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Tropical Storm Karen Forecast Discussion Number 21

2019-09-27 10:50:51| National Hurricane Center (Atlantic)

Issued at 500 AM AST Fri Sep 27 2019 981 WTNT42 KNHC 270850 TCDAT2 Tropical Storm Karen Discussion Number 21 NWS National Hurricane Center Miami FL AL122019 500 AM AST Fri Sep 27 2019 Karen's status as a tropical cyclone is becoming increasingly dubious. In a trio of ASCAT passes that arrived yesterday evening, the circulation of the cyclone was indistinguishable from a surface boundary that extends south from the remnants of post-tropical cyclone Jerry. This suggests that Karen's circulation may no longer be well-defined. Furthermore, deep convection near the center of Karen has generally decreased and become less organized since last night. Satellite-based intensity estimates support maintaining the intensity of Karen at 35 kt, but this could be generous given that the max winds observed in the earlier ASCAT data were lower. Regardless of the exact starting intensity of the cyclone, gradual weakening is expected for the next few days. There is unanimous agreement among the dynamical models on this scenario. Simulated satellite imagery from the GFS and ECMWF models show the cyclone devoid of deep convection within 36 hours, if not sooner. Increasingly hostile upper-level winds should then prevent the cyclone from reorganizing and it is forecast to dissipate in about four days. It has been difficult to locate the center of Karen overnight and the initial motion estimate is uncertain but also unchanged (055/7 kt). The global models are forecasting that Karen will continue to move on this general heading through this morning before it stalls tonight. A building ridge to the north should cause Karen or its remnants to start moving westward over the weekend. FORECAST POSITIONS AND MAX WINDS INIT 27/0900Z 28.3N 61.2W 35 KT 40 MPH 12H 27/1800Z 28.8N 60.1W 35 KT 40 MPH 24H 28/0600Z 29.1N 59.6W 30 KT 35 MPH 36H 28/1800Z 29.3N 60.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 29/0600Z 29.3N 61.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 30/0600Z 29.0N 64.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0600Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Karen Forecast Discussion Number 20

2019-09-27 04:33:50| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Sep 26 2019 000 WTNT42 KNHC 270233 TCDAT2 Tropical Storm Karen Discussion Number 20 NWS National Hurricane Center Miami FL AL122019 1100 PM AST Thu Sep 26 2019 The center of the circulation of Karen moved near or over the NOAA buoy 41049 where a wind shift and a very modest drop in pressure occurred. Currently, the winds are decreasing and pressures are rising at the buoy. The data from the buoy and recent satellite imagery continue to indicate that the circulation remains elongated with the low-level center located on the eastern edge of a convective mass. However, some curved rainbands are developing on the eastern portion of the circulation as we speak. T-numbers from SAB and TAFB are 2.5 on the Dvorak scale and support a generous initial intensity of 35 kt. A very recent partial ASCAT pass measured winds of only 30 kt, but the swath did not cover the area where the plane measured stronger winds earlier today. In about a day, the upper-level environment will become increasingly hostile with the development of northwesterly shear, and thereafter, the shear will become even stronger from the southwest. With this anticipated upper-level wind pattern, Karen should weaken and become devoid of deep convection in 36 hours or so and degenerate into a remnant low. Karen has slowed down and is now moving toward the northeast or 055 degrees at 7 kt. The steering flow is forecast to change in 24 hours as a ridge builds to the north of Karen, and the cyclone, or most likely its remnants, should begin to move slowly westward. The system is anticipated to degenerate into a westward moving trough in 3 days or so as forecast by global models. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 27.8N 62.1W 35 KT 40 MPH 12H 27/1200Z 28.3N 61.0W 35 KT 40 MPH 24H 28/0000Z 28.5N 60.0W 30 KT 35 MPH 36H 28/1200Z 28.5N 60.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 29/0000Z 28.3N 61.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 30/0000Z 28.0N 64.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0000Z...DISSIPATED $$ Forecaster Avila

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Hurricane Lorenzo Forecast Discussion Number 18

2019-09-27 04:33:18| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Sep 26 2019 243 WTNT43 KNHC 270233 TCDAT3 Hurricane Lorenzo Discussion Number 18 NWS National Hurricane Center Miami FL AL132019 1100 PM AST Thu Sep 26 2019 Lorenzo has intensified even more this evening, with a clear eye characterized by warm temperatures of up to 17 degrees Celsius. The eye is now completely surrounded by a ring of convection with cold cloud tops less than minus 70 degrees Celsius. The subjective Dvorak intensity estimates from both TAFB and SAB, as well as the objective intensity estimate from UW-CIMSS ADT unanimously support increasing the initial intensity to 125 kt. Lorenzo is a very large hurricane, with tropical storm force winds extending over 200 n mi from the center in the northern semicircle, and a cirrus cloud canopy that spans greater than a 10 degree latitude by 10 degree longitude area. The initial motion is now north-northwest, or 330/12 kt. Model guidance is in very good agreement throughout the 5 day period on the future track of Lorenzo. The hurricane will move through a break in the subtropical ridge currently to its northwest over the next couple of days, gradually turning to the north then northeast as it rounds the periphery of a ridge to its east. Late in the forecast period, Lorenzo will begin to accelerate as it gets caught in southwesterly flow ahead of an approaching mid-latitude trough. The model guidance made a slight shift to the left since the previous advisory, but since the same guidance shifted right earlier today, I did not want to make much of a change to the track. The official forecast track is very near the previous one, and is now on the right side of the consensus guidance. The environment around Lorenzo is expected to change little over the next day or so. Both dynamical and statistical guidance are suggesting that the hurricane is nearing peak intensity. Therefore only fluctuations in strength due to eyewall replacement cycles are expected through about Friday night. Over the weekend, some moderate westerly shear ahead of the approaching mid-latitude trough could begin to slowly weaken the cyclone. Late in the forecast period, the combination of strong upper level southwesterly winds and cooler sea surface temperatures should cause a faster weakening trend. The official forecast is essentially an update of the previous one, and a little higher than most of the guidance through the first 48 hours. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 17.6N 41.5W 125 KT 145 MPH 12H 27/1200Z 19.1N 42.3W 125 KT 145 MPH 24H 28/0000Z 21.0N 43.3W 120 KT 140 MPH 36H 28/1200Z 22.7N 43.8W 115 KT 130 MPH 48H 29/0000Z 24.4N 43.6W 110 KT 125 MPH 72H 30/0000Z 27.8N 41.8W 100 KT 115 MPH 96H 01/0000Z 31.8N 39.0W 95 KT 110 MPH 120H 02/0000Z 37.5N 33.2W 85 KT 100 MPH $$ Forecaster Latto

