Tropical Report

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Sat Sep 15 2018

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Florence, located inland over extreme eastern South Carolina,
on Tropical Storm Helene, located about 200 miles west-southwest of
the western Azores, and on Tropical Storm Joyce, located about
950 miles west-southwest of the Azores. The National Hurricane
Center has issued the last advisory on former Tropical Storm Isaac,
which has dissipated over the central Caribbean Sea.

1. A broad area of low pressure could form near Bermuda early next
week. Additional development, if any, is expected to be slow while
the system moves little.
* Formation chance through 48 hours…low…near 0 percent.
* Formation chance through 5 days…low…10 percent.

Forecaster Beven

NOAA HURRICANE HUNTER PLANE INDICATES ISAAC HAS DISSIPATED… …THIS IS THE LAST ADVISORY

Remnants Of Isaac Discussion Number 31
NWS National Hurricane Center Miami FL AL092018
500 AM EDT Sat Sep 15 2018

A NOAA Hurricane Hunter aircraft investigated Isaac over the past
few hours and was unable to identify a well-defined center. The
plane found multiple small and poorly-defined circulations embedded
within a larger area of weak and variable winds, well to the south
of the previous estimated center location. The plane also found that
the minimum pressure has risen to around 1006 mb. All of this data
confirmed what two late-arriving ASCAT overpasses from earlier this
evening indicated, that Isaac has opened up into a southwest to
northeast oriented trough. Since Isaac does not have a well-defined
center, it no longer meets the NHC definition of a tropical cyclone
and this is the last advisory.

The strongest SFMR winds found by the plane were around 30 kt,
mainly to the north of the deep convection, so the intensity has
been set at that value. Although some of the regional hurricane
models suggest that small short-lived circulations like the ones
found by the plane could temporarily spin up within the larger
envelope of the tropical wave over the next several days, none of
the dynamical models currently show any significant redevelopment of
Isaac. The wave will likely continue westward across the Caribbean
Sea over the next few days, producing gusty winds and occasional
heavy rains over portions of Hispaniola and Jamaica.

This is the last public advisory issued by the National Hurricane
Center on Isaac. Additional information can be found in High Seas
Forecasts issued by the National Weather Service, under AWIPS header
NFDHSFAT1, WMO header FZNT01 KWBC, and available online at
https://ocean.weather.gov/shtml/NFDHSFAT1.shtml.

FORECAST POSITIONS AND MAX WINDS

INIT 15/0900Z 14.8N 70.8W 30 KT 35 MPH
12H 15/1800Z…DISSIPATED

$$
Forecaster Zelinsky

HELENE CONTINUES TO APPROACH THE AZORES… …EXPECTED TO PRODUCE TROPICAL-STORM-FORCE WINDS AND HEAVY RAINS

Tropical Storm Helene Discussion Number 32
NWS National Hurricane Center Miami FL AL082018
500 AM AST Sat Sep 15 2018

Helene appears to be maintaining its strength. Recent microwave
images show that the storm has an eye feature, but the vortex is
significantly tilted in the vertical due to southwesterly shear.
Deep convection is most organized in bands to the north and west of
the center. Based on the tropical storm’s appearance in microwave
images, the initial intensity is again held at 60 kt, near the high
end of the satellite intensity estimates. Helene is expected to
gradually weaken during the next few days due to the influences of
southwesterly shear, drier air, and much cooler SSTs along the
forecast track. These conditions should also cause Helene to lose
tropical characteristics, and the storm is forecast become
extratropical in 24 to 36 hours.

The tropical storm is moving north-northeastward at a fairly fast
pace, 19 kt. The center of Helene is expected to pass to the west
of the Azores by tonight. However, Helene has a fairly large wind
field, and tropical-storm-force winds are expected across the
western Azores as the storm passes by. A shortwave trough to the
northwest of the system is expected to approach Helene by tonight,
and that should cause the cyclone to turn northeastward and then
speed up in that direction as it heads toward Ireland and the United
Kingdom late this weekend and early next week. The models are in
fair agreement, and only small changes were made to the previous NHC
track forecast.

Helene is expected to be a post-tropical cyclone when it approaches
Ireland and the United Kingdom in two to three days. Interests in
those locations should consult products from their local
meteorological service for information about potential impacts from
Helene. Local forecasts and warnings for the UK can be found on the
website of the UK Met Office at https://www.metoffice.gov.uk/.
Local forecasts and warnings for Ireland can be found on the website
of Met Eireann at https://www.met.ie/.

FORECAST POSITIONS AND MAX WINDS

INIT 15/0900Z 37.7N 34.8W 60 KT 70 MPH
12H 15/1800Z 39.7N 32.7W 60 KT 70 MPH
24H 16/0600Z 41.8N 29.2W 55 KT 65 MPH
36H 16/1800Z 44.1N 24.3W 55 KT 65 MPH…POST-TROP/EXTRATROP
48H 17/0600Z 46.7N 18.1W 55 KT 65 MPH…POST-TROP/EXTRATROP
72H 18/0600Z 55.8N 5.0W 50 KT 60 MPH…POST-TROP/EXTRATROP
96H 19/0600Z…DISSIPATED

$$
Forecaster Cangialosi

FLORENCE MOVING SLOWLY ACROSS EASTERN SOUTH CAROLINA… …CONTINUES TO PRODUCE CATASTROPHIC FLOODING OVER NORTH CAROLINA AND SOUTH CAROLINA

Tropical Storm Florence Discussion Number 64
NWS National Hurricane Center Miami FL AL062018
500 AM EDT Sat Sep 15 2018

Florence is slowly weakening while its center remains inland over
extreme eastern South Carolina. However, WSR-88D Doppler radar
still shows some intense bands of convection over the eastern
portion of the circulation, and these bands have been training over
the coast of North Carolina overnight. Based on current Doppler
velocities of 55-60 kt at around 5500 ft, the current intensity is
set at 45 kt. The system should continue to weaken as it moves
farther inland today, and it is anticipated that Florence will
become a tropical depression tonight. The official intensity
forecast is similar to the Decay-SHIPS model guidance through
around day 3. By days 4 and 5, the post-tropical cyclone is
forecast to strengthen somewhat due to baroclinic processes after
moving off the New England coast and passing near southern Atlantic
Canada.

