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Tropical Storm LISA Forecast Discussion Number 11

2016-09-22 10:40:50| National Hurricane Center (Atlantic)

Issued at 500 AM AST THU SEP 22 2016 000 WTNT43 KNHC 220840 TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 500 AM AST THU SEP 22 2016 As anticipated, the southwesterly shear has been gradually increasing, and the center of Lisa is located on the western edge of an area of very deep convection convection. Based on the average of Dvorak estimates, the initial intensity is kept at 40 kt in this advisory. Given that the shear is forecast to increase further, and the fact that Lisa is heading for cooler waters, the NHC forecast calls for weakening. The cyclone is expected to become a remnant low in about 3 days, but this process could even occur much sooner. The intensity forecast is very similar to the previous one. The steering pattern has not changed, and Lisa is moving toward the northwest or 310 degrees around the western side of a weak subtropical ridge. This general track should continue for the next 2 to 3 days until a large mid-latitude trough amplifies and force Lisa or its remnants to recurve. The NHC track forecast is an update of the previous one and follows very closely the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 19.9N 34.0W 40 KT 45 MPH 12H 22/1800Z 20.9N 34.7W 35 KT 40 MPH 24H 23/0600Z 22.3N 36.0W 30 KT 35 MPH 36H 23/1800Z 23.6N 37.3W 30 KT 35 MPH 48H 24/0600Z 25.0N 38.5W 30 KT 35 MPH 72H 25/0600Z 27.5N 41.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/0600Z 31.5N 40.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/0600Z 35.0N 38.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Avila

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Tropical Depression KARL Forecast Discussion Number 31

2016-09-22 04:40:17| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED SEP 21 2016 000 WTNT42 KNHC 220240 TCDAT2 TROPICAL DEPRESSION KARL DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST WED SEP 21 2016 While the convection associated with Karl has become more concentrated to the northwest of the center during the past several hours, dropsonde data from the NOAA G-IV jet indicates that the cyclone's circulation is at least somewhat disorganized. A closed circulation exists from the surface to 700 mb. Above that, there is a poorly defined trough at 500 and 400 mb with southwesterly winds of 10-15 kt above the low level center. Finally, the flow at 300 and 200 mb is from the east and southeast. The maximum surface winds in the dropsonde data were 25 kt, and recent ASCAT data implies maximum winds near 30 kt. Thus, the initial intensity remains 30 kt. The initial motion is 315/13 as Karl continues to move between the southwestern periphery of subtropical ridge and a upper- to mid-level low located north of Puerto Rico. This northwestward track should continue for another 24 hours or so. Beyond that time, Karl should turn northward, move through a break in the ridge, and then accelerate northeastward as it becomes embedded in the westerlies. Since the last advisory, the track guidance has shifted a little to the east during the first 72 hours, and the new forecast track for that period lies between the model consensus and the previous forecast. After recurvature, there remain some differences in the guidance regarding the forward speed of Karl, and the forecast track is in best agreement with a blend of the GFS and HWRF models. While the vertical shear is forecast to gradually decrease over Karl, mid-level moisture values to the southwest of the cyclone remain marginal according to the NOAA jet data. In addition, the disorganized circulation argues against any rapid strengthening. The intensity forecast calls for slow intensification for the next 36 hours, followed by faster strengthening until the 72 hour point when the cyclone is forecast to be a hurricane. Karl should weaken as it begins extratropical transition between 72-96 hours, with the transition to a storm-force extratropical low being complete by 120 hours. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 22.9N 59.6W 30 KT 35 MPH 12H 22/1200Z 24.2N 61.3W 35 KT 40 MPH 24H 23/0000Z 25.9N 63.4W 40 KT 45 MPH 36H 23/1200Z 27.6N 64.3W 45 KT 50 MPH 48H 24/0000Z 29.7N 64.1W 55 KT 65 MPH 72H 25/0000Z 33.5N 58.5W 70 KT 80 MPH 96H 26/0000Z 40.0N 47.0W 70 KT 80 MPH 120H 27/0000Z 47.5N 33.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Tropical Storm LISA Forecast Discussion Number 10

2016-09-22 04:38:20| National Hurricane Center (Atlantic)

Issued at 1100 PM AST WED SEP 21 2016 000 WTNT43 KNHC 220238 TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 1100 PM AST WED SEP 21 2016 Lisa remains a sheared tropical cyclone. Deep convection has expanded in coverage this evening, but recent microwave imagery and ASCAT data indicate that the low-level center is located near the far western edge of the sharp gradient of cold cloud tops. The ASCAT pass did not cover much of the northeastern portion of the circulation, but it did detected a large area of 35 kt winds to the north and north-northeast of the center. Based on these data and satellite estimates of 35 and 45 kt, from SAB and TAFB respectively, the initial intensity remains 40 kt. Lisa is already located within an area of strong upper-level southwesterly winds to the southeast of a large upper-level low. During the next day or two the tropical storm is forecast to approach the cut-off low, which according to the SHIPS model will produce 30-40 kt of shear over Lisa. As a result, the tropical cyclone is expected to weaken and become a remnant low in about 3 days, and it could dissipate before the end of the foreast period. The new NHC intensity forecast essentially an update of the previous forecast and is in best agreement with the SHIPS and LGEM guidance. The microwave and ASCAT fixes suggest that Lisa is moving north-northwestward at about 6 kt, which is a little right of the previous forecasts. The cyclone is expected to move northwestward toward a weakness in the subtropical ridge currently between 30 and 40W. Later in the period, an amplifying mid- to upper-level trough over the western Atlantic should cause Lisa or its remnants to turn northward and recurve into the mid-latitude westerlies by day 5. The track guidance is in fairly good agreement, and only a small eastward adjustment was required during the first 72 hours. The updated track prediction is very close to the latest multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 19.2N 32.8W 40 KT 45 MPH 12H 22/1200Z 20.2N 33.8W 40 KT 45 MPH 24H 23/0000Z 21.6N 35.2W 35 KT 40 MPH 36H 23/1200Z 23.0N 36.5W 30 KT 35 MPH 48H 24/0000Z 24.3N 37.8W 30 KT 35 MPH 72H 25/0000Z 26.7N 40.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/0000Z 31.0N 41.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/0000Z 36.5N 37.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Depression KARL Forecast Discussion Number 30

