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Hurricane Oscar Forecast Discussion Number 14

2018-10-30 09:34:52| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Oct 30 2018 000 WTNT41 KNHC 300834 TCDAT1 Hurricane Oscar Discussion Number 14 NWS National Hurricane Center Miami FL AL162018 500 AM AST Tue Oct 30 2018 Oscar's eye is less distinct on infrared satellite imagery than it was several hours ago. Conventional and microwave imagery suggest that the center is tilted a bit to the northeast with height, and there continues to be some erosion of convection over the southwestern quadrant of the hurricane. This is indicative of some southwesterly shear over the system, and Oscar does not appear likely to strengthen further. The current intensity is held at 90 kt based on a blend of Dvorak Current Intensity numbers from TAFB and SAB. Model guidance indicates that the shear will not increase further until tonight, so the intensity is held steady for the next 12 hours. After that time, south-southwesterly shear if forecast to increase and become quite high in 36-48 hours. Around that time, global models show Oscar interacting with a frontal zone, and causing significant warm and cold air advection around the center, indicating the transition to a vigorous extratropical cyclone. Not surprisingly, the global guidance also shows a substantial increase in the size of the system during and after the extratropical transformation, and this is reflected in the NHC wind radii forecasts. Oscar is beginning to move faster, just to the east of due north, or around 010/11 kt. There is little change to the track forecast reasoning from the previous advisory. Over the next couple of days, Oscar should continue to accelerate, toward the north-northeast, in the flow on the southeast side of a mid-latitude trough that has just moved off the United States east coast. Later in the period, post-tropical Oscar should become more embedded within the trough and in the mid-latitude westerlies, and move northeastward over the northeastern Atlantic. The official track forecast is similar to the previous one and is a blend of the simple and corrected dynamical model consensus predictions. Large swells from Oscar will affect Bermuda through Wednesday. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 28.6N 58.2W 90 KT 105 MPH 12H 30/1800Z 30.6N 57.1W 90 KT 105 MPH 24H 31/0600Z 34.0N 54.3W 85 KT 100 MPH 36H 31/1800Z 38.5N 50.5W 80 KT 90 MPH 48H 01/0600Z 43.5N 46.7W 65 KT 75 MPH...POST-TROP/EXTRATROP 72H 02/0600Z 50.5N 35.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 03/0600Z 57.5N 21.5W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 04/0600Z 63.0N 9.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Hurricane Oscar Forecast Discussion Number 13

2018-10-30 03:42:21| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Oct 29 2018 000 WTNT41 KNHC 300242 TCDAT1 Hurricane Oscar Discussion Number 13 NWS National Hurricane Center Miami FL AL162018 1100 PM AST Mon Oct 29 2018 The satellite presentation of Oscar continued to improved after the release of the previous advisory, with the small eye becoming a little more distinct around 0000 UTC, but it has again become cloud filled within the past hour or so. Recent microwave imagery continues to depict a tiny eye with a solid ring of deep convection surrounding it, but there is little outer banding over the southwestern portion of the circulation likely due to shear and dry air. Objective satellite intensity estimates which may be having trouble discerning the small eye are around 80 kt, while subjective T-numbers range from T5.0 from SAB to T5.5 from TAFB. As a result, the initial intensity has been increased to 90 kt for this advisory. Although the NHC intensity forecast does not explicitly show additional strengthening, Oscar has another 12 hours or so over SSTs of 26-26.5 deg C in which some slight intensification could occur. After that time, increasing southwesterly shear and cooler waters along the forecast track should cause the hurricane to weaken gradually as extratropical transition begins. Oscar is forecast to complete extratropical transition in about 48 hours, and remain a powerful post-tropical cyclone over the north Atlantic for much of the forecast period. The global models indicate that Oscar's wind field will quickly expand during its transition to a post-tropical cyclone, and this is reflected in the NHC wind radii forecast. The hurricane has been moving slightly east of due north or 010/8 kt. Oscar is forecast to begin to accelerate north-northeastward or northeastward ahead of a deep-layer trough that will be moving over the western Atlantic on Tuesday. The hurricane should be well embedded within the deep-layer southwesterly flow ahead of the trough by Tuesday night or Wednesday, and the cyclone is expected to move rapidly northeastward across the north-central and northeastern Atlantic later this week. There has been little change to the guidance envelope, and the new NHC track forecast is essentially an update of the previous advisory. The official forecast again lies near the various consensus aids and is near the middle of the tightly clustered model guidance. Although Oscar is not expected to directly affect any land areas, large swells from Oscar will affect Bermuda through Wednesday. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 27.4N 58.3W 90 KT 105 MPH 12H 30/1200Z 28.8N 57.7W 90 KT 105 MPH 24H 31/0000Z 31.5N 55.6W 85 KT 100 MPH 36H 31/1200Z 35.3N 52.1W 80 KT 90 MPH 48H 01/0000Z 40.1N 47.8W 70 KT 80 MPH...POST-TROP/EXTRATROP 72H 02/0000Z 49.1N 36.4W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 03/0000Z 56.2N 22.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 04/0000Z 62.5N 9.5W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Hurricane Oscar Forecast Discussion Number 12

