[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 051456
TCDAT1

Tropical Storm Earl Discussion Number  11
NWS National Hurricane Center Miami FL       AL062022
1100 AM AST Mon Sep 05 2022

Earl is attempting to restructure again this morning. Convection,
which had been primarily located east of the center, due to
persistent moderate westerly vertical wind shear, has begun to pivot
up-shear into the northern quadrant of the storm. A NOAA-P3 mission
that was in the storm this morning indicated the low-level wind
field in the northern semicircle of the storm had also intensified,
with several dropsondes indicating boundary layer mean winds in the
55-65 kt range and one reported a surface wind gust of 57 kt. These
values match the twin Doppler radar (TDR) onboard of the aircraft,
with peak 0.5 km winds above 64 kt. The peak SFMR winds from the
mission were 58 kt, with 700-mb flight-level winds at 63 kt. The
satellite presentation this morning though remains somewhat ragged,
with the low-level circulation partially exposed, though TDR
analysis suggest the vertical tilt between the low- and mid-level
centers has decreased compared to yesterday. Based partially on the
these aircraft observations, the intensity has been set at 55 kt for
this advisory, which also agrees with the latest TAFB intensity
estimate.

The center of the cyclone may have relocated a bit northeast of the
previous position, but the mean general motion appears to still be
to the north-northwest at 340/4 kt. The track model guidance is
generally in good agreement in the short-term that this slow
northward motion should continue, as the cyclone moves poleward
through a weakness in the deep-layer ridging to its north. This
mid-level ridge is then forecast to continue breaking down as a
deep-layer trough approaches from the eastern United States. This
synoptic pattern change should be enough for Earl to begin a
somewhat faster north-northeastward motion after 72 hours. However,
after this time, uncertainty in the along-track direction between
both deterministic and ensemble guidance starts to increase
dramatically, with the GFS and its ensemble mean faster, and the
ECWMF and its ensemble mean slower. The latest NHC track forecast is
a bit further to the east early on, due to the adjustment in the
initial position, but ends up near, if a bit slower, than the
previous forecast track by the end of the forecast period. This
track is close to an average of the latest GFS and ECMWF forecasts.
Given the large uncertainty observed in the guidance at day 5,
forecast track confidence in that time frame is lower than normal.

While Earl was found to be a bit stronger by the NOAA-P3 aircraft
this morning, westerly vertical wind shear is still quite evident,
and both the GFS- and ECMWF-based SHIPS guidance suggests this shear
could actually increase a bit more over the next 24-36 hours. Thus,
only a slight additional amount of intensification is forecast
today, followed by Earl remaining steady over the 24-36 hour period.
After the cyclone moves poleward of the shear zone induced by a
nearby tropical upper-tropospheric trough, the shear is expected to
decrease significantly, allowing more robust intensification. The
tropical storm wind field is also forecast to increase dramatically
during this period as a result of the system also undergoing a
positive upper-level trough interaction. The latest NHC intensity
forecast still shows a peak intensity of 105 kt by day 5, though
some regional hurricane models (HWRF, COAMPS-TC) are a bit higher
than this forecast.

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.  Considerable flood impacts cannot be ruled out in
areas that receive heavier rainfall totals.

2.  Currently Earl is forecast to track to the southeast of Bermuda.
However, the wind field of the tropical cyclone is expected to
increase significantly, and interests on the island should continue
to monitor the progress of the storm closely.


FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z 21.5N  65.3W   55 KT  65 MPH
 12H  06/0000Z 22.5N  65.3W   60 KT  70 MPH
 24H  06/1200Z 23.7N  65.5W   60 KT  70 MPH
 36H  07/0000Z 24.7N  65.6W   60 KT  70 MPH
 48H  07/1200Z 25.9N  65.6W   65 KT  75 MPH
 60H  08/0000Z 27.0N  65.3W   70 KT  80 MPH
 72H  08/1200Z 28.3N  64.8W   80 KT  90 MPH
 96H  09/1200Z 31.3N  62.8W   95 KT 110 MPH
120H  10/1200Z 34.4N  59.1W  105 KT 120 MPH

$$
Forecaster Papin
This weather bulletin was brought to you by:
www.nashvilleweather.net