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KF5JRV > WX 10.09.18 12:45l 221 Lines 9543 Bytes #999 (0) @ NA
BID : 21020_KF5JRV
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Subj: NWS NHC Atlantic WX - Sept 10
Path: IW8PGT<CX2SA<HP2BWJ<LU4ECL<XE1FH<W9ABA<N9LYA<KF5JRV
Sent: 180910/1115Z 21020@KF5JRV.#NWAR.AR.USA.NA BPQ6.0.16
672
WTNT41 KNHC 100906 CCA
TCDAT1
Hurricane Florence Discussion Number 44...CORRECTED
NWS National Hurricane Center Miami FL AL062018
500 AM AST Mon Sep 10 2018
Corrected to reflect that the 96 hour forecast point is inland.
Florence is rapidly strengthening this morning. The satellite
presentation has improved markedly overnight with a small 10-n-mi
wide-eye becoming apparent in infrared satellite pictures. The
upper-level outflow continues to expand over the northern and
northwestern portions of the storm, but is somewhat restricted over
the southeastern quadrant. Dvorak satellite classifications from
TAFB and SAB supported an intensity of around 80 kt at 0600 UTC, but
with the cooling of the cloud tops around the eye since that time,
the initial intensity has been increased to 90 kt for this advisory.
Satellite fixes indicate that Florence has turned west-northwestward
(285 degrees), and is moving at a slightly faster forward speed of
8 kt. A high pressure ridge building to the north and northwest of
Florence is expected to steer the hurricane west-northwestward to
northwestward at a much faster forward speed over the southwest
Atlantic during the next few days. After that time, a building
ridge over the Ohio Valley is expected to cause a gradual reduction
in the forward speed of the cyclone as it approaches the
southeastern United States coastline. The latest run of the ECMWF
has shifted southwestward, along with its ensemble suite, while
there was little overall change in the GFS and its ensemble. On
the other hand, the UKMET shifted northeastward and is now along
the right side of the guidance envelope. With these changes to the
guidance, the overall spread has increased this cycle, however, the
corrected consensus aids (FSSE and HCCA) are not much different
than before, and the NHC track again follows these models very
closely. Users are cautioned to not focus on the exact forecast
track as the average NHC errors at days 4 and 5 are about 140
and 180 n mi, respectively.
Florence will be traversing very warm SSTs of around 29C and
remain within a very favorable upper-level environment during the
next couple of days. These conditions are expected to lead to
significant strengthening during the next 12 to 24 hours, and
Florence is forecast to be a very powerful major hurricane on
its approach to the southeastern United States. The NHC intensity
forecast is slightly above all of the intensity guidance during the
first 24 hours, and is then a blend of the FSSE and HCCA models.
The global model guidance also increases the size of Florence's wind
field during the next few days, and this has been reflected in
the NHC wind radii forecast.
The NOAA G-IV jet is conducting another synoptic surveillance
mission this morning in support of the 1200 UTC model cycle, and
these flights will continue through Tuesday. A NOAA P-3 Hurricane
Hunter aircraft is also scheduled to conduct a research mission
into Florence this morning, with Air Force C-130 fix missions
beginning late this afternoon. Additional upper-air data are
being collected across portions of the central and eastern U.S.
via special 0600 UTC and 1800 UTC radiosonde launches. Hopefully
these data will help improve the track and intensity forecasts.
Key Messages:
1. There is an increasing risk of life-threatening impacts from
Florence: storm surge at the coast, freshwater flooding from a
prolonged and exceptionally heavy rainfall event inland, and
damaging hurricane-force winds. 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 10/0900Z 24.9N 58.9W 90 KT 105 MPH
12H 10/1800Z 25.4N 60.5W 110 KT 125 MPH
24H 11/0600Z 26.1N 63.1W 120 KT 140 MPH
36H 11/1800Z 27.3N 66.2W 125 KT 145 MPH
48H 12/0600Z 28.8N 69.3W 130 KT 150 MPH
72H 13/0600Z 32.2N 74.8W 125 KT 145 MPH
96H 14/0600Z 34.5N 78.1W 100 KT 115 MPH...INLAND
120H 15/0600Z 35.8N 79.6W 40 KT 45 MPH...INLAND
$$
Forecaster Brown
739
WTNT43 KNHC 100852
TCDAT3
Hurricane Helene Discussion Number 12
NWS National Hurricane Center Miami FL AL082018
500 AM AST Mon Sep 10 2018
Little change in the Helene's cloud pattern has been observed
during the past 6 hours. The earlier mentioned ragged banding-type
eye feature is still apparent in the enhanced infrared BD-curve
imagery and a recent SSMI/S microwave overpass. The initial
intensity is held at 75 kt, and is based on the subjective Dvorak
intensity estimates.