2018-10-29 21:32:50| National Hurricane Center (Atlantic)

Issued at 500 PM AST Mon Oct 29 2018 000 WTNT41 KNHC 292032 TCDAT1 Hurricane Oscar Discussion Number 12 NWS National Hurricane Center Miami FL AL162018 500 PM AST Mon Oct 29 2018 The overall cloud pattern of Oscar is somewhat asymmetrical, and convective banding is limited to the eastern semicircle of the cyclone. However, recent visible and microwave imagery indicate that tight eyewall of the hurricane is still very well defined, despite the 20 kt or more of westerly shear analyzed in SHIPS and UW-CIMSS diagnostics. It appears that the shear is not having much of an affect on Oscar's inner-core, and in fact the small eye of the hurricane has become better defined over the past 6 hours. Recent objective and subjective intensity estimates support an intensity of 75-80 kt, and given the small radius of maximum winds (RMW) of Oscar, it seems more appropriate to round up, yielding an estimated intensity of 80 kt. All of the dynamical intensity guidance calls for additional intensification in the short term. Persistent lightning inside the hurricane's RMW during the past several hours also supports the notion of additional strengthening, as this signal has been associated with intensifying hurricanes in the past. By 24 h and beyond, Oscar will likely level off in intensity and then begin to weaken while it moves over much cooler SSTs and begins extratropical transition. Although this process will likely result in a rapid expansion of Oscar's tropical-storm-force wind field, it should also cause the maximum winds associated with the cyclone to steadily decrease through the end of the week. The NHC intensity forecast is similar to the previous advisory, and generally follows IVCN through the forecast period. Oscar's eye has wobbled during the past several hours, but the hurricane appears to have already begun its expected turn toward the north. The hurricane is essentially on-track, and no major changes were required to the NHC track forecast. A large mid-latitude trough to the west will likely cause Oscar to accelerate north-northeastward or northeastward beginning by late Tuesday, and then rapidly move across the northern central Atlantic in that direction. The global models are in reasonably good agreement on the speed and heading of Oscar through day 5, which is somewhat unusual for a recurving cyclone. The new official track forecast is based on a blend of the simple and corrected multi-model consensus aids, and confidence in the track forecast is fairly high. Although Oscar is not expected to directly affect any land areas, large swells from Oscar will affect Bermuda through Wednesday. Please consult products from your local weather office as these conditions could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 26.5N 58.5W 80 KT 90 MPH 12H 30/0600Z 27.8N 58.4W 90 KT 105 MPH 24H 30/1800Z 29.9N 57.2W 90 KT 105 MPH 36H 31/0600Z 33.0N 54.3W 85 KT 100 MPH 48H 31/1800Z 37.3N 50.3W 80 KT 90 MPH 72H 01/1800Z 46.7N 40.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 02/1800Z 54.0N 25.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 03/1800Z 60.0N 12.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Zelinsky

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Hurricane Oscar Forecast Discussion Number 11

