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Wednesday, September 12, 2018

Florence Once a Category 4 Hurricane Drops to Category 3 Questionably (Might Even Be Category 2)

942 
WTNT31 KNHC 121841 CCA
TCPAT1

BULLETIN
Hurricane Florence Intermediate Advisory Number 53A...Corrected
NWS National Hurricane Center Miami FL       AL062018
200 PM EDT Wed Sep 12 2018

Corrected formatting of pressure in summary section

...FLORENCE'S PEAK WINDS HAVE DECREASED SLIGHTLY BUT THE SIZE OF THE
WIND FIELD HAS INCREASED...
...LIFE-THREATENING STORM SURGE AND RAINFALL EXPECTED ACROSS
PORTIONS OF THE CAROLINAS...

Hurricane Hunter Data from Dropsondes (Image From TropicalTidbits.com)


SUMMARY OF 200 PM EDT...1800 UTC...INFORMATION
----------------------------------------------
LOCATION...30.4N 71.8W
ABOUT 435 MI...700 KM SE OF WILMINGTON NORTH CAROLINA
ABOUT 470 MI...755 KM ESE OF MYRTLE BEACH SOUTH CAROLINA
MAXIMUM SUSTAINED WINDS...125 MPH...205 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...948 MB...27.99 INCHES

















WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY:

None.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Storm Surge Warning is in effect for...
* South Santee River South Carolina to Duck North Carolina
* Albemarle and Pamlico Sounds, including the Neuse and Pamlico
Rivers

A Storm Surge Watch is in effect for...
* Edisto Beach South Carolina to South Santee River South Carolina
* North of Duck North Carolina to the North Carolina/Virginia border

A Hurricane Warning is in effect for...
* South Santee River South Carolina to Duck North Carolina
* Albemarle and Pamlico Sounds

A Hurricane Watch is in effect for...
* Edisto Beach South Carolina to South Santee River South Carolina

A Tropical Storm Warning is in effect for...
* North of Duck North Carolina to the North Carolina/Virginia border

A Tropical Storm Watch is in effect for...
* North of the North Carolina/Virginia border to Cape Charles Light
Virginia
* Chesapeake Bay south of New Point Comfort

Interests elsewhere in the southeastern and mid-Atlantic states
should monitor the progress of Florence.

A Storm Surge Warning means there is a danger of life-threatening
inundation, from rising water moving inland from the coastline,
during the next 36 hours in the indicated locations. For a
depiction of areas at risk, please see the National Weather
Service Storm Surge Watch/Warning Graphic, available at
hurricanes.gov.  This is a life-threatening situation.  Persons
located within these areas should take all necessary actions to
protect life and property from rising water and the potential for
other dangerous conditions.  Promptly follow evacuation and other
instructions from local officials.

A Storm Surge Watch means there is a possibility of life-
threatening inundation, from rising water moving inland from the
coastline, in the indicated locations during the next 48 hours.

A Hurricane Warning means that hurricane conditions are expected
somewhere within the warning area.  A warning is typically issued
36 hours before the anticipated first occurrence of tropical-storm-
force winds, conditions that make outside preparations difficult or
dangerous.  Preparations to protect life and property should be
rushed to completion.

A Hurricane Watch means that hurricane conditions are possible
within the watch area.  A watch is typically issued 48 hours
before the anticipated first occurrence of tropical-storm-force
winds, conditions that make outside preparations difficult or
dangerous.

A Tropical Storm Warning means that tropical storm conditions are
expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.

For storm information specific to your area, including possible
inland watches and warnings, please monitor products issued by your
local National Weather Service forecast office.


DISCUSSION AND OUTLOOK
----------------------
At 200 PM EDT (1800 UTC), reports from An Air Force Reserve
reconnaissance aircraft indicate that the center of the eye of
Hurricane Florence was located near latitude 30.4 North, longitude
71.8 West. Florence is moving toward the northwest near 16 mph (26
km/h) and this general motion, accompanied by a gradual decrease in
forward speed, is expected to through Saturday. On the forecast
track, the center of Florence will move over the southwestern
Atlantic Ocean between Bermuda and the Bahamas today, and approach
the coast of North Carolina or South Carolina in the hurricane
warning area on Thursday and Friday and move slowly near the
coastline through Saturday.

The reconnaissance aircraft found that maximum sustained winds have
decreased to near 125 mph (205 km/h) with higher gusts. Florence is
now a category 3 hurricane on the Saffir-Simpson Hurricane Wind
Scale.  Some fluctuations in strength will be possible through
Thursday morning.  Although slow weakening is expected to begin by
late Thursday, Florence is still forecast to be an extremely
dangerous major hurricane when it nears the U.S. coast late Thursday
and Friday.

Hurricane-force winds extend outward up to 70 miles (110 km) from
the center and tropical-storm-force winds extend outward up to 175
miles (280 km).  A NOAA buoy located about 100 miles northeast of
Florence's eye recently reported a sustained wind of 53 mph (85
km/h) and a gust to 74 mph (119 km/h).

The minimum central pressure based on reports from the
reconnaissance aircraft is estimated to be 948 mb (27.99 inches).


HAZARDS AFFECTING LAND
----------------------
STORM SURGE:  The combination of a dangerous storm surge and the
tide will cause normally dry areas near the coast to be flooded by
rising waters moving inland from the shoreline.  The water has the
potential to reach the following heights above ground if peak surge
occurs at the time of high tide...