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Hurricane Lorenzo Forecast Discussion Number 17

2019-09-26 22:48:14| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Sep 26 2019 000 WTNT43 KNHC 262048 TCDAT3 Hurricane Lorenzo Discussion Number 17 NWS National Hurricane Center Miami FL AL132019 500 PM AST Thu Sep 26 2019 Lorenzo has continued to intensify this afternoon, as the 20 n mi wide eye has become better defined and the cloud tops in the eyewall have gotten colder. Various subjective and objective satellite intensity estimates are now in the 115-125 kt range, so the initial intensity is increased to a possibly conservative 120 kt. The hurricane has excellent outflow in all directions except to the west, where it is starting to interact with an upper-level trough. The hurricane has turned toward the northwest since the last advisory, with the 12-h average motion now 310/10 kt and the shorter term motion is even more toward the north. Lorenzo is approaching a break in the subtropical ridge caused by a series of mid-latitude troughs to the northwest of the hurricane, and the track guidance models remain in excellent agreement that Lorenzo should recurve through the break during the forecast period. After 24-36 h, the guidance has shifted a little more to the right, and this part of the new track forecast has been nudged a little to the right. Data from the SHIPS model suggest that Lorenzo will be in an area of maximum potential intensities of 125-135 kt for the next 3-4 days. This suggests that the current intensification should end soon as the actual intensity approaches or reaches those speeds. Fluctuations in strength due to eyewall replacement cycles are expected during the 12-24 h period. The global models suggest that Lorenzo's interaction with the aforementioned upper-level trough should increase during recurvature, which should cause increased shear and a gradual weakening of the cyclone. As Lorenzo subsequently moves northeastward in the mid-latitude westerlies, increased shear and cooler sea surface temperatures should lead to at least a continued slow weakening. The new intensity forecast has only minor changes from the previous forecast. While its exact ranking will be determined later, Lorenzo is one of the largest and most powerful hurricanes of record for the central tropical Atlantic, with the only comparable hurricane in recent times near there being Gabrielle of 1989. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 16.5N 40.8W 120 KT 140 MPH 12H 27/0600Z 17.6N 41.9W 125 KT 145 MPH 24H 27/1800Z 19.6N 43.0W 120 KT 140 MPH 36H 28/0600Z 21.3N 43.6W 115 KT 130 MPH 48H 28/1800Z 22.9N 43.8W 110 KT 125 MPH 72H 29/1800Z 26.5N 42.3W 100 KT 115 MPH 96H 30/1800Z 30.5N 39.5W 95 KT 110 MPH 120H 01/1800Z 35.5N 35.0W 90 KT 105 MPH $$ Forecaster Beven

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Tropical Storm Karen Forecast Discussion Number 19

2019-09-26 22:35:19| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Sep 26 2019 000 WTNT42 KNHC 262035 TCDAT2 Tropical Storm Karen Discussion Number 19 NWS National Hurricane Center Miami FL AL122019 500 PM AST Thu Sep 26 2019 Data from aircraft reconnaissance, ASCAT, and NOAA buoy 41049 indicate that Karen's circulation is becoming increasingly elongated. A combination of data from these platforms also supports maintaining an initial intensity of 40 kt for now. The deterioration of Karen's structure suggests that weakening is imminent, especially with an expected increase in northerly shear during the next day or so. The GFS and ECMWF models--via their simulated infrared satellite fields--are unanimous in showing Karen losing its organized deep convection in about 36 hours. Based on that, the new NHC forecast depicts Karen as becoming a remnant low in 48 hours. Due to a significant increase in southwesterly shear by day 4, the system is expected to open up into a surface trough by day 5. Fixes suggest that Karen is slowing down a bit and turning to the right, with an initial motion of 025/10 kt. The steering flow will be evolving over the next couple of days with high pressure building to the north of Karen over the western Atlantic. This will cause the cyclone to almost come to a stop in about 36 hours, and then turn to the west by 48 hours until dissipation on day 5. This is the same forecast reasoning as before, and the new NHC forecast is just an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 27.2N 62.9W 40 KT 45 MPH 12H 27/0600Z 27.9N 61.8W 35 KT 40 MPH 24H 27/1800Z 28.2N 60.6W 35 KT 40 MPH 36H 28/0600Z 28.1N 60.3W 30 KT 35 MPH 48H 28/1800Z 28.0N 61.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 29/1800Z 27.9N 63.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 30/1800Z 27.9N 66.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 01/1800Z...DISSIPATED $$ Forecaster Berg

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