089 
 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