599
WTNT43 KNHC 202042
TCDAT3
Tropical Storm Henri Discussion Number 20
NWS National Hurricane Center Miami FL AL082021
500 PM EDT Fri Aug 20 2021
Henri appears to be slowly gaining strength. Deep convection has
been increasing during the past few hours and the upper-level
outflow continues to become better established on the east side of
the circulation. However, the low-level center is still located
near the northwestern edge of the deep convection due to ongoing
northerly wind shear. An ASCAT-B pass from a few hours ago showed
peak winds of around 55 kt, with the strongest winds on the
southeast side of the circulation. Based on this data, the initial
intensity is set at 60 kt. An Air Force Reserve Hurricane Hunter
aircraft is scheduled to investigate Henri again this evening and
the data the plane collects will be very helpful in estimating the
storm's strength and structure.
The tropical storm appears to be making the advertised turn to the
right, with the latest initial motion estimated to be 335/6 kt. A
trough over the central Appalachians is expected to cut off tonight,
and the combination of that feature and a building ridge to the
east/northeast of Henri should cause the storm to accelerate to the
north on Saturday. The latest model runs have generally trended to
the left again and are a bit faster, with most showing landfall in
about 48 hours. Most of the models now show a slight left turn
before landfall as Henri gets caught in the circulation of the
aforementioned trough. The latest GFS and ECMWF ensemble members
continue to span a region from near New York City to Cape Cod for
the landfall point. Based on the latest consensus aids, the
official track forecast has again been nudged to the west of the
previous one and shows landfall occurring on Sunday. After day 3,
Henri is forecast to eject northeastward.
The ongoing northerly shear is expected to decrease tonight, and
the global models show a favorable upper-level wind pattern
developing over the storm through the weekend. These more
conducive atmospheric conditions combined with the warm Gulf
Stream waters should allow Henri to strengthen to a hurricane
tonight or early Saturday, with additional intensification expected
into Saturday night. By early Sunday, however, Henri is forecast to
cross the north wall of the Gulf Stream, and that should end its
opportunity for strengthening. Although steady to rapid weakening is
forecast while Henri moves over cooler waters south of Long
Island and New England, it will likely still be at or very near
hurricane intensity when it reaches the coast. Post-tropical
transition is forecast to occur by day 3 and the system should
dissipate in 4 or 5 days.
Users are reminded to not focus on the exact forecast of the
center of Henri since impacts will extend far from the center.
Key Messages:
1. Dangerous storm surge inundation is expected to begin Sunday in
portions of Long Island, Connecticut, Rhode Island, and
southeastern Massachusetts, where a Storm Surge Warning has been
issued. Dangerous storm surge is possible beginning Sunday in
western portions of Long Island and Connecticut in the Storm Surge
Watch area. Residents in these areas should follow any advice given
by local officials.
2. Hurricane conditions are expected to begin Sunday in portions
of Long Island and Connecticut, where a Hurricane Warning has been
issued. Hurricane conditions are possible Sunday across portions
of Rhode Island and southeastern Massachusetts.
3. Heavy rainfall may lead to considerable flash, urban, and small
stream flooding, along with the potential for widespread minor and
isolated moderate river flooding, over portions of Long Island and
New England Sunday into Monday.
4. Swells from Henri will continue to affect much of the east coast
of the U.S. through the weekend. These swells could cause
life-threatening surf and rip currents.
FORECAST POSITIONS AND MAX WINDS
INIT 20/2100Z 31.2N 73.9W 60 KT 70 MPH
12H 21/0600Z 32.8N 73.3W 65 KT 75 MPH
24H 21/1800Z 35.8N 72.3W 75 KT 85 MPH
36H 22/0600Z 38.9N 71.9W 75 KT 85 MPH
48H 22/1800Z 40.8N 72.4W 65 KT 75 MPH
60H 23/0600Z 42.0N 72.8W 45 KT 50 MPH...INLAND
72H 23/1800Z 42.9N 72.6W 30 KT 35 MPH...POST-TROPICAL
96H 24/1800Z 43.8N 68.9W 25 KT 30 MPH...POST-TROPICAL
120H 25/1800Z...DISSIPATED
$$
Forecaster Cangialosi
WTNT43 KNHC 202042
TCDAT3
Tropical Storm Henri Discussion Number 20
NWS National Hurricane Center Miami FL AL082021
500 PM EDT Fri Aug 20 2021
Henri appears to be slowly gaining strength. Deep convection has
been increasing during the past few hours and the upper-level
outflow continues to become better established on the east side of
the circulation. However, the low-level center is still located
near the northwestern edge of the deep convection due to ongoing
northerly wind shear. An ASCAT-B pass from a few hours ago showed
peak winds of around 55 kt, with the strongest winds on the
southeast side of the circulation. Based on this data, the initial
intensity is set at 60 kt. An Air Force Reserve Hurricane Hunter
aircraft is scheduled to investigate Henri again this evening and
the data the plane collects will be very helpful in estimating the
storm's strength and structure.
