663
WTNT45 KNHC 212032
TCDAT5

Hurricane Erin Discussion Number 42
NWS National Hurricane Center Miami FL AL052025
500 PM AST Thu Aug 21 2025

Erin is gradually pulling away from the U.S., but coastal flooding
and tropical storm conditions continue across portions of the North
Carolina and Virginia coastline. A pair of ASCAT passes from a few
hours ago confirmed Erin's large size with its associated
tropical-storm-force winds extending nearly 500 n mi across. In
fact, comparing Erin with other systems around the same intensity
and in similar locations over the past couple of decades indicates
that it is around the 90th percentile in size. Overall, the
structure of the system has changed little since the aircraft
departed earlier today, and based on that data and the satellite
intensity estimates, the initial intensity is held at 85 kt. Erin is
producing very rough seas, and the associated swells are covering
nearly the entire western Atlantic from the Bahamas to Atlantic
Canada.

Erin has turned northeastward, and it is currently moving at 050/17
kt. A faster motion to the northeast or east-northeast is expected
within the mid-latitude westerlies over the next few days, taking
Erin out to sea over the north Atlantic. The models are in good
agreement, and only minor changes were made to the previous NHC
forecast.

The environmental conditions are expected to become increasingly
hostile around Erin, as southwesterly vertical wind shear is likely
to steadily increase while humidity values and sea surface
temperatures decrease. This should result in weakening, but Erin
will likely only slowly lose strength due to its large size. Erin
is expected to cross the north wall of the Gulf Stream in a couple
of days, and that should help lead to its extratropical transition.
The NHC intensity forecast is similar to the previous one, and
follows HCCA and IVCN in the short term, but leans toward the global
model guidance during the predicted extratropical phase.

KEY MESSAGES:

1. Erin will continue to produce life-threatening surf and rip
currents along the beaches of the Bahamas, much of the east coast of
the U.S., Bermuda, and Atlantic Canada during the next several days.
Beachgoers in those areas should follow advice from lifeguards,
local authorities, and beach warning flags.

2. Storm surge flooding will continue on the North Carolina Outer
Banks through tonight. The storm surge will be accompanied by large
waves, leading to significant beach erosion and overwash, making
some roads impassible.

3. Tropical storm conditions are expected for a few more hours
along portions of the northeast North Carolina and Virginia coast.
Wind gusts to tropical storm force are likely along portions of the
remainder of the U.S. Mid-Atlantic and southern New England coasts
today through early Friday.

4. Tropical storm conditions are expected on Bermuda this
evening through early Friday. Gusts to gale force are possible
along the coast of Nova Scotia on Friday and the Avalon Peninsula of Newfoundland on Saturday.


FORECAST POSITIONS AND MAX WINDS

INIT 21/2100Z 36.4N 69.1W 85 KT 100 MPH
12H 22/0600Z 38.0N 66.2W 80 KT 90 MPH
24H 22/1800Z 40.0N 61.3W 75 KT 85 MPH
36H 23/0600Z 41.8N 55.3W 75 KT 85 MPH
48H 23/1800Z 44.7N 47.3W 70 KT 80 MPH...POST-TROP/EXTRATROP
60H 24/0600Z 47.9N 39.0W 65 KT 75 MPH...POST-TROP/EXTRATROP
72H 24/1800Z 50.9N 31.8W 60 KT 70 MPH...POST-TROP/EXTRATROP
96H 25/1800Z 55.8N 22.4W 50 KT 60 MPH...POST-TROP/EXTRATROP
120H 26/1800Z 56.9N 20.5W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi


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