239 
WTNT45 KNHC 170259
TCDAT5
 
Hurricane Erin Discussion Number  23
NWS National Hurricane Center Miami FL       AL052025
1100 PM AST Sat Aug 16 2025
 
After rapidly intensifying for the first part of the day, Erin now
appears to be in the middle stages of an eyewall replacement cycle
(ERC). Both the NOAA and Air Force Reserve reconnaissance have
indicated concentric eyewalls on their missions this evening, and in
response, the inner eyewall is starting to become more degraded with
decreasing winds. With that said, there is not an especially well
defined secondary wind maximum quite yet, primarily only observed in
the NOAA-P3 Tail Doppler Radar data in the northeastern quadrant.
The peak flight level winds reported by the NOAA and Air Force
aircraft were both 130 kt at 700 mb. The initial intensity is
therefore reduced to 120 kt for this advisory, and this could be
generous.
 
The inner eyewall of Erin has been wobbling around, likely due to
some trochoidal motion as it interacts with the building secondary
wind maximum, but the longer-term motion is around 290/12 kt. Erin
has moved left of the NHC forecast track over the past day, and I
suspect some of this left-of expected motion could be due to the
small inner-core size of the hurricane, which was poorly resolved by
all of the hurricane-regional forecast models. However, as the
overall wind field of Erin grows in size, a more consistent
west-northwestward motion is expected to resume tonight and persist
over the next 12-24 hours. After that time, a series of shortwave
troughs will move offshore of Atlantic Canada, helping to reinforce
a longwave trough over the north-central portion of the Atlantic.
This should create a growing weakness to the north of Erin,
ultimately allowing the large hurricane to turn northward and then
northeastward by the end of the forecast period. The track guidance
this cycle made another westward adjustment, and the NHC track
forecast was nudged in that direction. The current track remains to
the east of both the HCCA and ECMWF track aids, so it would not be
surprising to see some additional leftward adjustments in subsequent
forecast cycles.
 
The future intensity is probably the most challenging aspect of
Erin's forecast. Erin's maximum sustained winds have been decreasing
as a secondary eyewall gradually becomes better defined. A little
more weakening could occur in the short term as these structural
changes occur. However, none of the hurricane-regional models
appears to have a good handle on Erin's current structure (they all
have a much broader core). Given that the vertical wind shear is
currently low, and the hurricane is well embedded in a moist
environment, this ERC is expected to complete without much issue,
though it will likely take a bit of time for the hurricane's maximum
sustained winds to recover as its wind field broadens. Thus, the NHC
intensity forecast shows some reintensification in the 24 h period
after this ERC completes. Afterwards, it wouldn't be surprising to
see another cycle begin, and at 36-48 h northwesterly shear is still
anticipated to increase some. Their combination should begin a
weakening trend with Erin as it continues to grow in size. The NHC
intensity forecast is a little lower than the previous advisory,
primarily due to the weaker initial intensity, but is still roughly
in line with the intensity consensus aids.
 
A recent scatterometer pass indicates that Erin's outer-core is
growing in size, and the models remain in strong agreement that the
system will grow further the next several days. In fact, by the
middle of next week, Erin is forecast to at least double or triple
in size, which will result in rough ocean conditions over the
western Atlantic.
 
 
KEY MESSAGES:
 
1. Heavy rainfall at times through Sunday across the northern
Leeward Islands, the Virgin Islands, and Puerto Rico may lead to
locally considerable flash and urban flooding, along with landslides
or mudslides.
 
2. Tropical-storm conditions are possible in the Turks and Caicos
Islands during the next 48 h, where a Tropical Storm Watch is in
effect. Gusts to tropical storm force in Erin's outer rainbands are
likely in portions of the Virgin Islands and Puerto Rico through
Sunday. Tropical-storm force wind gusts are possible in the
Southeast Bahamas beginning late Sunday.
 
3. Erin is expected to produce life-threatening surf and rip
currents along the beaches of the Bahamas, much of the east coast of
the U.S., and Atlantic Canada next week.
 
4.  Interests in Bermuda should continue to monitor the progress of
Erin since there is a risk of strong winds, heavy rainfall, and high
surf by the middle part of next week.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/0300Z 20.3N  65.1W  120 KT 140 MPH
 12H  17/1200Z 20.8N  66.7W  115 KT 130 MPH
 24H  18/0000Z 22.0N  68.5W  130 KT 150 MPH
 36H  18/1200Z 23.3N  69.9W  120 KT 140 MPH
 48H  19/0000Z 24.5N  70.8W  115 KT 130 MPH
 60H  19/1200Z 26.0N  71.5W  110 KT 125 MPH
 72H  20/0000Z 28.0N  72.1W  105 KT 120 MPH
 96H  21/0000Z 32.0N  71.5W  100 KT 115 MPH
120H  22/0000Z 37.5N  65.5W   90 KT 105 MPH
 
$$
Forecaster Papin