038 
 WTNT45 KNHC 240843
 TCDAT5
 
 TROPICAL STORM IDA DISCUSSION NUMBER  24
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
 500 AM AST THU SEP 24 2015
 
 Ida's low-level center is exposed to the west of a relatively small
 cluster of deep convection due to 25 kt of west-northwesterly shear.
 By themselves, satellite intensity estimates would no longer
 support Ida's status as a tropical storm, but the partial ASCAT
 passes from last evening had just enough wind that I'm hesitant to
 downgrade the system to a tropical depression just yet.  Vertical
 shear is expected to decrease only slightly during the next couple
 of days, and along with abundant mid-level dry air, the environment
 will not be particularly favorable for strengthening.  The GFDL,
 which brings Ida to hurricane strength in 4 days, remains an outlier
 and is discounted as a reasonable solution.  Conversely, the ECMWF
 and GFS global models show Ida weakening as a result of the
 unfavorable environment, with the GFS even showing the cyclone
 degenerating to a trough by day 4 or 5.  Because of these more
 believable scenarios, the NHC intensity forecast is a little lower
 than the previous one at the end of the forecast period, and
 overall is very close to the Florida State Superensemble.
 
 Ida had been moving east-southeastward during the past 12 hours,
 but the current motion estimate is 090/5 kt.  Ida remains located
 within the base of a mid-tropospheric trough, but it should become
 detached from the trough during the next 24 hours and turn
 northward as low- to mid-level ridging develops over the eastern
 Atlantic.  Now that the global models have been trending toward a
 weaker system by days 3 through 5, they show Ida becoming blocked
 by a surface high over the north Atlantic and moving westward at a
 faster forward speed by the end of the forecast period.  The
 updated NHC track forecast is a little faster than and southwest of
 the previous forecast at days 4 and 5 to account for the model
 trends, but it is otherwise very similar before those times.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  24/0900Z 19.6N  45.5W   35 KT  40 MPH
  12H  24/1800Z 20.2N  45.4W   35 KT  40 MPH
  24H  25/0600Z 20.8N  45.4W   35 KT  40 MPH
  36H  25/1800Z 21.6N  45.8W   35 KT  40 MPH
  48H  26/0600Z 22.5N  46.5W   35 KT  40 MPH
  72H  27/0600Z 23.8N  48.2W   40 KT  45 MPH
  96H  28/0600Z 23.5N  50.0W   40 KT  45 MPH
 120H  29/0600Z 23.0N  52.5W   40 KT  45 MPH
 
 $$
 Forecaster Berg