231 
 WTNT41 KNHC 061439
 TCDAT1
 
 Hurricane Florence Discussion Number  29
 NWS National Hurricane Center Miami FL       AL062018
 1100 AM AST Thu Sep 06 2018
 
 Vertical shear has increased since yesterday, which has caused a
 degradation of Florence's structure and a decrease in its maximum
 winds.  The cloud-filled eye has been eroded over the past hour or
 so, and the deep convection is no longer symmetric, with the
 low-level circulation peeking out from under the higher clouds.
 Dvorak CI numbers from TAFB and SAB have fallen to T5.0-5.5 (90-100
 kt), while the objective numbers from UW-CIMSS support 70-90 kt.
 The initial intensity is set at 90 kt, near the middle of this wide
 range of estimates.
 
 The intensity forecast has been somewhat of a self-defeating
 prophecy due to the nuances of the environmental shear.  Even though
 Florence was able to rapidly intensify yesterday in an area just
 south of a zone of strong shear, the hurricane's stronger-than-
 expected intensity caused it to move more poleward, into that
 stronger shear.  Right now, shear analyses range anywhere from
 25-30 kt, and the latest available guidance suggests that this
 level of shear should continue for another 12-24 hours.  As a
 result, continued weakening is forecast over the next day or so.
 After 36 hours, Florence is likely to encounter an upper-level
 environment that is more conducive for reintensification.  The NHC
 forecast is adjusted downward toward the newest consensus aids,
 especially during the first 48 hours, but it still shows Florence
 reaching major hurricane strength again by days 4 and 5.
 
 Florence's forward motion has slowed just a little to 9 kt toward
 the northwest (315 degrees).  A mid-level ridge is building to the
 north, which is likely to cause the hurricane to turn westward by
 36 hours, with that motion continuing through about day 3.  After
 that time, there is still considerable uncertainty in the evolution
 of the steering pattern over the western Atlantic, especially on day
 4.  On one hand, the GFS and HWRF dig a strong shortwave trough over
 Atlantic Canada by Monday, creating a break in the ridge which would
 allow Florence to turn northwestward.  On the other hand, the ECMWF
 and UKMET both have weaker troughs and maintain stronger ridging
 over the northwestern Atlantic, allowing Florence to maintain a
 westward or west-northwestward course.  All the models show a
 mid-level high over the western Atlantic by Tuesday.  Due to typical
 biases among these models in the part of the Atlantic, we prefer to
 be between the GFS and ECMWF solutions at this time, which places
 the official NHC track forecast close to the TVCN multi-model
 consensus and just north of HCCA.
 
 There is still considerable model ensemble spread for Florence's
 track beyond day 5.  Given the large uncertainty at these time
 ranges, it is far too soon to speculate what, if any, impacts
 Florence may have on the U.S. East Coast next week.  Regardless of
 Florence's eventual track, large swells emanating from the hurricane
 will reach Bermuda beginning on Friday and portions of the U.S. East
 Coast this weekend, resulting in life-threatening surf and rip
 currents.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  06/1500Z 24.6N  48.6W   90 KT 105 MPH
  12H  07/0000Z 25.2N  49.8W   80 KT  90 MPH
  24H  07/1200Z 25.6N  51.3W   75 KT  85 MPH
  36H  08/0000Z 25.6N  52.6W   75 KT  85 MPH
  48H  08/1200Z 25.7N  54.0W   80 KT  90 MPH
  72H  09/1200Z 26.3N  56.4W   90 KT 105 MPH
  96H  10/1200Z 28.0N  59.5W  100 KT 115 MPH
 120H  11/1200Z 29.5N  65.0W  105 KT 120 MPH
 
 $$
 Forecaster Berg