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Tropical Storm Epsilon Forecast Discussion Number 4

2020-10-20 04:39:45| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Oct 19 2020 000 WTNT42 KNHC 200239 TCDAT2 Tropical Storm Epsilon Discussion Number 4 NWS National Hurricane Center Miami FL AL272020 1100 PM AST Mon Oct 19 2020 Water vapor imagery indicates that Epsilon has been interacting with a shear line/dissipating cold front from the north and with a negatively tilted upper-level trough from the south. Furthermore, a pronounced dry slot has developed in the eastern semicircle, which has severed the convective band that had been wrapping about three-fourths of the way around the circulation. Overall, the cloud pattern more closely resembles that of an occluded extratropical low, with a small inner-core tropical feature. A 20/0025Z ASCAT-A pass indicated a small fetch of mostly straight-flow 40-kt winds located 60-90 nmi northeast of the well-defined surface center. Given the distance from the low-level center and lack of any significant curvature to those winds, undersampling is probably not occurring. Therefore, the initial intensity is being held at 40 kt for this advisory, which is consistent with satellite classifications of T2.5/35 kt from TAFB, SAB, and UW-CIMSS ADT, and a 19/2202Z SATCON estimate of 42 kt. Epsilon is a large cyclone with gale-force or tropical-storm-force winds extending outward more than 250 nmi in the northern semicircle. The initial motion estimate is 360/02 kt. No significant changes were made to the previous track forecast or reasoning. Epsilon is expected to meander within weak steering currents well to the southeast of Bermuda for the next 12 h or so. By late Tuesday, a ridge is forecast to build to the north and east of the cyclone, forcing Epsilon generally toward the northwest through Friday. As an upper-level trough and associated frontal system approach the cyclone, Epsilon is expected to turn sharply northeastward between the trough and the ridge by late Friday, and accelerate northeastward thereafter over over the north Atlantic. The latest NHC model guidance is coming into better agreement, with a tight clustering of he various consensus models lying essentially along the previous advisory track. On the forecast track, Epsilon should make its closest approach to Bermuda on Friday. Epsilon is forecast to remain over sea-surface temperatures (SST) of at least 27C the next 36 h or so and, when coupled with 200-mb temperatures of -55C, sufficient instability will exist to continue to allow for deep convection to be generated both in the inner- and outer-core regions of the cyclone. Thus, gradual strengthening is forecast during that time. However, by 48 h and continuing through 72 h, SSTs cool to near 26.5C and the depth of the relatively warm water becomes quite shallow, as indciated by upper-ocean heat content values dropping to near zero by 72 h. The large and expansive wind field should result in cold upwelling both ahead of and beneath the inner-core wind field, which is likely to temper the intensification process. This may be reflected in the past couple of HRWF runs which no longer make Epsilon a hurricane by the time the cyclone approaches Bermuda on Friday. For now, the intensity forecast has only been lowered slightly since there may be some baroclinic interaction with an approaching upper-level trough that could offset the cooler waters. Epsilon could be undergoing extratropical transition by the 120-h forecast period, but for now the system will be shown as still being tropical since it will be located over marginal SSTs near 26C at that time. Key Message: 1. Epsilon is forecast to be at or near hurricane strength when it approaches Bermuda late this week. While it is too soon to determine the exact details of Epsilon's track and intensity near the island, there is a risk of direct impacts from wind, rainfall, and storm surge on Bermuda, and interests there should closely monitor the progress of Epsilon. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 25.3N 55.3W 40 KT 45 MPH 12H 20/1200Z 26.1N 55.5W 45 KT 50 MPH 24H 21/0000Z 27.5N 56.7W 50 KT 60 MPH 36H 21/1200Z 28.3N 58.5W 55 KT 65 MPH 48H 22/0000Z 29.1N 59.8W 60 KT 70 MPH 60H 22/1200Z 30.4N 60.8W 65 KT 75 MPH 72H 23/0000Z 31.3N 61.5W 70 KT 80 MPH 96H 24/0000Z 32.9N 62.5W 75 KT 85 MPH 120H 25/0000Z 36.4N 60.3W 75 KT 85 MPH $$ Forecaster Stewart

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Tropical Storm Epsilon Forecast Discussion Number 3

2020-10-19 22:51:41| National Hurricane Center (Atlantic)

