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KF5JRV > WX 04.10.18 13:26l 226 Lines 9976 Bytes #999 (0) @ NA
BID : 21085_KF5JRV
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Subj: NWS NHC Atlantic WX - Sept 11
Path: IZ3LSV<IQ2LB<IK1NHL<CX2SA<HG8LXL<XE1FH<N9PMO<AB0AF<KF5JRV
Sent: 180911/1122Z 21085@KF5JRV.#NWAR.AR.USA.NA BPQ6.0.16
510
WTNT41 KNHC 110856
TCDAT1
Hurricane Florence Discussion Number 48
NWS National Hurricane Center Miami FL AL062018
500 AM AST Tue Sep 11 2018
Recent satellite imagery shows that the eye of Florence has become
cloud filled and an earlier 0441 UTC microwave overpass revealed a
double eyewall structure. These observations suggest that an
eyewall replacement cycle is likely underway. Subjective and
objective Dvorak current intensity numbers have not changed
so the initial intensity will remain 120 kt for this advisory.
An Air Force Reserve Hurricane Hunter mission is en route to the
storm and should provide a better assessment of Florence's
structure and intensity this morning. NOAA buoy 41049 located
about 80 nmi north of the eye, has reported tropical-storm-force
winds during the last several hours and seas as high as 23 ft.
Florence's upper-level environment is predicted to remain quite
favorable while the storm traverses sea surface temperatures of
around 29C over the next 48 hours. Additional strengthening is
forecast during this time, but some fluctuations in intensity are
likely due to eyewall replacement cycles. The updated NHC intensity
forecast once again calls for additional intensification and brings
Florence to near category 5 strength within the next 24 to 36
hours. After 48 hours, a slight increase in southwesterly
shear could result in some weakening, but Florence is expected to
remain an extremely dangerous hurricane when it approaches the U.S.
coastline.
Florence has accelerated as anticipated and is now moving
west-northwestward or 290 degrees at 13 kt. The track forecast
reasoning has not changed much. A mid-level ridge to the northeast
of Bermuda is expected steer Florence quickly west-northwestward to
northwestward toward the southeast United States coast over the next
2 to 3 days. By 72 hours, a high pressure ridge building over the
Upper-Midwest and Great Lakes regions is forecast to cause a
significant reduction in Florence's forward speed and the hurricane
is predicted to meander over the eastern portions of North or South
Carolina at days 4 and 5. The ECMWF has trended slower this cycle
at days 4 and 5, and as a result the NHC forecast shows slightly
less motion at those time periods. The spread in the guidance
increases by 72 hours, with the GFS and its ensemble mean along the
right side of the guidance, while the ECMWF remains along the left
edge. It should be noted that there are still a number of ECMWF
members that are even farther left. The NHC track forecast has been
nudged to the left and is close to the TVCN consensus aid. Given the
amount of uncertainty by day 3, 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. Storm Surge and Hurricane
watches have been issued for a portion of the coast of South and
North Carolina. Additional watches may be required later today.
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 has been issued for a portion of this area.
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
has been issued for a part of this area. 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 11/0900Z 26.4N 64.1W 120 KT 140 MPH
12H 11/1800Z 27.2N 66.4W 125 KT 145 MPH
24H 12/0600Z 28.7N 69.4W 130 KT 150 MPH
36H 12/1800Z 30.5N 72.2W 130 KT 150 MPH
48H 13/0600Z 32.2N 74.5W 125 KT 145 MPH
72H 14/0600Z 34.3N 77.1W 115 KT 130 MPH
96H 15/0600Z 35.2N 78.0W 45 KT 50 MPH...INLAND
120H 16/0600Z 36.0N 79.0W 25 KT 30 MPH...INLAND
$$
Forecaster Brown
592
WTNT43 KNHC 110833
TCDAT3
Hurricane Helene Discussion Number 16
NWS National Hurricane Center Miami FL AL082018
500 AM AST Tue Sep 11 2018
An Advanced Microwave Technology Sounder (ATMS) 165GHZ overpass on
Helene indicated a well-developed closed eyewall and a deep
convective outer band with associated cold cloud tops of -76C
wrapping around the south through east quadrants of the cyclone.
The initial intensity is held at 95 kt for this advisory and is
based on a blend of the subjective and objective T-numbers.
