Image Department Meteorology
Meteorology_Home Weather_Server News/Seminars
People
Research
Academics Application Contact_Us

Hawaiian_Weather
US_Mainland_Weather
Tropical_Weather
Satellite_Imagery
Radar_Imagery
Marine
Numerical_Models
LAPS
Forecasts
Observations
Archive
Links Disclaimer
Space
SOEST_Home
University_of_Hawaii_Home

 808 
 WTNT41 KNHC 110242
 TCDAT1
 
 Hurricane Florence Discussion Number  47
 NWS National Hurricane Center Miami FL       AL062018
 1100 PM AST Mon Sep 10 2018
 
 The rapid intensification of Florence ended just after the last
 advisory, with the central pressure falling to near 939 mb.  Since
 that time, the eyewall convection has become a bit ragged and the
 latest central pressure from the Air Force Reserve Hurricane Hunter
 aircraft is near 944 mb.  The initial intensity will remain a
 possibly generous 120 kt for this advisory based on the aircraft
 winds.  Microwave imagery suggests that Florence may be starting an
 eyewall replacement cycle.  However, the winds from the Hurricane
 Hunter did not clearly indicate the presence of an outer eyewall.
 
 Florence should remain in a light shear environment and over sea
 surface temperatures near 29C for at least the next 48 h.  Thus,
 there is little other than eyewall replacement cycles to keep the
 hurricane from intensifying further as indicated by all of the
 intensity guidance.  The new intensity forecast calls for continued
 strengthening to near category 5 strength, although at a slower rate
 than what occurred during the last 30 h.  Florence is expected to
 encounter southwesterly shear near the 72 h point, which could
 cause slight weakening before landfall.  However, there remains high
 confidence that Florence will be a large and extremely dangerous
 hurricane, regardless of its exact intensity.
 
 The initial motion is 290/11.  A building mid-level ridge over the
 northwestern Atlantic is expected to steer Florence
 west-northwestward to northwestward with an increase in forward
 speed during the next 48 h.  After that time, a marked decrease in
 forward speed is likely as another ridge builds over the Great
 Lakes to the north of Florence.  The track guidance continues to
 show some spread between the ECMWF on the left side of the envelope
 and the GFS on the right side.  Overall, though, the guidance has
 again shifted a little to the right, and the 72-96 h points are
 nudged just a little to the right from the previous forecast.  It is
 important not to focus on the exact forecast track as average NHC
 errors at days 3, 4, and 5 are about 100, 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. to collect extra data
 for the numerical models.  The next Air Force Reserve Hurricane
 Hunter mission into Florence is scheduled for near 12Z.
 
 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  11/0300Z 25.9N  62.4W  120 KT 140 MPH
  12H  11/1200Z 26.5N  64.5W  125 KT 145 MPH
  24H  12/0000Z 27.9N  67.5W  130 KT 150 MPH
  36H  12/1200Z 29.6N  70.4W  135 KT 155 MPH
  48H  13/0000Z 31.3N  73.2W  130 KT 150 MPH
  72H  14/0000Z 34.0N  76.5W  120 KT 140 MPH
  96H  15/0000Z 35.5N  78.0W   50 KT  60 MPH...INLAND
 120H  16/0000Z 36.5N  79.0W   25 KT  30 MPH...INLAND
 
 $$
 Forecaster Beven
 
 
 
 809 
 WTNT43 KNHC 110242
 TCDAT3
 
 Hurricane Helene Discussion Number  15
 NWS National Hurricane Center Miami FL       AL082018
 1100 PM AST Mon Sep 10 2018
 
 Helene remains a well organized hurricane with a fairly large 25 n
 mi diameter eye and ring of cold cloud tops surrounding that
 feature.  There are a few dry slots beyond the inner core, however,
 which have prevented some of the Dvorak estimates from increasing
 this cycle.  A blend of the latest subjective and objective
 satellite intensity estimates supports raising the initial intensity
 slightly to 95 kt.
 
 The hurricane has a limited amount of time to strengthen as the
 current environment of low wind shear and relatively warm SSTs will
 be changing soon.  Helene is expected to cross the 26 deg C isotherm
 within 24 hours and it will enter an environment of increasing
 south-southwesterly shear just beyond that time period.  These
 conditions should promote a steady weakening trend beginning late
 Tuesday.  By the end of the forecast period, however, SSTs increase
 along the forecast track, and there could be some baroclinic
 enhancements to end the weakening trend and perhaps even cause some
 strengthening.  This scenario is supported by the HWRF/HMON regional
 models and the GFS/ECMWF global models.  The NHC intensity forecast
 is largely an update of the previous one, except it is slightly
 higher at the end of the period.
 
 The hurricane is gradually turning to the right, with the latest
 initial motion estimate being 295/13 kt.  A large mid- to
 upper-level trough over the north Atlantic is expected to dig
 southward causing a significant weakness in the subtropical ridge.
 In response to this change in the steering pattern, Helene is
 forecast to gradually turn northward and then north-northeastward
 during the next several days.  The track models are in fairly good
 agreement, and the NHC track forecast lies near the middle of the
 guidance envelope.  This forecast is only a little to the right of
 the previous track.
 
 FORECAST POSITIONS AND MAX WINDS
 
 INIT  11/0300Z 15.5N  32.4W   95 KT 110 MPH
  12H  11/1200Z 16.2N  34.0W   95 KT 110 MPH
  24H  12/0000Z 17.2N  35.7W   85 KT 100 MPH
  36H  12/1200Z 18.6N  37.2W   75 KT  85 MPH
  48H  13/0000Z 20.1N  38.0W   65 KT  75 MPH
  72H  14/0000Z 24.6N  39.0W   60 KT  70 MPH
  96H  15/0000Z 30.0N  38.0W   50 KT  60 MPH
 120H  16/0000Z 36.2N  34.0W   55 KT  65 MPH
 
 $$
 Forecaster Cangialosi
 
 
Return to the Tropical Systems Page for FLORENCE

Back to main Tropical Weather page




This page is maintained voluntarily by the MKWC and the UHMET faculty, staff, and students.
It was last modified on: Thu, Jul 23 2020 - 2003 UTC
Send comments to: Ryan Lyman