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 284 
 WTPZ44 KNHC 170234
 TCDEP4
 
 TROPICAL STORM OLAF DISCUSSION NUMBER   9
 NWS NATIONAL HURRICANE CENTER MIAMI FL       EP192015
 800 PM PDT FRI OCT 16 2015
 
 The cloud pattern of Tropical Depression Nineteen-E has continued
 to become better organized during the past several hours.  There
 is now a persistent convective area near the center and ragged
 outer bands in the western semicircle.  Satellite intensity
 estimates have increased to 45 kt from SAB and 35 kt from TAFB.  In
 addition, Rapidscat data from the International Space Station showed
 an area of 30-35 kt winds just north of the central convection.
 Based on these data, the depression is upgraded to Tropical Storm
 Olaf with 35 kt winds.
 
 The initial motion estimate is now 270/12.  Olaf is currently being
 steered by a mid-level subtropical ridge.  The dynamical models
 forecast the ridge to persist but weaken during the next 72-96
 hours due to the influence of a strong deep-layer trough forecast
 to develop over the southwestern United States.  This evolution
 should cause Olaf to continue westward with a decrease in forward
 speed during the first 36-48 hours, followed by a west-northwestward
 motion from 48-96 hours. After that time, the ridge is forecast to
 break to the east of the Hawaiian Islands, which should allow the
 storm to turn more northward.  The track guidance is generally in
 good agreement with this scenario, with the ECMWF, GFS, and the
 various consensus models rather tightly clustered.  The new
 forecast track is similar to the previous track through 72 hours,
 then is nudged slightly westward thereafter.  The new track is
 close to the model consensus.
 
 Olaf is expected to remain in an environment of good moisture,
 light shear, and warm sea surface temperatures for at least the
 next three days, so there is no obvious reason it should not
 strengthen.  On one side of the guidance, the LGEM forecasts Olaf
 to become a major hurricane in 72 hours, and the Rapid
 Intensification Index of the SHIPS model shows a 30-35 percent
 chance of 30 kt of strengthening during the next 24 hours.  On the
 other side, the GFDL and HWRF forecast a much slower rate of
 intensification. The new intensity forecast is nudged upward from
 the previous forecast based on current trends and is a compromise
 between the SHIPS model and the Florida State Superensemble.  As
 stated in the previous advisory, given the very conducive
 large-scale environment, it would not be surprising to see more
 strengthening than is currently forecast.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  17/0300Z  9.7N 127.6W   35 KT  40 MPH
  12H  17/1200Z  9.7N 129.1W   45 KT  50 MPH
  24H  18/0000Z  9.7N 130.8W   55 KT  65 MPH
  36H  18/1200Z 10.0N 132.4W   65 KT  75 MPH
  48H  19/0000Z 10.5N 133.9W   75 KT  85 MPH
  72H  20/0000Z 12.0N 137.0W   95 KT 110 MPH
  96H  21/0000Z 14.0N 140.0W   95 KT 110 MPH
 120H  22/0000Z 16.5N 141.5W   90 KT 105 MPH
 
 $$
 Forecaster Beven
 
 
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