Cape Fear NC to Cape Lookout NC, including the Neuse, Pamlico,
Pungo, and Bay Rivers...9-13 ft
North Myrtle Beach SC to Cape Fear NC...6-9 ft
Cape Lookout NC to Ocracoke Inlet NC...6-9 ft
South Santee River SC to North Myrtle Beach SC...4-6 ft
Ocracoke Inlet NC to Salvo NC...4-6 ft
Salvo NC to North Carolina/Virginia Border...2-4 ft
Edisto Beach SC to South Santee River SC...2-4 ft

The deepest water will occur along the immediate coast in areas of
onshore winds, where the surge will be accompanied by large and
destructive waves.  Surge-related flooding depends on the relative
timing of the surge and the tidal cycle, and can vary greatly over
short distances.  For information specific to your area, please see
products issued by your local National Weather Service forecast
office.

RAINFALL:  Florence is expected to produce heavy and excessive
rainfall in the following areas...

Coastal North Carolina...20 to 30 inches, isolated 40 inches. This
rainfall would produce catastrophic flash flooding and significant
river flooding.

South Carolina, western and northern North Carolina...5 to 10
inches, isolated 20 inches.
Elsewhere in the Appalachians and Mid-Atlantic states...3 to 6
inches, isolated 12 inches.

WIND:  Hurricane conditions are expected to reach the coast within
the hurricane warning area late Thursday or Friday.  Winds are
expected to first reach tropical storm strength on Thursday, making
outside preparations difficult or dangerous.  Preparations to
protect life and property should be rushed to completion.

TORNADOES:  A few tornadoes are possible in eastern North Carolina
beginning late Thursday morning.

SURF:  Swells generated by Florence are affecting Bermuda, portions
of the U.S. East Coast, and the northwestern and central Bahamas.
These swells are likely to cause life-threatening surf and rip
current conditions. Please consult products from your local weather
office.

An Air Force Reserve hurricane hunter aircraft investigating
Florence this morning has found no change in the hurricane's peak
intensity of 115 kt, even though the central pressure had decreased
a few millibars down to 943 mb. However, the aircraft data do
indicate that Florence's inner-core wind field has expanded, with
the 50-kt wind radii now extending outward up to 100 n mi to the
northeast. Florence still has a very distinct eye in satellite
imagery, but cloud top temperatures have been waxing and waning in
the eyewall region, with slight downward trend noted in the past
hour or so. In contrast, the upper-level outflow remains impressive
and continues to expand everywhere except to the south.

Florence is now moving toward the northwest or 305/13 kt. There has
been no significant change to the NHC model guidance, including the
corrected-consensus models HCCA and FSSE, which are now virtually
on top of each other and the simple consensus model TVCA. As a
result, no changes were required to the previous NHC track. The
shortwave trough over the southern Plains seen in water vapor
imagery could end up being a significant factor as it rounds the
narrow ridge over the Tennessee Valley and is expected to erode the
ridge along the U.S. mid-Atlantic coast on days 3-5. At this time,
little change has been made to the NHC track forecast, which remains
very close to the aforementioned consensus aids through 72 hours. On
the current forecast track, the center of Florence is expected to be
near the coasts of southern North Carolina and northern South
Carolina in 48 to 72 hours and then drift westward to west-
southwestward in weak steering flow.

There is still a narrow window of opportunity for Florence to
strengthen a little when the cyclone moves over the warmest SSTs and
highest upper-ocean heat content while the shear will be the lowest
between 0600-1200 UTC tomorrow morning. After that, decreasing ocean
heat content along with the slowing forward speed of Florence should
cause at least some cold upwelling beneath the hurricane, which
should induce a gradual weakening trend. Once Florence reaches the
shallow coastal shelf waters in 72 h, land interaction and more
significant upwelling are expected, further enhancing the weakening
process. The NHC intensity forecast remains near the higher
statistical guidance through 48 hours, then follows the trend of the
decay SHIPS model after that time.

While Florence's maximum winds are expected to weaken a little, it
is still expected to remain a dangerous major hurricane as it
approaches the coast. The threat to life from storm surge and
rainfall will not diminish, and these impacts will cover a large
area regardless of exactly where the center of Florence moves.

Key Messages:

1. A life-threatening storm surge is now highly likely along
portions of the coastlines of South Carolina and North Carolina, and
a Storm Surge Warning is in effect for a portion of this area.  All
interests in these areas should complete preparations and follow any
advice given by local officials.

2. Life-threatening, catastrophic flash flooding and significant
river flooding is likely over portions of the Carolinas late this
week into early next week, 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 Warning
is in effect. Strong winds could also spread inland into portions
of the Carolinas.

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  12/1500Z 29.8N  71.3W  115 KT 130 MPH
 12H  13/0000Z 31.1N  73.1W  120 KT 140 MPH
 24H  13/1200Z 32.6N  75.1W  125 KT 145 MPH
 36H  14/0000Z 33.5N  76.5W  120 KT 140 MPH
 48H  14/1200Z 33.8N  77.4W  105 KT 120 MPH...NEAR THE COAST
 72H  15/1200Z 33.6N  78.4W   85 KT 100 MPH...NEAR THE COAST
 96H  16/1200Z 33.6N  80.4W   45 KT  50 MPH...INLAND
120H  17/1200Z 34.7N  82.8W   25 KT  30 MPH...INLAND
NEXT ADVISORY ------------- Next complete advisory at 500 PM EDT. $$ Forecaster Stewart