Hurricane Ernesto Discussion Number  20
NWS National Hurricane Center Miami FL       AL052024
1100 AM AST Fri Aug 16 2024

Ernesto appears to be feeling the effects of vertical wind shear 
this morning. The structure on satellite has become more asymmetric 
with the coldest cloud tops shifted to the east of the center fixes 
being made by an ongoing Air Force Hurricane Hunter mission, which 
also found a 50-mile-wide eye open to the southwest. Despite the 
degraded satellite appearance, the aircraft still found 700-mb 
flight-level winds up to 98 kt, with peak SFMR-derived winds of 76 
kt in the southeast quadrant of Ernesto. A blend of these data 
still supports an intensity of 85 kt this advisory, though this 
could be generous. The hurricane remains quite large with 
tropical-storm-force winds extending up to 240 n mi southeast of the 
center.

Ernesto continues to move north-northeast, estimated at 330/12 kt. 
The deep-layer trough that has been initially influencing Ernesto's 
motion is already starting to leave the tropical cyclone behind, and 
the track guidance indicates the hurricane will begin to slow its 
forward motion over the next day or so while continuing to move 
north-northeastward. After that time, another shortwave trough 
currently over the upper Midwest U.S. is forecast to dig 
southeastward, which should ultimately result in Ernesto 
accelerating northeastward around the periphery of the subtropical 
ridge to its southeast. The track guidance this cycle is quite close 
to the prior forecast, and the NHC track forecast only has minor 
changes compared to the previous cycle.

Vertical wind shear diagnosed by SHIPS guidance is already up to 25 
kt or greater, and this shear is likely to persist for another 12 to 
24 h. Thus the latest NHC intensity forecast now shows a little more 
weakening, though it should be noted some of the hurricane regional 
models show Ernesto weakening below hurricane intensity over the 
next 36 h.  Thereafter, as the first trough bypasses the system, the 
forecast shear decreases while the tropical cyclone remains over 28 
C or warmer sea surface temperatures. Thus, there remains an 
opportunity for Ernesto to re-intensify before it reaches the north 
wall of the Gulf Stream by early next week.  However, extratropical 
transition will likely be underway shortly after it crosses over 
much cooler waters after 72 h, with the latest NHC forecast showing 
the system becoming extratropical at 96 h.


Key Messages:

1. Ernesto is expected to bring a prolonged period of strong winds
and storm surge on Bermuda starting this afternoon through Saturday
night. A hurricane warning is in effect for the island, and
preparations to protect life and property should be rushed to
completion.

2. Heavy rainfall associated with Ernesto is expected to impact
Bermuda through this weekend and will likely result in considerable
life-threatening flash flooding, especially in low-lying areas on
the island.

3. Even though Ernesto is forecast to remain well offshore the U.S.
East Coast, swells generated by the hurricane are expected to affect
the area through the weekend.  Beach goers should be aware of a
significant risk of life-threatening surf and rip currents, and stay
out of the water if advised by lifeguards.  Surf and rip currents
are also possible on the Turks and Caicos, the Bahamas, Bermuda,
and Atlantic Canada during the next few days.


FORECAST POSITIONS AND MAX WINDS

INIT  16/1500Z 29.5N  66.4W   85 KT 100 MPH
12H  17/0000Z 31.0N  65.5W   80 KT  90 MPH
24H  17/1200Z 32.5N  64.9W   75 KT  85 MPH
36H  18/0000Z 33.8N  64.5W   70 KT  80 MPH
48H  18/1200Z 35.4N  63.9W   70 KT  80 MPH
60H  19/0000Z 38.1N  62.5W   75 KT  85 MPH
72H  19/1200Z 41.6N  59.7W   80 KT  90 MPH
96H  20/1200Z 48.4N  47.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  21/1200Z 52.0N  26.0W   40 KT  45 MPH...POST-TROP/EXTRATROP

$$
Forecaster Papin