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 641 
 WTNT41 KNHC 282045
 TCDAT1
 
 TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER   4
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL112015
 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
 500 PM EDT MON SEP 28 2015
 
 The low-level center has become well exposed due to continued
 northwesterly shear of 20 kt or more, with the mid-level
 center displaced well to the southeast of the low-level center.
 Flight-level and SFMR-observed wind data from an Air Force
 reconnaissance aircraft showed that the maximum winds remain near
 30 kt.  This is also consistent with the latest Dvorak estimates
 from SAB and TAFB.
 
 The center of the depression has been moving well to the left of
 the previous track, with the initial motion estimated to be 270/05
 kt.  In addition to the more westward initial motion, there have
 been significant changes in the model guidance, with the latest
 ECMWF forecast taking the cyclone much farther south and west than
 the GFS in 3-5 days.  This appears to be the result of enhanced
 mid-level ridging to the north of the cyclone in the ECMWF at that
 time frame.  This has necessitated a significant southwestward
 shift of the official forecast, although for continuity the new NHC
 track does not take the cyclone as far to the southwest as the
 ECMWF.  Given the large spread now seen in the dynamical track
 guidance, confidence in the track forecast is rather low.
 
 The strong shear over the system is likely to continue for at least
 the next 12-24 hours and given the large displacement between the
 low- and mid-level centers, no intensification is anticipated in
 the short term.  The dynamical guidance indicates some relaxation
 of the shear in a day or two, so the official forecast shows the
 cyclone strengthening into a tropical storm later on Tuesday.  This
 is close to the intensity model consensus through 48 hours, and a
 little below it thereafter.  Given the large uncertainty in the
 track forecast, there is also uncertainty as to what kind of
 environment the cyclone will encounter during the forecast period,
 which also leads to low confidence in the official intensity
 forecast.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  28/2100Z 27.5N  70.2W   30 KT  35 MPH
  12H  29/0600Z 27.7N  71.0W   30 KT  35 MPH
  24H  29/1800Z 27.9N  72.0W   35 KT  40 MPH
  36H  30/0600Z 28.3N  72.8W   40 KT  45 MPH
  48H  30/1800Z 28.6N  73.4W   45 KT  50 MPH
  72H  01/1800Z 30.0N  74.0W   45 KT  50 MPH
  96H  02/1800Z 33.0N  74.0W   45 KT  50 MPH
 120H  03/1800Z 38.5N  73.5W   45 KT  50 MPH
 
 $$
 Forecaster Pasch/Hayes
 
 
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