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Tropical Storm Henri Discussion Number  19
NWS National Hurricane Center Miami FL       AL082021
1100 AM EDT Fri Aug 20 2021
 
The Air Force Reserve Hurricane Hunters investigated Henri this 
morning and based on the flight-level, SFMR, and dropsonde data, the 
initial intensity is still around 55 kt.  The minimum pressure has 
also been relatively steady.  The low-level center of Henri is 
located close to the northwestern edge of the main area of deep 
convection, and the vortex is still not vertically aligned due to 
20-25 kt of northerly vertical wind shear.  Although the intensity 
of Henri has not changed much during the past couple of days, 
satellite images show an improving cloud pattern with well- 
established outflow in the eastern semicircle, which could indicate 
that Henri is poised to strengthen.
 
There is some uncertainty in the exact position of Henri given the 
recent aircraft fixes and the tilt of the vortex, but the initial 
motion appears to be northwestward at 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 turn northward 
tonight and accelerate in that direction on Saturday. Some of the 
models show a slight bend to the west around the time Henri is 
forecast to make landfall on Sunday, and there remains a fair amount 
spread in the guidance in where the center of Henri will come 
ashore.  The latest GFS and ECMWF ensemble members span a region 
from near New York City to Cape Cod for the landfall point.  Based 
on the latest consensus aids and initial position, the official 
track forecast is nudged to the west of the previous one and shows 
landfall occurring by late Sunday.  After day 3, Henri is forecast 
to eject northeastward across the Gulf of Maine.
 
The ongoing northerly shear is expected to decrease later today, and 
the global models show a favorable upper-level wind pattern 
developing over the storm later today 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 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 in 
3 to 4 days, and the new forecast shows Henri dissipated by day 5, 
in agreement with most of the global models.
 
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 and hurricane conditions are 
possible beginning Sunday in portions of Long Island, Connecticut, 
Rhode Island, and southeastern Massachusetts, where a Storm Surge 
Watch and Hurricane Watch are in effect. Residents in these areas 
should follow any advice given by local officials. 

2. Heavy rainfall may lead to flash, urban, and small stream 
flooding, along with the potential for widespread minor and isolated 
moderate river flooding, over portions of southern New England 
Sunday into Monday. 

3. Swells from Henri will begin to reach much of the east coast of 
the U.S. and Atlantic Canada by the end of the week and continue 
through the weekend. These swells could cause life-threatening surf 
and rip currents.

FORECAST POSITIONS AND MAX WINDS
 
INIT  20/1500Z 30.4N  73.7W   55 KT  65 MPH
 12H  21/0000Z 31.5N  73.7W   60 KT  70 MPH
 24H  21/1200Z 34.1N  72.7W   70 KT  80 MPH
 36H  22/0000Z 37.3N  71.8W   75 KT  85 MPH
 48H  22/1200Z 39.8N  71.7W   65 KT  75 MPH
 60H  23/0000Z 41.4N  71.8W   60 KT  70 MPH...INLAND
 72H  23/1200Z 42.4N  71.8W   40 KT  45 MPH...INLAND
 96H  24/1200Z 43.7N  69.4W   35 KT  40 MPH...POST-TROPICAL
120H  25/1200Z...DISSIPATED
 
$$
Forecaster Cangialosi
 
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