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Tropical Storm KARL Forecast Discussion Number 41

2016-09-24 16:35:39| National Hurricane Center (Atlantic)

Issued at 1100 AM AST SAT SEP 24 2016 000 WTNT42 KNHC 241435 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 41 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 AM AST SAT SEP 24 2016 Data from the last NOAA Hurricane Hunter aircraft mission into Karl earlier this morning found peak flight-level winds of 63 kt at 8,000 ft and a peak SFMR wind of 47 kt. Based on these data, the initial intensity is held at 55 kt for this advisory, but this could be a little generous. The latest minimum central pressure based on a dropsonde from the aircraft is 994 mb. Karl is still expected to strengthen, but it seems likely that this will be at least partly due to baroclinic effects, as the global models shows Karl intensifying while the shear increases to over 50 kt by 24 hours. The new NHC intensity forecast follows this trend, and keeps Karl as a 70-kt cyclone with a very large wind field when it becomes post-tropical in 36 hours. The circulation of Karl should be absorbed by a large extratropical cyclone over the north Atlantic by 48 hours, as shown in the global model solutions. The aircraft last fixed the center on the southeastern side of the deep convection, and the initial motion estimate is now 050/16. Karl should accelerate quickly northeastward ahead of a broad deep-layer trough moving into the Atlantic until it is absorbed, with the forward speed expected to reach 50 kt by 36 hours. The new NHC track forecast is an update of the previous one and remains near the middle of the tightly packed guidance envelope. The track, intensity, and wind radii forecast of Karl's post- tropical phase has been coordinated with the Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 32.8N 62.7W 55 KT 65 MPH 12H 25/0000Z 34.8N 58.8W 60 KT 70 MPH 24H 25/1200Z 38.9N 50.6W 70 KT 80 MPH 36H 26/0000Z 45.0N 39.9W 70 KT 80 MPH...POST-TROPICAL 48H 26/1200Z...ABSORBED $$ Forecaster Brennan

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Tropical Storm KARL Forecast Discussion Number 40

2016-09-24 11:00:07| National Hurricane Center (Atlantic)

Issued at 500 AM AST SAT SEP 24 2016 000 WTNT42 KNHC 240859 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 40 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 AM AST SAT SEP 24 2016 Data from an Air Force Reserve reconnaissance aircraft this morning indicate that Karl has made the much anticipated turn toward the northeast, and that the center has also reached its closest point of approach to Bermuda. The strongest 825-mb flight-level wind measured thus far has been 66 kt and the highest SFMR surface wind measured has been 49 kt. The central pressure of 994 mb is based on a recent dropsonde report. An earlier dropsonde report indicated that the flight-level center was tilted to the northeast of the surface center. Based on these data, the initial intensity is being maintained at 55 kt. The initial motion estimate is 035/15 kt. Karl is now coming under the influence of deep southwesterly steering flow in advance of an approaching strong mid-latitude trough and surface cold front. This flow pattern should keep Karl moving northeastward away from Bermuda and steadily increase its forward speed to 40-45 kt by 36-48 hours. The new forecast track is similar to but slightly to the left of the of the previous advisory track, and lies down the middle of the tightly clustered track guidance. Karl appears to have entrained some dry air in the mid- and low- levels of the atmosphere based on reconnaissance data. However, the cyclone is forecast to remain over SSTs of at least 27 deg C for the next 24 hours or so within an environment of moderate vertical wind shear. This should allow Karl to strengthen to a hurricane in about 24-36 hours. After that, the cyclone is forecast to undergo extratropical transition as it merges with the cold front, and this should be complete by 48 hours, if not sooner. The cyclone is expected to be absorbed by a larger extratropical low between 48-72 hours. The new intensity forecast is similar to the previous advisory and lies close to the consensus model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 31.7N 64.3W 55 KT 65 MPH 12H 24/1800Z 33.5N 61.2W 60 KT 70 MPH 24H 25/0600Z 36.7N 54.9W 65 KT 75 MPH 36H 25/1800Z 41.6N 45.6W 70 KT 80 MPH 48H 26/0600Z 47.6N 36.4W 65 KT 75 MPH...POST-TROP/EXTRATROP 72H 27/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Depression LISA Forecast Discussion Number 19

2016-09-24 10:59:06| National Hurricane Center (Atlantic)

