 500 AM AST Sun Oct 25 2020 Although the cloud pattern of Epsilon is beginning to expand over the northwestern portion of the circulation as the hurricane begins its extratropical transition, the storm continues to produce inner-core convection. Recent shortwave infrared satellite imagery suggest that there is some northeast-to-southwest tilt between the mid- and low-level centers. Since there has been little overall change in the inner-core structure since the previous advisory, the initial intensity is held at 65 kt in agreement with the earlier ASCAT data. Epsilon is moving north of the north wall of the Gulf Stream and will be over much colder SSTs later this morning. This, along with an approaching baroclinic zone, should cause Epsilon to quickly lose its tropical characteristics and become an extratropical low by later today. The post-tropical cyclone is expected to remain a large and powerful cyclone over the north Atlantic during the next day or so. The global models indicate that the post-tropical cyclone will be absorbed by a large extratropical low over the north Atlantic within 48 hours. The hurricane continues to accelerate northeastward, with an initial motion estimate of 050/26 kt. A continued northeastward acceleration is expected through tonight, and rather faster northeastward motion is forecast until the post-tropical cyclone is absorbed by the larger extratropical low Monday night. The track guidance remains tightly clustered and the new NHC forecast track is essentially an update of the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 42.8N 53.7W 65 KT 75 MPH 12H 25/1800Z 45.5N 47.3W 60 KT 70 MPH...POST-TROP/EXTRATROP 24H 26/0600Z 49.7N 36.2W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 26/1800Z 54.7N 26.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 48H 27/0600Z...ABSORBED BY AN EXTRATROPICAL LOW $$ Forecaster Brown

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Tropical Depression Twenty-Eight Forecast Discussion Number 2

2020-10-25 03:49:25| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sat Oct 24 2020 774 WTNT43 KNHC 250248 CCA TCDAT3 Tropical Depression Twenty-Eight Discussion Number 2...Corrected NWS National Hurricane Center Miami FL AL282020 1100 PM EDT Sat Oct 24 2020 Corrected timing in Key Message number 3 Deep convection has increased during the past few hours south of the estimated low-level position based on aircraft data from just after the release of the previous advisory. In fact, geostationary imagery suggests that the low-level center could be trying to reform closer to the deep convection. The initial intensity is set to 30 kt based on the latest Dvorak estimate from SAB. Another NOAA Hurricane Hunter aircraft will investigate the system overnight and provide additional data on the cyclone's structure and intensity. As noted above, the depression hasn't moved much, and the system currently appears to be stationary. Satellite imagery and upper-air data show a shortwave trough moving through the southeastern United States, which has weakened the steering flow around the cyclone. As the shortwave moves eastward, the subtropical ridge will expand westward to the north of the tropical cyclone by Monday, which should result in a steadier west-northeastward motion. After that time, a powerful mid/upper-level low is forecast to eject out of the southwestern U.S., which will weaken the ridge and cause the tropical cyclone to turn northward and northeastward as it approaches the northern Gulf Coast. The global models are not in good agreement on the details of the timing of the eastward movement of the upper-low. While this isn't unusual, it results in significant differences in when and where the tropical cyclone turns and exactly where it crosses the Gulf Coast next week, with model solutions ranging from Louisiana to the Florida Panhandle. The new NHC track forecast lies near the middle of the guidance envelope between the HCCA and the TVCA multi-model consensus. However, given the current lack of motion of the system and the large model spread late in the period, the details of the track forecast are more uncertain than usual. If the cyclone's low- and mid-level circulations can become better aligned, the environment for the next 2 to 3 days appears conducive for steady intensification, with low shear and SSTs of near 30C in the northwestern Caribbean and above 28C in the southern Gulf. After 72 hours, the shear is expected to increase while the cyclone moves over cooler SSTs near the northern Gulf Coast, which should result in weakening before the center moves inland. The new NHC intensity forecast is a bit higher than the previous one through about 60 hours, and is a blend of the latest intensity consensus aids and HCCA. While the current NHC forecast indicates that the system should weaken below hurricane strength before landfall, users are reminded that strong tropical storms can still produce significant storm surge, rainfall, and wind impacts along the northern Gulf Coast. The cyclone should be absorbed into a frontal system by the end of the forecast period. KEY MESSAGES: 1. The depression is forecast to strengthen to a tropical storm by Sunday and tropical storm conditions are expected in extreme western Cuba on Monday. Tropical storm conditions are possible in the northern Yucatan Peninsula of Mexico Monday night and early Tuesday. 2. Through Wednesday, heavy rainfall is expected across portions of central and western Cuba, the Cayman Islands, Jamaica, the northeast Yucatan peninsula of Mexico, southern Florida and the Florida Keys. This rainfall may lead to flash flooding in urban areas. 3. The system is forecast to approach the northern Gulf Coast as a tropical storm Tuesday night and Wednesday, and could bring storm surge, rainfall, and wind impacts to areas from Louisiana to the Florida Panhandle. Residents in these areas should monitor the progress of the depression and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 18.9N 83.1W 30 KT 35 MPH 12H 25/1200Z 19.2N 83.3W 35 KT 40 MPH 24H 26/0000Z 20.0N 83.7W 40 KT 45 MPH 36H 26/1200Z 20.7N 84.9W 50 KT 60 MPH 48H 27/0000Z 21.7N 86.6W 55 KT 65 MPH 60H 27/1200Z 23.2N 88.6W 65 KT 75 MPH 72H 28/0000Z 25.4N 90.3W 65 KT 75 MPH 96H 29/0000Z 31.5N 89.5W 40 KT 45 MPH...INLAND 120H 30/0000Z...ABSORBED $$ Forecaster Brennan

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Hurricane Epsilon Forecast Discussion Number 25

2020-10-25 03:34:31| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Oct 24 2020 000 WTNT42 KNHC 250234 TCDAT2 Hurricane Epsilon Discussion Number 25 NWS National Hurricane Center Miami FL AL272020 1100 PM AST Sat Oct 24 2020 Epsilon has become a little less organized during the past couple of hours. The hurricane is still producing inner-core convection, but cloud tops have gradually warmed, and the overall cloud pattern has become asymmetric once again. ASCAT-A data from just after 00Z showed maximum winds of 55-60 kt southeast of Epsilon's center. The intensity of the hurricane is therefore set at 65 kt, assuming a little undersampling from the ASCAT instrument. The wind radii analysis was also updated based on the ASCAT data. The hurricane is currently located over relatively warm waters associated with the Gulf Stream. Epsilon is forecast to remain over the Gulf Stream for at least another 12 hours, and should maintain its tropical structure during that time. The cyclone is forecast to move over much cooler water by Sunday afternoon and this should cause it to quickly become post-tropical. Gradual weakening is expected through this period, but the global models indicate that Epsilon will continue to produce a very large area of gale-force winds and maximum winds near hurricane strength even after it becomes post-tropical. Epsilon is then expected to merge with another large non-tropical low early next week. The hurricane is accelerating northeastward and should continue to gain forward speed in that general direction for the next day or so. Little change was made to the NHC track forecast, which is based on a blend of TVCA and HCCA. All of the typically reliable track models show the same evolution, so confidence in the track forecast remains high. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 41.3N 56.1W 65 KT 75 MPH 12H 25/1200Z 43.6N 51.4W 60 KT 70 MPH 24H 26/0000Z 47.3N 42.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 26/1200Z 51.6N 30.7W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 27/0000Z 56.5N 23.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 60H 27/1200Z...DISSIPATED $$ Forecaster Zelinsky

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