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| #875876 (Received by flhurricane at: 4:57 AM 25.Sep.2016) TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 44 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 500 AM AST SUN SEP 25 2016 Karl continues to produce a large mass of cold-topped convection sheared to the northeast of the low-level center. Some of the cloud tops are as cold as -83 deg C, which is unusual for that far north. Earlier NASA/NOAA Global Hawk aircraft dropsondes measured surface winds as high as 54 kt, and recent satellite intensity estimates from TAFB and UW-CIMSS ADT are 60 kt and 57 kt, respectively. Based on these data, and given that Karl is now moving at a forward speed of at least 40 kt, the initial intensity has been conservatively increased to 60 kt. The initial motion estimate is now 055/40 kt. Karl should continue to move northeastward at 45-50 kt ahead of a broad deep-layer trough until the cyclone is absorbed by a larger extratropical low in about 36 hours. The new official forecast track is just an update of the previous advisory and remains near the middle of the tightly packed guidance envelope, close to the consensus model TVCN and the consensus of the GFS and ECMWF global models. Karl is currently located over a ridge of anomalously warm water with SSTs of 27C to 27.5C, which likely explains the unusually deep and cold-topped convection associated with the cyclone. Karl has about another 6 hours or so over SSTs greater than 26C, which could allow the cyclone to strengthen into a tropical hurricane before it reaches much colder waters. By 12 hours and beyond, Karl will be moving over sea-surface temperatures colder than 20C north of 40N latitude, which will result in the cyclone losing its deep convection and tropical characteristics. However, interaction with the aforementioned deep-layer trough and associated baroclinic energy should help Karl to strengthen into a powerful post-tropical low pressure system possessing hurricane-force winds. By 36 hours, the system should be absorbed into a larger extratropical low to its northwest. The new NHC intensity forecast and wind radii are based on input from the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 37.5N 53.5W 60 KT 70 MPH 12H 25/1800Z 41.3N 46.3W 70 KT 80 MPH...POST-TROPICAL 24H 26/0600Z 48.3N 35.5W 60 KT 70 MPH...POST-TROPICAL 36H 26/1800Z...ABSORBED BY LARGER EXTRATROPICAL LOW $$ Forecaster Stewart |