Issued at 500 AM AST SAT SEP 24 2016 000 WTNT43 KNHC 240858 TCDAT3 TROPICAL DEPRESSION LISA DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 500 AM AST SAT SEP 24 2016 A strong burst of convection has recently formed in the northeastern quadrant of Lisa. Overall, however, the system looks less organized than it did yesterday, with the low-level circulation becoming elongated from north to south. The initial wind speed is held at 30 kt in agreement with the TAFB satellite classification. Although there is only limited skill in forecasting deep convection, this burst is expected to be ephemeral due to strong shear and dry air aloft. Thus, Lisa is still forecast to be a remnant low by this evening. The global models show Lisa weakening and opening up into a trough within 2 days, and so will the NHC prediction. The initial motion is a bit faster than earlier, now 315/08. Lisa, or its remnants, are still forecast to move west-northwestward, with a gradual turn toward the north in a day or two while it moves around the periphery of the subtropical high centered near the Azores. The official forecast is close to the previous one and the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 23.8N 37.9W 30 KT 35 MPH 12H 24/1800Z 24.6N 39.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 25/0600Z 26.0N 41.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 25/1800Z 28.0N 42.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 26/0600Z...DISSIPATED $$ Forecaster Blake

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Tropical Storm KARL Forecast Discussion Number 39

2016-09-24 04:52:58| National Hurricane Center (Atlantic)

Issued at 1100 PM AST FRI SEP 23 2016 000 WTNT42 KNHC 240252 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 39 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 1100 PM AST FRI SEP 23 2016 A few hours ago, a NOAA Hurricane Hunter aircraft reported flight-level winds of 71 kt at 7800 ft about 30 n mi to the southwest of the center, along with SFMR surface wind estimates of near 55 kt. The minimum central pressure at the time was near 990 mb. Since then, the cyclone has gotten better organized, with radar data from Bermuda showing a strong convective band west and northwest of the center. One caveat to the increased organization is that the center apparent in both radar and microwave imagery may be a little to the northwest of the surface center. Based on the earlier aircraft data, the initial intensity is set to 55 kt, and this could be a little conservative. Karl is expected to remain over sea surface temperatures of between 29-30C for the next 12-24 hours or so in an environment of moderate vertical wind shear. This should allow the cyclone to strengthen to a hurricane in about 24 hours. After that, the cyclone should undergo extratropical transition as it merges with the cold front, and this should be complete by 48 hours. The cyclone is likely to be absorbed by a larger extratropical low between 48-72 hours. The new intensity forecast is similar to the previous forecast, but it lies a little below the forecasts of the SHIPS and LGEM models. The initial motion is 020/11. Karl is about to enter strong southwesterly flow in advance of a deep-layer trough and associated surface cold front moving eastward from the northeastern United States. This should result in a turn toward the northeast during the next several hours and an increase in forward speed. The new track forecast has changed little from the previous forecast, and calls for Karl to make its closest approach to Bermuda during the next 12 hours and then move rapidly away from the island. Overall, the forecast track is near the center of the tightly clustered guidance. The wind radii have been revised based on a recent scatterometer overpass and input from the Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 30.8N 65.1W 55 KT 65 MPH 12H 24/1200Z 32.5N 63.0W 60 KT 70 MPH 24H 25/0000Z 35.5N 57.8W 70 KT 80 MPH 36H 25/1200Z 39.5N 49.9W 70 KT 80 MPH 48H 26/0000Z 45.0N 40.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 72H 27/0000Z...ABSORBED BY LARGER EXTRATROPICAL LOW $$ Forecaster Beven

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Tropical Depression LISA Forecast Discussion Number 18

2016-09-24 04:49:03| National Hurricane Center (Atlantic)

Issued at 1100 PM AST FRI SEP 23 2016 000 WTNT43 KNHC 240248 TCDAT3 TROPICAL DEPRESSION LISA DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL AL132016 1100 PM AST FRI SEP 23 2016 Lisa continues to suffer from strong vertical wind shear. There has been no deep convection within 120 nm of the center for nearly 12 hours now, though occasional bursts of convection have been noted a little farther than that to the north. A 2324 ASCAT-B pass showed several 35-kt wind vectors between the center and the convection farther to the north. Based on this new information, it is believed that Lisa was still a tropical storm at the time of the previous advisory and at 0000 UTC. Given the lack of deep convection since that time, the initial intensity has been held at 30 kt. Regardless of the maximum winds, the dynamical guidance all suggest that the strong shear and dry mid- and upper-level air will continue to suppress convection near the center, and Lisa is forecast to be declared post-tropical within 12 hours. The remnant circulation should last a day or two after that, before dissipating ahead of a deep-layer trough approaching from the west. The depression may finally be beginning to speed up, and the initial motion estimate is 315/07. The low-level remnants of Lisa are still forecast to move west-northwestward, with a gradual turn toward the north in a day or two while it moves around the periphery of the subtropical high centered near the Azores. The official forecast has again been nudged westward, but lies a little to the right of the model consensus. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 23.2N 37.3W 30 KT 35 MPH 12H 24/1200Z 23.9N 38.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 25/0000Z 25.0N 40.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 25/1200Z 26.4N 42.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 26/0000Z 28.8N 42.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 27/0000Z...DISSIPATED $$ Forecaster Beven/Zelinsky

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