480 
 WTNT45 KNHC 202045
 TCDAT5
 
 TROPICAL STORM IDA DISCUSSION NUMBER  10
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
 500 PM AST SUN SEP 20 2015
 
 Deep convection associated with Ida has decreased in coverage and
 become somewhat less organized today.  The tropical cyclone remains
 sheared with a small band of convection located well east of the
 exposed center.  Although Dvorak satellite T-numbers have decreased
 this afternoon, the initial intensity remains 40 kt, which is based
 on the earlier ASCAT data.
 
 Ida is moving northwestward or 305 degrees at 15 kt, a little faster
 than this morning.  Despite the recent increase in forward speed,
 Ida is expected to slow down during the next 24 hours, and become
 nearly stationary by Tuesday when a mid-level ridge builds to the
 north of the system.  Ida is then forecast to meander for a couple
 of days, before the ridge slides eastward and allows the tropical
 cyclone to resume a northwestward motion.  The track guidance is in
 good agreement during the first few days of the forecast, but again
 becomes quite divergent by the end of the forecast period.  The
 ECMWF, which moves Ida more eastward during the next few days, is
 along the eastern edge of the guidance envelope.  Meanwhile the
 UKMET and GFS show less of an eastern motion while the steering
 currents are weak, and take Ida more westward by day 5.  The updated
 NHC track is between these scenarios and remains close to the
 multi-model consensus at 96 and 120 h.
 
 The westerly shear is still expected to decrease during the next
 day or so, but given the current organization of the system, Ida
 may not be able to take full advantage of the potentially more
 favorable upper-air pattern.  Therefore, only a slight increase in
 intensity is predicted.  After 48 hours, upper-level westerly winds
 associated with a trough are forecast to cause an increase in shear
 over the cyclone, which would likely cause weakening.  The global
 models, however, generally deepen the cyclone between 72 and 120 h
 when Ida interacts with an upper-level trough.  The official
 forecast shows little change in strength late in the period and
 lies between these differing possibilities.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  20/2100Z 18.4N  46.3W   40 KT  45 MPH
  12H  21/0600Z 19.6N  47.5W   40 KT  45 MPH
  24H  21/1800Z 20.9N  48.5W   45 KT  50 MPH
  36H  22/0600Z 21.5N  48.7W   45 KT  50 MPH
  48H  22/1800Z 21.5N  48.5W   45 KT  50 MPH
  72H  23/1800Z 21.0N  48.2W   45 KT  50 MPH
  96H  24/1800Z 20.9N  48.5W   45 KT  50 MPH
 120H  25/1800Z 22.5N  49.5W   45 KT  50 MPH
 
 $$
 Forecaster Brown