Issued at 500 PM AST Mon Oct 19 2020 000 WTNT42 KNHC 192051 TCDAT2 Tropical Storm Epsilon Discussion Number 3 NWS National Hurricane Center Miami FL AL272020 500 PM AST Mon Oct 19 2020 Earlier this afternoon, Epsilon had a hybrid-type structure in satellite imagery, with a partially exposed center and a broken convective band that wrapped around the northern and eastern sides of the storm. However, recent satellite imagery shows a small convective burst near the center that gives Epsilon a more tropical appearance. ASCAT-B/C passes from this morning indicate the system has a large and asymmetric wind field, with 34-kt winds extending over 200 nm away from the center in the northern semicircle. This is, in part, attributable to the environmental pressure gradient with a strong high pressure ridge centered east of the Canadian Maritimes. The initial intensity is raised to 40 kt with this advisory, supported by a T2.5 subjective Dvorak classification from TAFB and a 37-kt objective 14Z SATCON estimate. Warm sea-surface temperatures and moderate southwesterly vertical wind shear should allow for gradual strengthening over the next day or so. By 36-48 h, a period of weaker wind shear should allow Epsilon to continue strengthening while becoming better organized and eventually developing a more symmetric wind field. There is still increasing spread in the intensity guidance beyond 48 h, with a split between the stronger statistical-dynamical guidance and the weaker regional hurricane models. Given these mixed signals, little change was made to the intensity forecast with this advisory. The official NHC intensity forecast lies on the higher end of the guidance consensus, but remains lower than SHIPS/LGEM. The official forecast now calls for Epsilon to become a hurricane on Wednesday. Epsilon remains nearly stationary as it meanders over the central Atlantic under weak steering currents. The cyclone should begin moving slowly northward tonight, then turn northwestward with a faster forward speed through midweek as a mid- to upper-level ridge is expected to build to the north and northeast of Epsilon. The current NHC forecast track shows Epsilon making its closest approach to Bermuda on Friday. By this weekend, the cyclone should begin turning northward ahead of an upper-level trough expected to move off the northeastern U.S. coast. Most of the track guidance is tightly clustered for the next several days, except for the latest HWRF. The track guidance has shifted slightly to the right, and so the NHC track forecast has been adjusted similarly to reflect the latest guidance consensus. Key Message: 1. Epsilon is forecast to be at or near hurricane strength when it approaches Bermuda late this week. While it is too soon to determine the exact details of Epsilon's track and intensity near the island, there is a risk of direct impacts from wind, rainfall, and storm surge on Bermuda, and interests there should closely monitor the progress of Epsilon. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 25.5N 55.5W 40 KT 45 MPH 12H 20/0600Z 25.9N 55.5W 45 KT 50 MPH 24H 20/1800Z 27.0N 56.1W 55 KT 65 MPH 36H 21/0600Z 28.1N 57.8W 60 KT 70 MPH 48H 21/1800Z 28.8N 59.4W 65 KT 75 MPH 60H 22/0600Z 29.8N 60.6W 70 KT 80 MPH 72H 22/1800Z 31.1N 61.5W 75 KT 85 MPH 96H 23/1800Z 32.8N 62.8W 80 KT 90 MPH 120H 24/1800Z 35.5N 62.3W 80 KT 90 MPH $$ Forecaster Reinhart/Brown

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Tropical Storm Epsilon Forecast Discussion Number 2

2020-10-19 16:56:34| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Mon Oct 19 2020 000 WTNT42 KNHC 191456 TCDAT2 Tropical Storm Epsilon Discussion Number 2 NWS National Hurricane Center Miami FL AL272020 1100 AM AST Mon Oct 19 2020 Although the center of the system has become exposed over the past few hours, it is very well defined. In addition, the convective banding over the northern and eastern portions of the circulation has continued to improve. Based on a Dvorak classification of T2.5 from TAFB, the system is upgraded to a 35-kt tropical storm. ASCAT-A has missed the circulation, but ASCAT-B caught the far eastern edge of the wind field and indicates winds of 30-35 kt in that area. The tropical storm is located within an environment of moderate southwesterly to westerly vertical wind shear and over warm waters. These conditions should allow for gradual strengthening over the next day or so. By 48 hours, decreasing vertical wind shear could allow for more significant intensification, and there is increasing spread in the intensity guidance by that time. The statistical guidance is at the upper-end of the envelope while the regional hurricane models are lower. The NHC forecast is a bit on the conservative side for now, and lies just above the intensity consensus aids. Given the expected decrease in shear, some upward adjustment in the intensity forecast may be required in subsequent advisories. Epsilon is meandering over the central Atlantic as it is located within an area of weak steering currents near the base of a mid- to upper-level trough that extends southwestward from the northeastern Atlantic. A mid- to upper-level ridge is forecast to build over the western and central Atlantic to the north of the system by midweek, and this ridge should slide eastward later in the week. These changes in the synoptic pattern should cause Epsilon to begin moving west-northwestward to northwestward at a faster rate of speed by midweek. The models are again in fairly good agreement and the NHC track is near the center of the guidance envelope. Key Message: 1. Epsilon is forecast to be at or near hurricane strength when it approaches Bermuda late this week. While it is too soon to determine the exact details of Epsilon's track and intensity near the island, there is a risk of direct impacts from wind, rainfall, and storm surge on Bermuda, and interests there should closely monitor the progress of Epsilon. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 25.6N 55.3W 35 KT 40 MPH 12H 20/0000Z 25.8N 55.1W 40 KT 45 MPH 24H 20/1200Z 26.4N 55.4W 50 KT 60 MPH 36H 21/0000Z 27.6N 56.7W 55 KT 65 MPH 48H 21/1200Z 28.3N 58.5W 60 KT 70 MPH 60H 22/0000Z 29.1N 59.8W 65 KT 75 MPH 72H 22/1200Z 30.2N 60.8W 70 KT 80 MPH 96H 23/1200Z 32.3N 62.7W 75 KT 85 MPH 120H 24/1200Z 34.5N 63.3W 80 KT 90 MPH $$ Forecaster Brown

