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 663 
 WTNT41 KNHC 100248
 TCDAT1
 
 Hurricane Florence Discussion Number  43
 NWS National Hurricane Center Miami FL       AL062018
 1100 PM AST Sun Sep 09 2018
 
 Florence's satellite appearance has continued to improve quite
 markedly since the previous advisory. An eye was evident in GOES-16
 high-resolution infrared imagery and other channels between
 2300-0000 UTC, but it became cloud covered immediately thereafter
 due to a strong burst of deep convection in the southern and eastern
 eyewall where cloud tops colder than -80C and an abundance of
 lightning activity was observed. Since that time, the CDO has
 expanded and become more circular, outflow has increased and become
 more symmetrical, and an eye has begun to re-appear. The initial
 intensity has been increased to 80 kt for this advisory based on a
 subjective Dvorak intensity estimate of T4.5/77 kt from SAB and NHC
 objective intensity estimates ranging from 77 kt to 87 kt.
 
 The initial motion estimate is 280/06 kt. Once again, there is no
 significant change to the previous forecast track or synoptic
 reasoning. The models appear to be getting better dialed in on both
 the location and strength of the developing blocking ridge in the
 vicinity of Bermuda during the next 4 days as the mid-latitude flow
 amplifies across the CONUS and the northwestern Atlantic. In fact,
 the global models are now in very good agreement on forecasting
 Florence's upper-level mass outflow being deposited to the north and
 east of the hurricane, which will act to further strengthen the
 blocking ridge and help to drive the hurricane northwestward toward
 the southeastern U.S. coastal region. The new NHC model guidance is
 even more tightly packed about the previous forecast track, with
 less than a 90 n mi cross-track spread at 72 h and less than 120 n
 mi spread at 96 h, just prior to expected landfall. Therefore, the
 new official advisory track is essentially just an update and
 extension of the previous forecast, and lies between the nearly
 juxtaposed HCCA and FSSE corrected consensus track models.
 
 Now that Florence has developed an inner-core ring of deep
 convection, which has insulated the eye from intrusions of dry air,
 rapid intensification appears likely to begin soon and continue for
 the next 36 hours or so due to the expected very low vertical wind
 shear conditions, dual outflow jet pattern that will be developing,
 and very warm SSTs of 29-29.5 deg C beneath the hurricane. The most
 favorable combination of the aforementioned factors will occur in
 about 48 h, and that's when Florence is likely to achieve its
 maximum intensity.  After 72 hours, the wind shear is expected to
 increase to around 10-15 kt from the south or southwest, and the
 dual outflow pattern is forecast to change to only a single poleward
 outflow pattern. This slight degradation in the upper-level
 environment, along with slightly cooler SSTs, is expected to result
 in a gradual weakening of the powerful cyclone. However, Florence is
 still forecast to be near category-4 strength when the dangerous
 hurricane makes landfall. The official intensity forecast is an
 average of the intensity forecast from the corrected consensus
 models HCCA and FSSE, with the latter explicitly forecasting a peak
 intensity of 134 kt in 72 hours. It is also worth noting that the
 model guidance is also significantly increasing the size of
 Florence's wind field over the next few days, and the official
 forecast reflects this trend.
 
 The NOAA G-IV jet will conduct another synoptic surveillance
 mission early Monday morning in support of the 1200 UTC model
 cycle, and these flights will continue through Tuesday. In addition,
 upper-air stations across portions of the central and eastern U.S.
 are conducting special 0600 UTC and 1800 UTC radiosonde launches to
 collect extra data for the numerical models. Hopefully these data
 will help improve the track and intensity forecasts.
 
 Key Messages:
 
 1. There is an increasing risk of two life-threatening impacts from
 Florence: storm surge at the coast and freshwater flooding from a
 prolonged heavy rainfall event inland. While it is too soon to
 determine the exact timing, location, and magnitude of these
 impacts, interests at the coast and inland from South Carolina into
 the mid-Atlantic region should closely monitor the progress of
 Florence, ensure they have their hurricane plan in place, and follow
 any advice given by local officials.
 
 2. Large swells affecting Bermuda and portions of the U.S. East
 Coast will continue this week.  These swells will result in
 life-threatening surf and rip currents.
 
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  10/0300Z 24.6N  57.7W   80 KT  90 MPH
  12H  10/1200Z 24.9N  59.1W   90 KT 105 MPH
  24H  11/0000Z 25.6N  61.5W  105 KT 120 MPH
  36H  11/1200Z 26.5N  64.4W  120 KT 140 MPH
  48H  12/0000Z 27.8N  67.6W  130 KT 150 MPH
  72H  13/0000Z 31.2N  73.6W  130 KT 150 MPH
  96H  14/0000Z 34.0N  77.5W  120 KT 140 MPH
 120H  15/0000Z 35.2N  79.0W   55 KT  65 MPH...INLAND
 
 $$
 Forecaster Stewart
 
 
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