Helene is moving within a fairly ripe environment and over warm
oceanic sea surface temperatures. These conducive conditions
should promote additional strengthening over the next 36 hours.
Afterward, increasing south-southwesterly shear, lower
mid-tropospheric moisture, and cooler water are expected to induce
weakening, however gradually, through day 5. The official forecast
follows suit and is similar to the better performing IVCN intensity
consensus model.
Helene's initial motion is estimated to be west-northwestward, or
285/15 kt, and this general motion is forecast during the next 48
hours. Beyond that period, a break in the subtropical ridge to the
northwest of Paul, created by a mid- to upper-level cut-off low
digging southward, should induce a northward turn with a gradual
increase in forward motion. The large-scale models all indicate
this change in the synoptic steering pattern, although there is some
disparity on how soon Helene will turn toward the north. The NHC
track is quite close to the previous forecast and lies between the
consensus guidance.
FORECAST POSITIONS AND MAX WINDS
INIT 10/0900Z 14.3N 28.9W 75 KT 85 MPH
12H 10/1800Z 14.8N 30.9W 80 KT 90 MPH
24H 11/0600Z 15.5N 33.4W 85 KT 100 MPH
36H 11/1800Z 16.3N 35.6W 85 KT 100 MPH
48H 12/0600Z 17.2N 37.2W 80 KT 90 MPH
72H 13/0600Z 20.3N 39.4W 65 KT 75 MPH
96H 14/0600Z 25.3N 40.8W 55 KT 65 MPH
120H 15/0600Z 31.2N 41.1W 50 KT 60 MPH
$$
Forecaster Roberts
488
WTNT44 KNHC 100914 CCA
TCDAT4
Hurricane Isaac Discussion Number 11...Corrected
NWS National Hurricane Center Miami FL AL092018
500 AM AST Mon Sep 10 2018
Corrected intensity forecast in table below.
Isaac has generally changed little during the past several hours.
The small hurricane continues to have a central dense overcast
feature with some fragmented bands to the south of the center. The
Dvorak classifications remain 4.0/65 kt from both TAFB and SAB, and
therefore, the initial intensity is held at 65 kt.
Isaac is moving westward at 11 kt. The models remain in poor
agreement this cycle as they are split into two camps. The UKMET,
HWRF, and a few other models show Isaac recurving near or to the
east of the Lesser Antilles toward a developing trough over the
central Atlantic. Conversely, the GFS and ECMWF have been very
consistent in showing a due westward motion across the Lesser
Antilles and into the Caribbean as the cyclone moves on the south
side of a strengthening mid-level ridge. The NHC track forecast
continues to favor the usually more reliable GFS and ECMWF models,
and this forecast is near a blend of those aids. It should be
noted, however, that confidence in this track forecast is low given
the model spread.
The intensity forecast is also quite uncertain. One of the complex
factors is Isaac's compact size as small hurricanes like this one
are more prone to quick intensity changes, both up and down. In
addition, the intensity guidance is in poor agreement as solutions
range from steady weakening from this point onward to the HWRF that
shows Isaac becoming a major hurricane. Given that the wind shear
is expected to remain less than 10 kt for another day or two,
strengthening is forecast during that time period. After that,
however, an increase in shear first from a trough over the central
Atlantic and later from the outflow from Florence should result in
weakening when the system moves across the Lesser Antilles and into
the Caribbean Sea. The NHC intensity forecast is not too different
from the previous one and lies above the model consensus in the
short term, but below it at the later forecast times. This
forecast is in best agreement with the latest LGEM guidance.
Key Messages:
1. Isaac is a small hurricane and uncertainty in the forecast is
higher than normal. Although Isaac is forecast to begin weakening
when it approaches the Lesser Antilles, it is still expected to be
at or near hurricane intensity when it reaches the islands.
2. Interests in the Lesser Antilles should continue to monitor Isaac
during the next few days.
FORECAST POSITIONS AND MAX WINDS
INIT 10/0900Z 14.7N 42.7W 65 KT 75 MPH
12H 10/1800Z 14.8N 44.6W 70 KT 80 MPH
24H 11/0600Z 15.0N 47.4W 75 KT 85 MPH
36H 11/1800Z 15.0N 50.3W 80 KT 90 MPH
48H 12/0600Z 15.0N 53.0W 80 KT 90 MPH
72H 13/0600Z 15.3N 58.0W 70 KT 80 MPH
96H 14/0600Z 15.5N 64.0W 60 KT 70 MPH
120H 15/0600Z 15.6N 69.2W 50 KT 60 MPH
$$
Forecaster Cangialosi
73 de Scott KF5JRV
Pmail: KF5JRV@KF5JRV.#NWAR.AR.USA.NA
email: KF5JRV@ICLOUD.COM
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