313 
 WTNT45 KNHC 191434
 TCDAT5
 
 TROPICAL STORM IDA DISCUSSION NUMBER   5
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
 1100 AM AST SAT SEP 19 2015
 
 As was noted yesterday, Ida will have an obstacle course to navigate
 during the next several days, and the storm already appears to have
 encountered its first hurdle.  Westerly shear, on the order of 20 kt
 according to UW-CIMSS analyses, has begun to affect the cyclone, and
 the low-level center is now exposed to the northwest of the deep
 convection.  Dvorak CI numbers remain 2.5, and the initial intensity
 therefore remains 35 kt.  The SHIPS guidance indicates that the
 vertical shear should be steady or even increase slightly during the
 next 24 hours, so only slow strengthening is anticipated during that
 time.  The best window for more significant intensification appears
 to be between 36 and 72 hours when the shear is forecast to
 decrease.  Another round of increased shear on days 4 and 5 should
 limit strengthening or induce weakening.  The intensity models are
 split on Ida's future intensity, with the SHIPS and LGEM models only
 modestly strengthening the cyclone through day 5 while the GFDL and
 HWRF models bring Ida to hurricane strength by day 3.  Due to the
 uncertainty of how Ida will interact with the complex environment
 around it, the NHC intensity forecast is a bit below the intensity
 consensus and is very similar to the previous forecast.
 
 Low- to mid-level ridging to the north and northeast of Ida is
 inducing a slightly faster west-northwestward motion, or 295/10 kt.
 The ridge is expected to weaken within the next 48 hours, leaving
 Ida between two deep-layer lows, one located over the eastern
 Atlantic and the other northeast of the Leeward Islands.  This
 should cause Ida to become nearly stationary or meander by days 3
 through 5. With the exception of the UKMET model, the other track
 models seem to be trending toward a solution in which the eastern
 Atlantic trough has at least some influence on Ida's motion, and the
 updated NHC track forecast now shows a slow eastward drift on days 4
 and 5. Overall though, the NHC track forecast is very similar to the
 previous one and is close to the model consensus aids.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  19/1500Z 14.8N  39.7W   35 KT  40 MPH
  12H  20/0000Z 15.7N  41.4W   40 KT  45 MPH
  24H  20/1200Z 16.9N  43.4W   45 KT  50 MPH
  36H  21/0000Z 18.2N  45.1W   50 KT  60 MPH
  48H  21/1200Z 19.3N  46.5W   55 KT  65 MPH
  72H  22/1200Z 20.5N  47.5W   60 KT  70 MPH
  96H  23/1200Z 20.5N  47.0W   60 KT  70 MPH
 120H  24/1200Z 20.5N  46.5W   55 KT  65 MPH
 
 $$
 Forecaster Berg