[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 042056
TCDAT1

Tropical Storm Earl Discussion Number   8
NWS National Hurricane Center Miami FL       AL062022
500 PM AST Sun Sep 04 2022

The large bursting pattern that was observed this morning with Earl
has evolved more into a shear pattern this afternoon, with the
low-level center becoming partially exposed to the west of the
coldest cloud tops that are displaced about 50 n mi east of the
center. An Air Force Reconnaissance aircraft conducted an
afternoon mission through the storm and found the highest 850 mb
flight-level winds of 51 kt with SFMR winds up to 48 kt. Satellite
intensity estimates remain unchanged from this morning, and the
initial intensity will remain 45 kt for this advisory.

The last several fixes from the aircraft indicate Earl has resumed a
slow northwestward motion at 310/4 kt. The forecasting reasoning has
not changed much from the previous forecast cycle, as a mid-level
ridge is expected to result in Earl turning to the north-northwest
over the next 12 to 24 hours. This slow motion should continue
thereafter as the ridge continues to slowly break down and shift
gradually eastward through the early part of this week. Towards the
end of the forecast, the strongest ridging is expected to be east of
Earl, allowing the cyclone to slowly recurve to the north-northeast.
The latest track guidance this cycle has narrowed somewhat, with the
latest ECMWF forecast shifting east, while the most recent GFS
shifted a touch west. Thus, little change was made to the NHC track
forecast this advisory, which lies quite close to the latest TVCN
and HCCA consensus aids.

It appears that this morning's convective burst was unsuccessful in
helping to vertically align Earl's vortex, and the mid-level center
noted on Puerto Rico radar is still located east of the aircraft
fixes. This failure was likely due to continued westerly vertical
wind shear undercutting the outflow layer and importing dry air into
Earl's core. However, most of the global and regional hurricane
models suggest that additional convective bursts will continue over
the next 24-48 hours, resulting in gradual intensification as the
cyclone becomes better vertically aligned. Thus, the latest NHC
intensity forecast continues to show slow intensification in the
short-term, with Earl possibly attaining hurricane intensity in a
couple of days. After 72 hours, both the GFS and ECMWF suggest the
shear will decrease, while the cyclone may also undergo a favorable
trough interaction. The guidance responds to this pattern by
indicating more significant intensification, and the latest advisory
shows a somewhat higher peak intensity of 105 kt by day 5.

While tropical-storm-force winds are still forecast to stay north of
the northern Leeward Islands, the Virgin Islands, and Puerto Rico,
training rain-bands are producing heavy rainfall over these islands.
Users should refer to products issued by local weather offices in
these areas.


KEY MESSAGES:

1.  Heavy rainfall from Earl is expected to lead to limited flash,
urban, and small stream flooding impacts over the Leeward Islands,
U.S. and British Virgin Islands, and Puerto Rico today. Rapid rises
on rivers and mudslides in areas of steep terrain are possible in
Puerto Rico. Locally considerable flood impacts cannot be ruled out
in areas that receive heavier rainfall totals.

2.  Earl is forecast to pass to the north of the the Virgin Islands
and Puerto Rico tonight, but gusty winds, especially in squalls,
remain possible on those islands overnight.


FORECAST POSITIONS AND MAX WINDS

INIT  04/2100Z 20.0N  65.2W   45 KT  50 MPH
 12H  05/0600Z 21.1N  65.2W   50 KT  60 MPH
 24H  05/1800Z 22.3N  65.4W   55 KT  65 MPH
 36H  06/0600Z 23.5N  65.5W   60 KT  70 MPH
 48H  06/1800Z 24.6N  65.6W   65 KT  75 MPH
 60H  07/0600Z 25.4N  65.5W   70 KT  80 MPH
 72H  07/1800Z 26.4N  65.1W   75 KT  85 MPH
 96H  08/1800Z 28.2N  64.0W   85 KT 100 MPH
120H  09/1800Z 31.4N  61.5W  105 KT 120 MPH

$$
Forecaster Papin
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