366 
 WTNT41 KNHC 102055
 TCDAT1
 
 Hurricane Florence Discussion Number  46
 NWS National Hurricane Center Miami FL       AL062018
 500 PM AST Mon Sep 10 2018
 
 Unfortunately, the models were right. Florence has rapidly
 intensified into an extremely dangerous hurricane, with 30-second
 GOES-16 visible imagery showing well-defined eyewall mesovortices
 rotating inside of the eye. A NOAA Hurricane Hunter aircraft found
 peak SFMR winds of about 120 kt, with flight-level winds and
 dropsonde measurements also supporting that value for the initial
 wind speed estimate. Notably, the aircraft data also show the size
 of the hurricane-force winds has doubled in the past 12 hours.
 
 None of the guidance suggest that Florence has peaked in intensity,
 and this is supported by a continuation of a low-shear environment,
 and even warmer waters over the next 36 hours.  Thus, the intensity
 forecast is raised from the previous one, bringing Florence close
 to category 5 strength tomorrow. Near landfall, the vertical wind
 shear could increase, along with the increasing likelihood of
 eyewall cycles.  While the intensity forecast shows some weakening
 of the maximum winds near landfall, the wind field is expected to
 grow with time, which increases the storm surge and inland wind
 threats.  The bottom line is that there is high confidence that
 Florence will be a large and extremely dangerous hurricane,
 regardless of its exact intensity.
 
 Florence has recently turned west-northwestward, still moving at 11
 kt. The hurricane is expected to accelerate in that direction over
 the next day or two due to building mid-level ridge over the
 northwestern Atlantic Ocean.  By late Wednesday, a turn toward the
 northwest is forecast due to the orientation of the Atlantic ridge,
 along with a decrease in forward speed due to a new ridge building
 over the Great Lakes.  There is a new player in the forecast as
 well, with the disturbance over the northwestern Caribbean adding
 some uncertainty in the ridge strength over the southeastern United
 States.  Perhaps it isn't surprising that the model spread has
 increased on this cycle, with a small eastward shift overall.  The
 official forecast is nudged in the direction of the trend, but is
 west of the model consensus.  It is important not to focus on the
 exact forecast track as average NHC errors at days 4 and 5 are about
 140 and 180 n mi, respectively, and dangerous hazards will extend
 well away from the center.
 
 The NOAA G-IV jet will continue to conduct synoptic surveillance
 missions every 12 h through at least Wednesday. In addition, special
 0600 UTC and 1800 UTC radiosonde launches have been expanded to
 additional upper-air stations across the U.S. are to collect extra
 data for the numerical models.
 
 Key Messages:
 
 1. A life-threatening storm surge is likely along portions of the
 coastlines of South Carolina, North Carolina, and Virginia, and
 a Storm Surge Watch will likely be issued for some of these areas by
 Tuesday morning. All interests from South Carolina into the mid-
 Atlantic region should ensure they have their hurricane plan in
 place and follow any advice given by local officials.
 
 2. Life-threatening freshwater flooding is likely from a prolonged
 and exceptionally heavy rainfall event, which may extend inland over
 the Carolinas and Mid Atlantic for hundreds of miles as Florence is
 expected to slow down as it approaches the coast and moves inland.
 
 3. Damaging hurricane-force winds are likely along portions of the
 coasts of South Carolina and North Carolina, and a Hurricane Watch
 will likely be issued by Tuesday morning. Damaging winds could also
 spread well inland into portions of the Carolinas and Virginia.
 
 4. Large swells affecting Bermuda and portions of the U.S. East
 Coast will continue this week, resulting in life-threatening surf
 and rip currents.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  10/2100Z 25.4N  61.1W  120 KT 140 MPH
  12H  11/0600Z 26.0N  63.2W  130 KT 150 MPH
  24H  11/1800Z 27.0N  66.2W  135 KT 155 MPH
  36H  12/0600Z 28.6N  69.3W  135 KT 155 MPH
  48H  12/1800Z 30.4N  72.2W  130 KT 150 MPH
  72H  13/1800Z 33.7N  77.0W  120 KT 140 MPH
  96H  14/1800Z 35.6N  78.8W   50 KT  60 MPH...INLAND
 120H  15/1800Z 36.5N  79.5W   25 KT  30 MPH...INLAND
 
 $$
 Forecaster Blake