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Tropical Storm KARL Forecast Discussion Number 25
2016-09-20 16:36:14| National Hurricane Center (Atlantic)
Issued at 1100 AM AST TUE SEP 20 2016 000 WTNT42 KNHC 201436 TCDAT2 TROPICAL STORM KARL DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122016 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM AST TUE SEP 20 2016 Karl's center remains exposed to the southwest of the deep convection, as it appears that the cyclone has been unable to escape the influence of a mid-/upper-level low to its west. Dvorak Current Intensity estimates remain 3.0 from TAFB and 2.5 from SAB, and the latest UW-CIMSS ADT estimate is T2.5. The initial intensity is therefore held at 35 kt. SHIPS and UW-CIMSS shear analyses indicate that the vertical shear that has been affecting Karl has not yet decreased, but it is now southerly at around 15 kt. The global models continue to indicate that the shear should decrease during the next few days, but this probably won't happen until Karl becomes more separated from the upper-level low. The thermodynamic environment has improved slightly since yesterday, as the cyclone appears to be associated with a large moisture envelope with mid-level relative humidities increasing into the 50 percent range. Little change in strength is likely during the next 24 hours, but after that time intensification is expected due to warm SSTs, more moisture, and lower shear. The official intensity forecast continues to show Karl as a hurricane in the 3-5 day range, but the updated forecast has been nudged downward slightly based on the latest guidance. The new forecast is very close to SHIPS guidance and is near the upper end of the guidance envelope. Karl's center has been straddling the 20th parallel, but the 12-hour motion estimate is 275/15 kt. Karl should be reaching the western extent of the subtropical high during the next 48 hours, and its motion should therefore turn northwestward by day 2 and then northward by day 4. After that time, the cyclone is expected to accelerate toward the northeast when it gets picked up by the mid-latitude westerlies ahead of a trough. The cross-track spread in the guidance has decreased since yesterday for the time period when Karl recurves, although there are significant speed differences after recurvature. Most notably, the ECMWF is significantly slower than the other models and doesn't show Karl being picked up as quickly by the mid-latitude trough. To split the difference, the updated track forecast is very similar to the previous one and is close to a consensus of the GFS and ECMWF. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 20.0N 54.3W 35 KT 40 MPH 12H 21/0000Z 20.7N 56.0W 35 KT 40 MPH 24H 21/1200Z 21.9N 58.3W 35 KT 40 MPH 36H 22/0000Z 23.5N 60.5W 45 KT 50 MPH 48H 22/1200Z 25.1N 62.7W 55 KT 65 MPH 72H 23/1200Z 27.6N 65.2W 70 KT 80 MPH 96H 24/1200Z 31.0N 63.5W 85 KT 100 MPH 120H 25/1200Z 36.5N 54.5W 90 KT 105 MPH $$ Forecaster Berg/Krekeler
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