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Tropical Storm Henri Discussion Number   8
NWS National Hurricane Center Miami FL       AL082021
500 PM AST Tue Aug 17 2021
 
Henri appears to be gaining strength.  Satellite images show banding 
features becoming increasingly curved, especially on the east side 
of the system, and an eye feature has been occasionally seen in 
radar images from Bermuda.  The upper-level outflow is also well 
established to the north and east of the center.  The center itself 
is estimated to be located near the western edge of the convection, 
but it is possible that a new center is forming farther east.  The 
initial intensity is raised to 55 kt following the Dvorak 
classification from TAFB.  The initial wind radii has been expanded 
outward based on an earlier ASCAT pass.
 
The tropical storm appears to have slowed down, and the latest
initial motion estimate is 255/2 kt.  A subtropical ridge over the
western Atlantic is building eastward to the north of Henri, and
this feature should steer the storm westward at a slightly faster
pace during the next two to three days.  After that time, the ridge
is expected to weaken and shift farther east as a cut off low or
negatively-tilted trough develops over the northeast U.S.  This
change in the steering pattern should cause Henri to turn
northeastward between Bermuda and the east coast of the U.S in the
72-120 h period.  There is a fair amount of spread in exactly when
and where Henri makes this turn and the GFS and EC ensembles have
some members not far offshore of New England and Atlantic Canada.
Overall, the guidance has shifted westward again this cycle, and the
NHC track forecast has been adjusted accordingly from days 3 to 5.
 
The northwesterly shear currently affecting Henri is subsiding, 
which should allow the storm to gain a little more strength tonight. 
However, a round of moderate northerly shear is expected to setup 
over Henri on Wednesday and Thursday and that will likely 
temporarily end the opportunity for strengthening.  Although this 
shear would typically cause some weakening, the combination of warm 
SSTs and increasing mid-level moisture could offset the negative 
influences of the shear.  By Friday and over the weekend, the shear 
is expected to lessen again and since the other environmental 
factors are predicted to remain favorable for the storm, 
strengthening is shown from days 3-5.  This forecast is above the 
previous one, and lies fairly close to the middle of the guidance 
envelope.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/2100Z 30.4N  64.2W   55 KT  65 MPH
 12H  18/0600Z 30.3N  65.5W   60 KT  70 MPH
 24H  18/1800Z 30.2N  67.0W   60 KT  70 MPH
 36H  19/0600Z 30.2N  68.6W   60 KT  70 MPH
 48H  19/1800Z 30.3N  70.0W   60 KT  70 MPH
 60H  20/0600Z 31.0N  71.1W   60 KT  70 MPH
 72H  20/1800Z 32.0N  71.5W   65 KT  75 MPH
 96H  21/1800Z 35.5N  69.6W   70 KT  80 MPH
120H  22/1800Z 39.1N  65.2W   70 KT  80 MPH
 
$$
Forecaster Cangialosi
 
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