Radar and satellite fixes indicate that Florence continues its
west-southwestward motion at around 255/4 kt. A mid-level high
pressure area to the northwest of Florence is forecast to shift to
the north, northeast, and east of the cyclone over the next couple
of days. As a result, Florence should turn northwestward and
northward, and then north-northeastward through 72 hours. Late
in the forecast period, the system is expected to accelerate
east-northeastward in the mid-latitude westerlies. The official
forecast is somewhat faster than the previous one at days 4 and 5
but is in good agreement with the latest global model runs.

Although coastal storm surge flooding will gradually subside
today, extremely heavy rainfall will continue to be a serious
hazard associated with slow-moving Florence. More than a foot of
rain has already fallen across portions of southeastern North
Carolina, and more rain is still to come, which will cause
disastrous flooding that will spread inland through the weekend.

Key Messages:

1. Life-threatening storm surge will continue along portions of
the North Carolina coast through today, and also along the Neuse
and Pamlico Rivers in western Pamlico Sound, where rainfall and
freshwater flooding will also contribute to high water levels.
Dangerous storm surge could also affect portions of the northeast
coast of South Carolina coast today.

2. Life-threatening, catastrophic flash floods and prolonged
significant river flooding are likely over portions of the
Carolinas and the southern to central Appalachians from western
North Carolina into west-central Virginia and far eastern West
Virginia through early next week, as Florence moves slowly inland.
In addition to the flash flood and flooding threat, landslides are
also possible in the higher terrain of the southern and central
Appalachians across western North Carolina into southwest Virginia.

3. Tropical storm conditions will continue along the coast within
the tropical storm warning area and also well inland across portions
of South Carolina and North Carolina today.

4. Large swells affecting Bermuda, portions of the U.S. East Coast,
and the northwestern and central Bahamas will continue this week,
resulting in life-threatening surf and rip currents.

FORECAST POSITIONS AND MAX WINDS

INIT 15/0900Z 33.6N 79.5W 45 KT 50 MPH
12H 15/1800Z 33.6N 80.2W 40 KT 45 MPH…INLAND
24H 16/0600Z 33.9N 81.3W 30 KT 35 MPH…INLAND
36H 16/1800Z 35.1N 82.4W 25 KT 30 MPH…INLAND
48H 17/0600Z 37.0N 83.5W 25 KT 30 MPH…INLAND
72H 18/0600Z 40.5N 80.0W 20 KT 25 MPH…POST-TROP/REMNT LOW
96H 19/0600Z 43.5N 68.0W 30 KT 35 MPH…POST-TROP/EXTRATROP
120H 20/0600Z 47.0N 54.0W 40 KT 45 MPH…POST-TROP/EXTRATROP

$$
Forecaster Pasch

JOYCE MOVING EASTWARD WITH NO CHANGE IN STRENGTH.

Tropical Storm Joyce Discussion Number 11
NWS National Hurricane Center Miami FL AL102018
500 AM AST Sat Sep 15 2018

There has not much change with Joyce overnight. The tropical storm
is producing a fair amount of deep convection to the north and west
of the center, but there are some dry slots on the east side. A
blend of the latest satellite intensity estimates supports holding
the initial wind speed at 45 kt. Joyce is currently just east of an
upper-level trough and the flow aloft is quite diffluent near the
cyclone. This upper-level pattern could allow Joyce to strengthen
slightly today. However, by tonight, southwesterly flow aloft is
expected to increase over the cyclone. This increase in shear
combined with decreasing mid-level humidities and cooling SSTs
should lead to a steady weakening trend after 12 hours. The cyclone
is forecast to dissipate in 3 to 4 days, but some of the models
suggest that this could occur sooner.

The tropical storm is moving eastward at 7 kt. Joyce is embedded
in the same trough as Helene and it should follow that tropical
cyclone east-northeastward to northeastward at increasing forward
speeds during the next day or two. Beyond that time, if there
is anything left of Joyce, the system will likely turn back to the
east or east-southeast as it moves within the mid-latitude
westerlies. The models are in fairly good agreement, and this
forecast lies close to the middle of the guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT 15/0900Z 31.9N 42.2W 45 KT 50 MPH
12H 15/1800Z 32.7N 40.6W 50 KT 60 MPH
24H 16/0600Z 33.9N 37.8W 45 KT 50 MPH
36H 16/1800Z 34.6N 34.1W 40 KT 45 MPH
48H 17/0600Z 34.7N 31.0W 35 KT 40 MPH
72H 18/0600Z 33.0N 26.5W 30 KT 35 MPH
96H 19/0600Z…DISSIPATED

$$
Forecaster Cangialosi

There are no tropical cyclones in the Eastern North Pacific at this time