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KF5JRV > WX 12.09.18 12:46l 218 Lines 9489 Bytes #999 (0) @ NA
BID : 21136_KF5JRV
Read: GUEST
Subj: NWS NHC Atlantic WX - Sept 12
Path: IW8PGT<CX2SA<HG8LXL<XE1FH<N9PMO<NS2B<KF5JRV
Sent: 180912/1115Z 21136@KF5JRV.#NWAR.AR.USA.NA BPQ6.0.16
564
WTNT41 KNHC 120853
TCDAT1
Hurricane Florence Discussion Number 52
NWS National Hurricane Center Miami FL AL062018
500 AM EDT Wed Sep 12 2018
The eye of Florence remains very distinct in infrared satellite
imagery this morning. There has been little change to the cloud top
temperatures surrounding the eye overnight, however, the overall
cloud shield and central dense overcast has become slightly more
symmetric. An Air Force Reserve Hurricane Hunter aircraft that was
in the hurricane until just after midnight measured a peak 700-mb
flight-level wind of 130 kt, and a SFMR wind of 107 kt in the
northeast eyewall. A blend of these data and recent subjective and
objective satellite intensity estimates supports an initial wind
speed of 115 kt. Florence will be moving over sea surface
temperatures of around 29C and through an area of low vertical wind
shear during the next day or so. These conditions favor some
strengthening, but eyewall replacement cycles could cause some
fluctuations in intensity during that time. After that time, an
increase in southwesterly shear, upwelling, and interaction with
land is likely to lead to some weakening, however, Florence is
expected to remain a dangerous major hurricane as it approaches the
coastline. The new NHC intensity forecast is near the higher
statistical guidance through 48 hours, then follows the trend of
the decay SHIPS model after that time.
Florence is moving west-northwestward or 300 degrees at 15 kt.
There has been no change to the track forecast or reasoning for the
first 36-48 hours, as Florence will continue to be steered
west-northwestward to northwestward around the southwestern portion
of a mid-level ridge centered northeast of Bermuda. By late
Thursday, a mid-level ridge is forecast to begin building over the
east-central United States, which is expected to cause Florence
to slow down significantly by 48 hours. The track guidance is in
good agreement through the first couple of days of the forecast
period, and the NHC track forecast again brings the center of the
hurricane very close to the coasts of North and South Carolina
within 48 hours. Later in the period, the dynamical model spread
increases but most of the guidance has continued its southward
shift, and now take Florence southwestward near the coast of South
Carolina by day 4. The NHC track has been adjusted southward at
days 4 and 5, and is a little north of the consensus out of respect
for continuity, however, the GFS, ECMWF, and the ECMWF ensemble mean
is south of the NHC track forecast, and additional southward
adjustment may be warranted in future advisories.
It is important for users to realize that significant impacts extend
well away from the center of Florence, and serious hazards such as
a dangerous storm surge and flooding rains will cover a large area
regardless of exactly where the center 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 from South Carolina into the mid-Atlantic region 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 and
Mid-Atlantic states from 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 12/0900Z 29.0N 70.1W 115 KT 130 MPH
12H 12/1800Z 30.3N 72.1W 120 KT 140 MPH
24H 13/0600Z 32.0N 74.4W 125 KT 145 MPH
36H 13/1800Z 33.2N 76.1W 120 KT 140 MPH
48H 14/0600Z 33.8N 77.3W 105 KT 120 MPH...NEAR THE COAST
72H 15/0600Z 33.8N 78.2W 85 KT 100 MPH...NEAR THE COAST
96H 16/0600Z 33.6N 79.7W 45 KT 50 MPH...INLAND
120H 17/0600Z 34.2N 82.7W 25 KT 30 MPH...INLAND
$$
Forecaster Brown
ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
Hurricane Helene Discussion Number 20
NWS National Hurricane Center Miami FL AL082018
500 AM AST Wed Sep 12 2018
Earlier this morning, Helene looked quite ragged in IR imagery. The
eye became poorly defined and cloud tops were steadily warming.
However, beginning around 0500 UTC, a new burst of convection began
wrapping around the previously open western portion of Helene's
inner core. Objective and subjective Dvorak current intensity
estimates range from 77 to 91 kt, and the initial intensity is
therefore set at 80 kt as a blend of all of these data.
Despite the fact that Helene appears to be on the upswing at the
moment, the cyclone is still passing over sub-26 deg C waters and
all of the intensity guidance shows weakening for the next 24 h.
