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
|