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Tropical Storm Henri Discussion Number  15
NWS National Hurricane Center Miami FL       AL082021
1100 AM EDT Thu Aug 19 2021
 
Henri is not as well organized as it was yesterday.  Microwave 
images show that the vortex is titled to the south with height due 
to about 25 kt of north-northeasterly wind shear.  The system is 
still producing a fair amount of deep convection, however, and the 
cloud pattern resembles a central dense overcast with banding 
features limited to the south side of the circulation.  The Dvorak 
estimates continue to range from 55 kt to 65 kt, and therefore, the 
initial intensity is again held at 60 kt.  The Air Force Reserve 
Hurricane Hunters will be investigating Henri later today, and the 
data the aircraft collects will be very helpful in assessing the 
storm's structure and strength.
 
The tropical storm is moving just south of due west at 9 kt.  Henri 
is expected to move generally westward through tonight as the storm 
remains on the south side of a mid-level ridge.  On Friday, however, 
a trough is expected to cut off over the Ohio Valley and 
mid-Atlantic region of the U.S. while a ridge amplifies to the east 
of Henri over the western Atlantic.  A combination of these features 
should cause Henri to turn northward on Friday and accelerate in 
that direction over the weekend.  By early next week, the ridge 
is expected to weaken, which should cause Henri to turn more 
toward the east.  The models are in much better agreement than they 
were yesterday and their solutions are clustering around southern 
New England on Sunday and Monday. The NHC track forecast is just a 
tad to the left of the previous one and lies near the typically 
best-performing models, the various consensus aids. In addition 
to the Air Force aircraft that flies through the storm, the NOAA 
Gulfstream IV jet will also be flying around Henri later today to 
help assess the environmental conditions and gather data for the 
numerical models. It is hoped that these data will help the models 
more accurately predict the future track of the storm.

The current north-northeasterly shear over Henri is forecast to 
continue for about another day, and given the degraded structure of 
the system it seems unlikely that the storm will strengthen during 
that time period.  However, the shear is expected to decrease on 
Friday and it will remain quite low through the weekend.  
Therefore, strengthening to a hurricane is expected during that 
time period.  Once Henri crosses the north wall of the Gulf Stream 
in a few days, steady weakening is predicted.  The NHC intensity 
forecast is just an update of the previous one and lies near the 
middle of the guidance envelope.

It should be noted that as Henri gains latitude and moves near 
New England, the wind field is expected to expand.  Therefore, 
users are reminded to not focus on the exact forecast points as 
impacts will extend far from the center. 
 
Key Messages:
 
1. Henri is forecast to be near the northeast coast of the U.S.
on Sunday and Monday, and the risks of storm surge, wind, and rain 
impacts in portions of southern New England and eastern Long Island 
are increasing.  Watches will likely be required for portions of 
this area on Friday.  
 
2. 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  19/1500Z 29.5N  70.5W   60 KT  70 MPH
 12H  20/0000Z 29.7N  71.9W   60 KT  70 MPH
 24H  20/1200Z 30.4N  72.9W   60 KT  70 MPH
 36H  21/0000Z 31.9N  72.9W   65 KT  75 MPH
 48H  21/1200Z 34.4N  72.0W   75 KT  85 MPH
 60H  22/0000Z 37.3N  70.7W   80 KT  90 MPH
 72H  22/1200Z 39.6N  70.0W   75 KT  85 MPH
 96H  23/1200Z 41.6N  69.7W   55 KT  65 MPH
120H  24/1200Z 42.3N  67.0W   45 KT  50 MPH
 
$$
Forecaster Cangialosi
 
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