The tropical storm appears to be making the advertised turn to the
right, with the latest initial motion estimated to be 335/6 kt. A
trough over the central Appalachians is expected to cut off tonight,
and the combination of that feature and a building ridge to the
east/northeast of Henri should cause the storm to accelerate to the
north on Saturday. The latest model runs have generally trended to
the left again and are a bit faster, with most showing landfall in
about 48 hours. Most of the models now show a slight left turn
before landfall as Henri gets caught in the circulation of the
aforementioned trough. The latest GFS and ECMWF ensemble members
continue to span a region from near New York City to Cape Cod for
the landfall point. Based on the latest consensus aids, the
official track forecast has again been nudged to the west of the
previous one and shows landfall occurring on Sunday. After day 3,
Henri is forecast to eject northeastward.
The ongoing northerly shear is expected to decrease tonight, and
the global models show a favorable upper-level wind pattern
developing over the storm through the weekend. These more
conducive atmospheric conditions combined with the warm Gulf
Stream waters should allow Henri to strengthen to a hurricane
tonight or early Saturday, with additional intensification expected
into Saturday night. By early Sunday, however, Henri is forecast to
cross the north wall of the Gulf Stream, and that should end its
opportunity for strengthening. Although steady to rapid weakening is
forecast while Henri moves over cooler waters south of Long
Island and New England, it will likely still be at or very near
hurricane intensity when it reaches the coast. Post-tropical
transition is forecast to occur by day 3 and the system should
dissipate in 4 or 5 days.
Users are reminded to not focus on the exact forecast of the
center of Henri since impacts will extend far from the center.
Key Messages:
1. Dangerous storm surge inundation is expected to begin Sunday in
portions of Long Island, Connecticut, Rhode Island, and
southeastern Massachusetts, where a Storm Surge Warning has been
issued. Dangerous storm surge is possible beginning Sunday in
western portions of Long Island and Connecticut in the Storm Surge
Watch area. Residents in these areas should follow any advice given
by local officials.
2. Hurricane conditions are expected to begin Sunday in portions
of Long Island and Connecticut, where a Hurricane Warning has been
issued. Hurricane conditions are possible Sunday across portions
of Rhode Island and southeastern Massachusetts.
3. Heavy rainfall may lead to considerable flash, urban, and small
stream flooding, along with the potential for widespread minor and
isolated moderate river flooding, over portions of Long Island and
New England Sunday into Monday.
4. Swells from Henri will continue to affect much of the east coast
of the U.S. through the weekend. These swells could cause
life-threatening surf and rip currents.
FORECAST POSITIONS AND MAX WINDS
INIT 20/2100Z 31.2N 73.9W 60 KT 70 MPH
12H 21/0600Z 32.8N 73.3W 65 KT 75 MPH
24H 21/1800Z 35.8N 72.3W 75 KT 85 MPH
36H 22/0600Z 38.9N 71.9W 75 KT 85 MPH
48H 22/1800Z 40.8N 72.4W 65 KT 75 MPH
60H 23/0600Z 42.0N 72.8W 45 KT 50 MPH...INLAND
72H 23/1800Z 42.9N 72.6W 30 KT 35 MPH...POST-TROPICAL
96H 24/1800Z 43.8N 68.9W 25 KT 30 MPH...POST-TROPICAL
120H 25/1800Z...DISSIPATED
$$
Forecaster Cangialosi
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