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Tropical Storm Henri Discussion Number  22
NWS National Hurricane Center Miami FL       AL082021
500 AM EDT Sat Aug 21 2021
 
An earlier GMI satellite microwave image continued to indicate that
Henri's low-level center was still located near the northwestern 
edge of the convective canopy.  However, more recent geostationary 
satellite imagery shows that the convection is beginning to wrap 
around the northeastern and eastern portions of the circulation 
suggesting that the anticipated decrease in shear is occuring, and 
that Henri may be on the verge of strengthening.  The latest 
subjective satellite intensity estimates from SAB and TAFB remained 
unchanged so the initial intensity remains 60 kt, in agreement with 
those estimates and the earlier aircraft data.  The next 
reconnaissance aircraft mission should be in the storm around 
1200 UTC this morning.
 
Henri is moving north-northeastward or 015/10 kt. A mid- to
upper-level low and associated trough over the Appalachians and
Ohio Valley should steer Henri north-northeastward at a faster
forward speed today.  As Henri moves around the eastern portion of
the upper-low, the storm is forecast to turn north-northwestward
tonight.  This motion will bring the center of Henri near or over
portions of Long Island and Southern New England on Sunday and into
the northeastern United States Sunday night.  After that time, the
cyclone should turn east-northeastward as it becomes caught in the
mid-latitude westerlies.  The latest dynamical model envelope
continues to narrow for the first 24 to 36 hours of the forecast
period and only small adjustments were needed to that portion of
the track.  After that time, the guidance has trended to taking
Henri farther inland over the Northeastern United States, and the
NHC forecast as been modified accordingly.
 
Decreasing shear, upper-level divergence associated with the trough
to Henri's west, and warm SSTs should allow the cyclone to
strengthen during the next 12-18 hours.  Although not explicitly
shown in the intensity forecast, Henri could still peak around 75 kt
later today or this evening.  After that time, cooler waters are
likely to cause a gradual reduction in intensity, however, Henri is
forecast to be at or near hurricane strength at landfall. Once the
center moves inland over the Northeast United States, a faster rate
of filling is anticipated.  The system is forecast to become
post-tropical in about 60 hours, and it will likely dissipate around
day 4, if not a little sooner.  The updated intensity forecast is
near the upper-end of the intensity guidance during the first 12-24
hours, and is close to the Decay-SHIPS model thereafter.
 
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 is expected to begin late
tonight or Sunday in portions of Long Island, Connecticut,
Rhode Island, and southeastern Massachusetts, where a Storm Surge
Warning has been issued. Dangerous storm surge is possible
beginning late tonight or Sunday in western portions of Long
Island and Connecticut in the Storm Surge Watch area.  Residents in
these areas should follow any advice given by local officials.
 
2. Hurricane conditions are expected to begin late tonight or
Sunday in portions of Long Island and Connecticut, where a
Hurricane Warning has been issued.  Hurricane conditions are
possible late tonight or Sunday across portions of Rhode Island.
 
3. Heavy rainfall may lead to considerable flash, urban, and small
stream flooding, along with the potential for widespread minor and
isolated moderate river flooding, over portions of Long Island, New
England, southeast New York and northern New Jersey.
 
4. Swells from Henri will continue to affect much of the east coast
of the U.S. through the weekend. These swells could cause
life-threatening surf and rip currents.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0900Z 33.1N  73.2W   60 KT  70 MPH
 12H  21/1800Z 35.6N  72.3W   70 KT  80 MPH
 24H  22/0600Z 38.8N  72.0W   70 KT  80 MPH
 36H  22/1800Z 40.9N  72.7W   60 KT  70 MPH...INLAND
 48H  23/0600Z 42.1N  73.6W   35 KT  40 MPH...INLAND
 60H  23/1800Z 42.8N  73.3W   25 KT  30 MPH...POST-TROP/INLAND
 72H  24/0600Z 43.3N  71.5W   25 KT  30 MPH...POST-TROP/INLAND
 96H  25/0600Z 44.5N  62.5W   25 KT  30 MPH...POST-TROPICAL
120H  26/0600Z...DISSIPATED
 
$$
Forecaster Brown
 
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