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Tropical Storm Henri Discussion Number  12
NWS National Hurricane Center Miami FL       AL082021
500 PM AST Wed Aug 18 2021
 
Henri appears a little better organized this afternoon.  The storm 
still has a central dense overcast pattern and there have been hints 
of an eye evident in visible satellite images. Microwave images 
continue to show a mid-level eye feature, but the storm does not 
appear quite as well organized in the low-levels, and the vortex is 
still titled southward with height. The latest Dvorak estimates 
range from 55 to 67 kt, and based on that data the initial 
intensity is nudged up to 60 kt, just below hurricane strength.
 
Henri is moving just south of due west at a slightly faster pace 
now, 265/8 kt.  The storm is expected to continue westward for 
another 36 hours or so as it moves in the flow on the south side of 
a mid-level ridge.  A gradual turn to the north is forecast to begin 
on Friday when a cutoff low forms over the Ohio Valley and the 
northeastern U.S.  This general northward motion should continue 
through the weekend as another ridge builds to the east of Henri 
over the northwestern Atlantic. The models continue their westward 
shift, and the NHC track forecast has again been adjusted in that 
direction and no longer shows a northeastward motion out to sea.  In 
particular, the westward adjustment at day 5 was a sizable 150 
miles, and even with this shift the NHC forecast is still a little 
to the east of some of the consensus aids. NOAA Gulfstream IV 
missions and special weather balloon soundings have been scheduled, 
and it is hoped that this additional data will help the models 
handle the evolving steering pattern.  Given the uncertainty in the 
longer range track forecast, users should be prepared for additional 
adjustments to the NHC track prediction in future forecast cycles.
 
The storm is currently in an environment of about 15-20 kt of 
northerly wind shear according to the SHIPS model and analyses from 
CIMSS at the University of Wisconsin, which is the reason the vortex 
is currently titled.  The shear should persist for another day or 
so, and little change in strength seems likely during that time 
period.  However, strengthening is expected on Friday and Saturday 
as the shear decreases while the storm remains over the Gulf Stream. 
Some weakening seems likely at days 4 and 5 when the storm is 
expected to be over cooler waters.  The NHC intensity forecast lies 
roughly near the middle of the guidance envelope and only minor 
changes were made to the previous prediction.
 
Key Messages:
 
1. The forecast track of Henri has shifted toward the northeast 
coast of the U.S. this weekend and early next week, increasing the 
risk of direct storm surge, wind, and rain impacts in portions of 
the northeastern U.S. and Atlantic Canada during that time. 
Interests in these areas should closely follow the progress of 
Henri and check for updates to the forecast. 

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  18/2100Z 29.9N  67.6W   60 KT  70 MPH
 12H  19/0600Z 29.8N  69.0W   60 KT  70 MPH
 24H  19/1800Z 29.8N  70.7W   60 KT  70 MPH
 36H  20/0600Z 30.1N  72.3W   65 KT  75 MPH
 48H  20/1800Z 31.0N  73.2W   70 KT  80 MPH
 60H  21/0600Z 32.7N  72.7W   75 KT  85 MPH
 72H  21/1800Z 35.2N  71.7W   80 KT  90 MPH
 96H  22/1800Z 39.3N  70.0W   70 KT  80 MPH
120H  23/1800Z 41.4N  69.8W   60 KT  70 MPH
 
$$
Forecaster Cangialosi
 
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