2016-09-21 22:43:51| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED SEP 21 2016 000 WTNT42 KNHC 212043 TCDAT2 TROPICAL DEPRESSION KARL DISCUSSION NUMBER 30 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 500 PM AST WED SEP 21 2016 The low-level center of Karl appears to have turned toward the northwest with a motion of 305/10 kt based on GOES-East visible imagery, recently tucking underneath the cirrus canopy of developing convection. Though strong at the moment, the deep convection continues to be inconsistent, making the intensity determination a bit muddled. Proximity to NOAA buoy 41044 indicates the circulation appears closed with winds backing from east-northeast to northwest during the past few hours, but there have been no significant pressure falls. ASCAT passes from this morning indicated a broad area of 30-kt winds about 150 n mi to the northeast and east of the center. As such, the initial intensity remains 30 kts at this time. Karl has turned toward northwest as it is being funneled between the southwestern periphery of subtropical ridge and the upper- to mid-level low located north of Puerto Rico and the Virgin Islands. This northwest track should continue through Friday until Karl turns north and rapidly accelerates northeastward, becoming embedded in mid-latitude westerlies. There has been little change in the track guidance, which remains in fairly good agreement through 48 hours. However, differences begin to appear toward the end of the forecast period as the ECMWF continues to be a bit slower. The official forecast remains close to a blend of the GFS and ECMWF but hedges toward the faster GFS solution. This is also in close proximity to the HWRF. Karl's environment continues to gradually improve as the upper low moves westward, reducing vertical wind shear as well supporting a more diffluent upper-level pattern for increased thunderstorm development. However, mid-level moisture values are marginal and may remain as a limiting factor for intensification during the next day or so. Based on the latest intensity guidance, the official forecast now brings Karl back to tropical storm strength over the next day, with intensification continuing through day 4 after the cyclone recurves into the mid-latitude westerlies. Some weakening is possible by the end of the forecast period after Karl's transition to an extratropical cyclone. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 21.9N 58.7W 30 KT 35 MPH 12H 22/0600Z 23.3N 60.7W 35 KT 40 MPH 24H 22/1800Z 24.9N 63.0W 40 KT 45 MPH 36H 23/0600Z 26.5N 64.4W 45 KT 50 MPH 48H 23/1800Z 28.2N 65.0W 50 KT 60 MPH 72H 24/1800Z 31.5N 61.8W 65 KT 75 MPH 96H 25/1800Z 36.6N 51.5W 70 KT 80 MPH 120H 26/1800Z 44.5N 38.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Gallina/Berg

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Tropical Storm LISA Forecast Discussion Number 9

2016-09-21 22:39:17| National Hurricane Center (Atlantic)

Issued at 500 PM AST WED SEP 21 2016 000 WTNT43 KNHC 212039 TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 500 PM AST WED SEP 21 2016 Vertical wind shear of 15-20 kt continues to take a toll on Lisa. The coldest convective tops have moved farther east away from the estimated low-level center position today. Dvorak estimates were T2.5/3.0 from both TAFB and SAB at 18Z, and based on these, the initial intensity has been lowered to 40 kt for this advisory. Given that Lisa has struggled to maintain itself today, and that the SHIPS model shows the shear increasing to 30 kt in the next 18 to 24 hours, there seems to be little opportunity left for the cyclone to strengthen. Given this, the new NHC intensity forecast holds Lisa at 40 kt through 24 hours and then shows gradual weakening to remnant low status in 3 to 4 days as the shear increases to near 40 kt and the mid-level relative humidity drops below 30 percent. This forecast is closest to the SHIPS and LGEM statistical-dynamical models. An AMSR-2 pass from GCOM-W1 from around 1430Z provided some guidance on the center location, but it remains somewhat uncertain given the large spread in the satellite fixes. However, it does appear that the center is located a little to the east of previous estimates, and the initial motion is estimated to be 325/06. The track forecast scenario has not changed, as Lisa is expected to move northwestward into a weakness in the subtropical ridge and then recurve into the mid-latitude flow during the forecast period. Overall, the guidance envelope has shifted eastward this cycle, and given the eastward adjustment in the initial position, the NHC forecast has been shifted eastward by about a degree. The official forecast track is close to a blend of the GFS and ECMWF and lies to the left of multi-model consensus TVCN. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 18.5N 32.5W 40 KT 45 MPH 12H 22/0600Z 19.4N 33.3W 40 KT 45 MPH 24H 22/1800Z 20.8N 34.7W 40 KT 45 MPH 36H 23/0600Z 22.1N 36.0W 35 KT 40 MPH 48H 23/1800Z 23.5N 37.2W 30 KT 35 MPH 72H 24/1800Z 26.0N 40.0W 30 KT 35 MPH 96H 25/1800Z 30.0N 41.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 26/1800Z 36.0N 38.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brennan

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