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Tropical Depression Twenty-Seven Forecast Discussion Number 1

2020-10-19 14:05:33| National Hurricane Center (Atlantic)

Issued at 800 AM AST Mon Oct 19 2020 000 WTNT42 KNHC 191205 TCDAT2 Tropical Depression Twenty-Seven Special Discussion Number 1 NWS National Hurricane Center Miami FL AL272020 800 AM AST Mon Oct 19 2020 Deep convection associated with the area of low pressure over the central Atlantic has become significantly better organized overnight. The low-level center is located near the western edge of the convection, but the system has enough organization to be declared a tropical cyclone. Therefore, advisories are being initiated at this time. The system appears to be near tropical-storm strength, but since earlier classifications were just below that intensity the system is being started as a 30-kt tropical depression. The system appears more tropical than subtropical since it is no longer co-located with an upper-level low and it appears to have a fairly small radius of maximum winds. Therefore, it has been designated a tropical cyclone. Scatterometer data later this morning should provide a better assessment of the system's intensity. The depression is located over SSTs over 27-28 degrees Celsius and within an area of moderate westerly shear. These conditions should allow for gradual strengthening over the next day or so. After that time, the shear is expected to decrease and continued strengthen is anticipated. The NHC intensity forecasts calls for the system to become a hurricane within 72 hours, and is in best agreement with the HCCA and ICON intensity consensus models. The depression is located in an area of weak steering currents near the base of a mid- to upper-level trough that extends southwestward from the northeastern Atlantic. As a result, little net motion is expected through tonight. A mid- to upper-level ridge is forecast to build over the western and central Atlantic to the north of the system by midweek. As the ridge slides eastward later this week, the cyclone should move west-northwestward to northwestward at a faster rate of speed. This motion will bring the system close to Bermuda by late week and the interests on that island should closely monitor the progress of the cyclone. The dynamical models are in relatively good agreement on the overall scenario and the NHC track forecast is near the center of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 19/1200Z 25.8N 55.5W 30 KT 35 MPH 12H 19/1800Z 25.8N 55.4W 35 KT 40 MPH 24H 20/0600Z 26.0N 55.3W 45 KT 50 MPH 36H 20/1800Z 26.9N 55.9W 50 KT 60 MPH 48H 21/0600Z 28.0N 57.8W 55 KT 65 MPH 60H 21/1800Z 28.6N 59.3W 60 KT 70 MPH 72H 22/0600Z 29.5N 60.3W 65 KT 75 MPH 96H 23/0600Z 31.7N 62.3W 70 KT 80 MPH 120H 24/0600Z 33.5N 63.8W 75 KT 85 MPH $$ Forecaster Brown

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Post-Tropical Cyclone Norbert Forecast Discussion Number 26

2020-10-15 10:31:56| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Thu Oct 15 2020 000 WTPZ44 KNHC 150831 TCDEP4 Post-Tropical Cyclone Norbert Discussion Number 26 NWS National Hurricane Center Miami FL EP192020 200 AM PDT Thu Oct 15 2020 Vertical wind shear, cool waters, and a dry and stable atmosphere have taken a toll on Norbert. The system has been devoid of deep convection for more than 12 hours, and therefore it has become a post-tropical cyclone. The initial wind speed is set at 25 kt, which is based on a TAFB Dvorak CI number of T1.5. This could be a little generous as the system has likely continued to spin down since the previous advisory. The remnant low should continue to weaken today, and the global models indicate that the low will open up into a trough of low pressure off the west coast of the Baja California peninsula by tonight. The post-tropical cyclone has slowed down and is now moving north-northwestward at about 6 kt. A slow north-northwestward motion within the weak low-level steering flow is expected until dissipation occurs. This is the last NHC advisory on Norbert. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 26.2N 116.1W 25 KT 30 MPH...POST-TROPICAL 12H 15/1800Z 27.1N 116.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 16/0600Z...DISSIPATED $$ Forecaster Brown

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