2018-10-29 15:34:47| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Mon Oct 29 2018 000 WTNT41 KNHC 291434 TCDAT1 Hurricane Oscar Discussion Number 11 NWS National Hurricane Center Miami FL AL162018 1100 AM AST Mon Oct 29 2018 Oscar's convective cloud pattern has continued to improve since the previous advisory, with a small, cloud-filled eye now apparent in visible satellite imagery and also in a recent SSMI/S microwave pass. In addition, cirrus outflow has been expanding in all quadrants, especially in the eastern semicircle. The initial intensity of 75 kt is based on a Dvorak satellite intensity estimate of T4.5/77 kt from TAFB, a Data-T-number of T4.5/77 kt from SAB, and an NHC objective intensity estimate of T4.4/75 kt. It is also worth noting that bursts of lightning activity in the eastern eyewall have been occurring since around 1100 UTC. The initial motion estimate is now 285/06 kt. Oscar has slowed its forward motion significantly and has made the advertised turn toward the west-northwest. A motion toward the northwest is expected by late afternoon today as the hurricane rounds the southwestern periphery of a deep-layer ridge. A turns toward the north and then toward the north-northeast are forecast on Tuesday as Oscar moves north of the ridge axis ahead of an eastward-moving deep-layer trough currently approaching Bermuda. The trough is expected to continue advancing eastward over the next couple of days, accelerating Oscar toward the northeast at forward speeds near 25 kt on Wednesday through Friday. Although a strong shortwave trough is still forecast to dig southward to the west of Oscar on Wednesday, none of the model guidance shows the hurricane being captured any longer, and instead keep the cyclone as a separate entity that accelerates northeastward into the mid-latitude westerlies as a strong extratropical cyclone. The official track forecast is similar to the previous advisory, and lies close to an average of the corrected-consensus models HCCA and FSSE and the simple consensus models TVCA and TVCX. Deep-layer (850-200 mb) shear calculations by the SHIPS model and UW-CIMSS are at least 25 kt from the northwest, which clearly is not negatively affecting the improving cirrus outflow. This is likely due to the large 1000-km domain that the SHIPS model uses to compute vertical wind shear. Furthermore, most of the cloud top temperatures within the outflow layer appear to be mostly below the 200-mb level, and closer to the 250-mb level. The large shear values are resulting in much less intensification forecast by the SHIPS and LGEM statistical-dynamical intensity models. As a result, the official intensity forecast leans more toward the HCCA and FSSE models, which are weighing more heavily the stronger intensity forecasts provided by the HWRF, HMON, and Navy COAMPS-TC models, which have Oscar strengthening to just below major hurricane status in 24-36 hours. By 48 hours and beyond, sharply decreasing SSTs along with increasing southwesterly shear ahead of a deep-layer trough are expected to cause Oscar to gradually weaken and transition to a strong extratropical low in 60-72 hours. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 25.8N 58.4W 75 KT 85 MPH 12H 30/0000Z 26.8N 58.7W 85 KT 100 MPH 24H 30/1200Z 28.7N 58.0W 90 KT 105 MPH 36H 31/0000Z 31.4N 56.1W 90 KT 105 MPH 48H 31/1200Z 35.0N 52.6W 80 KT 90 MPH 72H 01/1200Z 43.0N 43.7W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 02/1200Z 50.0N 30.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 03/1200Z 55.0N 15.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Hurricane Oscar Forecast Discussion Number 10

2018-10-29 09:35:47| National Hurricane Center (Atlantic)

Issued at 500 AM AST Mon Oct 29 2018 000 WTNT41 KNHC 290835 TCDAT1 Hurricane Oscar Discussion Number 10 NWS National Hurricane Center Miami FL AL162018 500 AM AST Mon Oct 29 2018 The cloud pattern of Oscar has continued to become better organized, with a growing CDO and convective banding features are better defined, especially over the southern semicircle of the hurricane. Upper-level outflow is gradually becoming better established to the south. Although the most recent Dvorak Current Intensity estimates from TAFB and SAB are at 65 kt, given that the eye is becoming better defined, the advisory intensity is set at 70 kt. Oscar is currently under some northerly to north-northwesterly shear, but the shear is expected to diminish somewhat later today. Also, the tropical cyclone is expected to move through a modestly moist air mass for the next day or two. Therefore, additional strengthening is forecast through 36 hours in agreement with the latest intensity model consensus. Around 48 hours into the forecast period, the shear begins to increase significantly, with notably cooler SSTs. This should lead to the onset of a steady weakening trend. By about 72 hours, the global models indicate that Oscar will become embedded in a frontal zone, so the official forecast shows the system becoming an extratropical cyclone at that time. Oscar has slowed its forward motion and is now moving at about 270/11 kt. A mid-level high to the north of the cyclone is expected to quickly shift eastward, while a mid-latitude trough approaches Oscar from the west in a day or so. This evolution of the steering flow should cause Oscar to turn northward to north-northeastward in 24-48 hours. Later in the forecast period, Oscar is likely to move quickly northeastward on the eastern side of the trough. There has been some inconsistencies in the track model guidance around 5 days over the last few forecast cycles, with the model consensus, TVCN, shifting significantly southward and then northward. The official forecast track is somewhat to the left of the previous one near the end of the period, to reflect the latest consensus prediction. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 25.7N 57.8W 70 KT 80 MPH 12H 29/1800Z 26.1N 58.7W 75 KT 85 MPH 24H 30/0600Z 27.7N 58.7W 80 KT 90 MPH 36H 30/1800Z 30.0N 57.5W 85 KT 100 MPH 48H 31/0600Z 33.0N 54.7W 85 KT 100 MPH 72H 01/0600Z 41.5N 46.5W 70 KT 80 MPH...POST-TROP/EXTRATROP 96H 02/0600Z 46.0N 35.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 03/0600Z 48.0N 26.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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