Beyond that time, there is still some spread among the intensity
models, though it has decreased since the last advisory. Helene will
begin interacting with a mid-latitude trough over the north-central
Atlantic, which will result in an increase in shear over the
hurricane. However, Helene will also begin to move over warmer
waters and could get some baroclinic support from the upper-level
trough. Overall the intensity guidance is a little lower than
before, and now the NHC intensity forecast is near the middle of the
intensity guidance envelope.
Once again, no meaningful change has been made to the NHC track
forecast which continues to closely follow the HFIP Corrected
Consensus. Helene is moving north-northwestward, and should
gradually turn northward, and eventually northeastward, as the
cyclone is steered between a mid-level ridge to the east and the
aforementioned mid-latitude trough to northwest. The global models
remain in fairly good agreement on the track of Helene, especially
through 72-96 h, when Helene is forecast to pass near the Azores,
and interests in those islands should closely monitor the progress
of Helene over the next several days.
FORECAST POSITIONS AND MAX WINDS
INIT 12/0900Z 19.2N 35.7W 80 KT 90 MPH
12H 12/1800Z 20.7N 36.6W 75 KT 85 MPH
24H 13/0600Z 22.9N 37.2W 65 KT 75 MPH
36H 13/1800Z 25.5N 37.3W 55 KT 65 MPH
48H 14/0600Z 28.9N 36.9W 55 KT 65 MPH
72H 15/0600Z 36.0N 34.3W 50 KT 60 MPH
96H 16/0600Z 41.0N 28.5W 50 KT 60 MPH
120H 17/0600Z 45.5N 19.0W 50 KT 60 MPH
$$
Forecaster Zelinsky
NNNN
274
WTNT44 KNHC 120834
TCDAT4
Tropical Storm Isaac Discussion Number 19
NWS National Hurricane Center Miami FL AL092018
500 AM AST Wed Sep 12 2018
Isaac is a poorly organized tropical storm. Geostationary satellite
and microwave images indicate that the center of the cyclone is
located near the western edge of the main area of deep convection.
This asymmetric cloud pattern is due to about 20 kt of
west-northwesterly shear. The satellite intensity estimates have
been decreasing, and an average of the Dvorak CI-numbers supports
lowering the initial wind speed slightly to 50 kt. The NOAA
Hurricane Hunters are scheduled to investigate Isaac later this
morning, and that data should provide a better assessment of the
storm's intensity and structure.
Isaac continues to move due westward at about 13 kt. The track
forecast reasoning remains unchanged. A fairly strong mid-level
ridge to the north of Isaac should steer the system westward at
about the same forward speed during the next several days. The
models are now in fairly good agreement, and the NHC track forecast
is just a little north of the previous one to come in line with the
latest guidance. Based on this forecast, Isaac is expected to cross
portions of the Leeward and Windward Islands in about 36 hours.
Isaac is feeling the effects of wind shear, and the global models
suggest that the shear will likely remain moderate to strong during
the next couple of days. These hostile winds combined with nearby
dry air will likely cause Isaac to gradually weaken during the next
several days. The intensity models are in fair agreement, and this
forecast is close to the model consensus, except a little lower than
that aid at 96 hours. The latest runs of the GFS and ECMWF models
show Isaac opening up into a trough by day 5, and the NHC forecast
follows those models.
Key Message:
1. Isaac is expected to remain at tropical storm intensity when it
moves across the Lesser Antilles on Thursday, and tropical storm
warnings are in effect for Martinique, Dominica, and Guadeloupe.
Tropical storm watches are in effect for Montserrat, St. Kitts and
Nevis, Antigua, and Saba and St. Eustatius. Interests on those
islands should follow any advice given by their local officials.
FORECAST POSITIONS AND MAX WINDS
INIT 12/0900Z 14.5N 53.5W 50 KT 60 MPH
12H 12/1800Z 14.8N 55.7W 50 KT 60 MPH
24H 13/0600Z 15.0N 58.6W 45 KT 50 MPH
36H 13/1800Z 15.2N 61.5W 45 KT 50 MPH
48H 14/0600Z 15.4N 64.8W 40 KT 45 MPH
72H 15/0600Z 15.3N 70.6W 40 KT 45 MPH
96H 16/0600Z 15.2N 75.0W 35 KT 40 MPH
120H 17/0600Z...DISSIPATED
$$
Forecaster Cangialosi
73 de Scott KF5JRV
Pmail: KF5JRV@KF5JRV.#NWAR.AR.USA.NA
email: KF5JRV@ICLOUD.COM
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