Tropical Storm HENRI Advisory mié, 18-08

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Tropical Storm Henri Discussion Number  10
NWS National Hurricane Center Miami FL       AL082021
500 AM AST Wed Aug 18 2021

There's been little change in Henri's satellite appearance this
morning. The surface center is still located just to the northwest
of a gradually expanding central dense overcast, and there still
appears to be an eye-like feature in the Bermuda Doppler radar
presentation.  However, there are no indications in the GOES-16
BD-curve enhanced infrared images of a developing warm spot.
Subjective and objective satellite intensity estimates remain
steady, and the initial intensity is held at 55 kt for this
advisory.

Although the surrounding thermodynamic environment is ripe for
further significant development, moderate northwesterly shear
continues to impinge on the cyclone causing difficulty in inner-core
convective development. Consequently, little change in strength is
expected during the next couple days, and in fact the statistical
SHIPS model indicates an increase in a more northerly shear
component on Thursday.  By Saturday afternoon, however, the shear
should decrease as the cyclone slides beneath an upper ridge axis
off of the southeast U.S. coast.  Henri is expected to further
intensity through the remaining period as the upper-wind flow
becomes much more diffluent.  The official intensity forecast is
similar to the previous advisory, and lies between the SHIPS model
and the HFIP Corrected Consensus Approach aid after the 60-hour
period.

The initial motion is estimated to be westward, or 260/7 kt.  A high
amplitude mid- to upper-level anticyclone situated north-northeast
of Henri should steer the cyclone toward the west during the next 36
hours, or so.  Thereafter, the aforementioned ridge is forecast to
weaken and shift eastward in response to a mid-latitude shortwave
trough moving over the northeastern U.S.  As a result of the change
in the synoptic steering pattern, Henri should turn toward the
northwest, north, and then northeast through the remaining portion
of the forecast. With so much uncertainty or spread in the global
and regional models beyond day 3, the best approach at this point is
to base the NHC forecast on the better performing multi-model
consensus guidance, which has once again shifted a bit to the left
of the previous track forecast.  I think it's worth noting that the
GFSv16 model is now showing a shortwave ridge building over
eastern Canada on Sunday, which causes Henri to move more northward
toward the New England coast.  Therefore, additional changes or
shifts of the track beyond the 60-hour period may be required on
subsequent advisories.

Due to the increased uncertainty in the track forecast, interests
along the New England coast should monitor the progress of Henri.


FORECAST POSITIONS AND MAX WINDS

INIT  18/0900Z 30.1N  65.7W   55 KT  65 MPH
 12H  18/1800Z 29.9N  66.9W   60 KT  70 MPH
 24H  19/0600Z 29.8N  68.7W   60 KT  70 MPH
 36H  19/1800Z 29.8N  70.6W   60 KT  70 MPH
 48H  20/0600Z 30.4N  71.8W   60 KT  70 MPH
 60H  20/1800Z 31.4N  72.3W   65 KT  75 MPH
 72H  21/0600Z 33.0N  71.9W   70 KT  80 MPH
 96H  22/0600Z 37.6N  69.0W   75 KT  85 MPH
120H  23/0600Z 40.5N  66.1W   65 KT  75 MPH

$$
Forecaster Roberts