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 154 
 WTNT45 KNHC 220837
 TCDAT5
 
 TROPICAL STORM IDA DISCUSSION NUMBER  16
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
 500 AM AST TUE SEP 22 2015
 
 Shortwave infrared satellite imagery indicates that Ida's low-level
 circulation center is now moving or developing east-southeastward
 closer to the large mass of deep convection that has been persisting
 in the southeastern portion of the larger circulation. The initial
 intensity is being maintained at 40 kt, especially now that the
 low-level center has moved closer to the mid- and upper-level
 circulations as seen in microwave and conventional satellite images.
 This intensity is supported by a Dvorak current intensity estimate
 of T3.0/45 kt from TAFB.
 
 The initial motion estimate is now 105/04 kt. The recent and much
 anticipated turn to the east-southeast appears to have occurred
 either due to actual storm motion or due to redevelopment of the
 low-level center closer to the strong convection. Regardless of the
 cause in the Ida's recent motion change, the global and regional
 models are in very good agreement on a continued general slow motion
 toward the east for the next 48 hours or so as the southern portion
 of a large mid- to upper-level trough moves across and captures the
 cyclone. By 72 hours, the trough lifts out to the northeast and
 releases Ida, allowing the cyclone to move slowly toward the
 northwest by day 4 and toward the north on day 5. As would be
 expected in such a weak flow regime, the model guidance is widely
 divergent after 72 hours with the UKMET, HWRF, and NAVGEM models
 taking Ida more toward the west-northwest, whereas the GFS, ECMWF,
 GFDL, and Canadian models take Ida more toward the northwest and
 north. The one thing that the all of the models do agree on,
 however, is that Ida is not expected move very quickly during the
 next 5 days. The NHC track forecast is similar to but slower than
 the previous advisory track, and lies close to a blend of the
 consensus models TCVA and GFEX.
 
 Given the uncertainty in exactly when and where the low-level center
 of Ida will move underneath the mid/upper-level circulation due to
 fluctuations in the deep-layer vertical shear profiles during the
 next 3 days, the intensity forecast calls for no significant
 changes in the strength of the cyclone during that time. By days 4
 and 5, however, some gradual strengthening is expected as the
 vertical shear abates somewhat while Ida is moving over 29C
 sea-surface temperatures. The official intensity forecast is similar
 to the previous advisory, and closely follows the IVCN intensity
 consensus model.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  22/0900Z 21.3N  48.6W   40 KT  45 MPH
  12H  22/1800Z 21.3N  48.1W   40 KT  45 MPH
  24H  23/0600Z 20.9N  47.3W   40 KT  45 MPH
  36H  23/1800Z 20.6N  46.7W   40 KT  45 MPH
  48H  24/0600Z 20.8N  46.4W   40 KT  45 MPH
  72H  25/0600Z 22.0N  46.7W   40 KT  45 MPH
  96H  26/0600Z 23.0N  48.0W   45 KT  50 MPH
 120H  27/0600Z 25.2N  48.5W   50 KT  60 MPH
 
 $$
 Forecaster Stewart
 
 
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