There still appears to be a small window of opportunity for Helene
to strengthen, during the next 12 hours or so, before the ocean and
the upper wind environment become less conducive. Afterward, the
SSTs decrease significantly and the vertical shear increases, which
should induce gradual weakening. By day 3, the sea surface
temperatures increase, however, the southwesterly shear persists and
the mid-level atmospheric moisture decreases. Interestingly
enough, the global models show Helene either maintaining tropical
storm strength or even intensifying by the end of the period,
possibly due to some mid-latitude dynamic forcing influences. It's
also worth noting that the Florida State Cyclone Phase Evolution
analysis and forecast product shows the system retaining a
relatively symmetric warm core through the entire forecast.
The initial motion is estimated to be west-northwestward, or 300/12
kt. A turn more toward the northwest is forecast early on
Wednesday. Beyond mid-period, the large-scale models agree that a
mid- to upper tropospheric trough over the northeast Atlantic will
dig southward inducing a weakness in the eastern portion of the
subtropical ridge. In response to this change in the synoptic
steering pattern, Helene should slowly turn northward and then
north-northeastward during the next 72 to 96 hours, followed by a
turn toward the northeast on day 5. The official forecast is close
to the previous one, and lies near the TVCN consensus model and the
GFS ensemble mean.
FORECAST POSITIONS AND MAX WINDS
INIT 11/0900Z 16.0N 33.6W 95 KT 110 MPH
12H 11/1800Z 16.8N 35.0W 100 KT 115 MPH
24H 12/0600Z 18.0N 36.5W 85 KT 100 MPH
36H 12/1800Z 19.5N 37.6W 75 KT 85 MPH
48H 13/0600Z 21.4N 38.3W 65 KT 75 MPH
72H 14/0600Z 25.7N 38.8W 55 KT 65 MPH
96H 15/0600Z 31.4N 36.6W 50 KT 60 MPH
120H 16/0600Z 37.3N 31.2W 50 KT 60 MPH
$$
Forecaster Roberts
608
WTNT44 KNHC 110831
TCDAT4
Tropical Storm Isaac Discussion Number 15
NWS National Hurricane Center Miami FL AL092018
500 AM AST Tue Sep 11 2018
Isaac has not changed much overnight. Satellite images indicate
that the strong tropical storm still has a central dense overcast
pattern and a limited amount of outer bands. Earlier microwave
data indicated that the center was not located in the middle of the
convection, however, likely due to some westerly shear. Since
the cyclone has changed little during the past several hours, the
initial intensity is held at 60 kt, which is an average of the TAFB
and SAB Dvorak final T- and CI-numbers. A nearby NOAA buoy shows
that the wind field of Isaac is very compact, with tropical-storm-
force winds only extending up to 40 n mi from the center.
Satellite fixes suggest that Isaac continues to move westward at 13
kt. Although there remains a fair amount of spread in the models,
the usually more reliable GFS and ECMWF models continue to show a
westward motion during the next several days as the storm moves on
the south side of a strengthening mid-level ridge. The NHC track
forecast continues to follow that theme, and this forecast lies
near a blend of the GFS and ECMWF aids. This forecast is a little
slower than the previous one, and takes Isaac across the Lesser
Antilles and into the eastern Caribbean in 2 to 3 days.
Predicting Isaac's intensity has been challenging. Isaac appeared
to have been in relatively favorable conditions during the past day
or so, but it did not strengthen. The upper-level pattern should
remain relatively favorable for another day, so modest strengthening
back to a hurricane is possible during that time. Thereafter,
however, an increase in shear first from a trough in the central
Atlantic and then from the outflow of Florence should cause some
weakening when the storm moves into the Caribbean. The models
are in a little better agreement this cycle as the HWRF is no
longer showing Isaac becoming a major hurricane. The NHC intensity
forecast is very similar to the previous one and is fairly close to
the consensus aids.
Key Messages:
1. Isaac is expected to be at or near hurricane intensity when it
approaches the Lesser Antilles. However, confidence in the forecast
is lower than normal.
2. Interests in the Lesser Antilles should continue to monitor
Isaac during the next couple of days. Watches will likely be
required for portions of the Lesser Antilles later today.
FORECAST POSITIONS AND MAX WINDS
INIT 11/0900Z 14.6N 48.1W 60 KT 70 MPH
12H 11/1800Z 14.6N 50.1W 60 KT 70 MPH
24H 12/0600Z 14.6N 52.6W 65 KT 75 MPH
36H 12/1800Z 14.8N 55.0W 65 KT 75 MPH
48H 13/0600Z 15.1N 57.6W 60 KT 70 MPH
72H 14/0600Z 15.5N 62.8W 55 KT 65 MPH
96H 15/0600Z 15.6N 67.4W 55 KT 65 MPH
120H 16/0600Z 15.8N 72.0W 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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