[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 160235
TCDAT1

Tropical Storm Josephine Discussion Number  18
NWS National Hurricane Center Miami FL       AL112020
1100 PM AST Sat Aug 15 2020

An Air Force Reserve reconnaissance aircraft investigating
Josephine this evening manages to find a barely close low-level
circulation center that was displaced about 90 nmi to the west of
the edge of the southernmost burst of deep convection. Maximum
flight-level and surface were likely missed since the aircraft did
not fly through the strongest convection. Thus, the intensity is
being maintained at 40 kt based on continuity and a blend of
subjective and objective satellite classifications.

The initial motion is west-northwestward or an uncertain 300/13 kt.
Due to Josephine's severely sheared state, the system could open up
into a sharp tropical wave at any time during the next 36 hours,
which complicates determining a forecast track. For now, it will be
assumed that there will be some identifiable low-level vorticity
feature that will serve as a proxy center for Josephine or its
remnants, which are forecast to continue to move west-northwestward
along the southwestern periphery of a deep-layer subtropical ridge.
Thereafter, the cyclone is expected to recurve to the north and
north-northeast through a break in the ridge that is forecast to
develop southwest of Bermuda in 48 hours or so, with at least the
remnants passing near Bermuda in about 120 hours. The NHC official
forecast track lies close to the previous advisory track and the
tightly-clustered simple- and corrected-consensus models.

Josephine is expected to remain in an environment of moderate to
strong westerly shear for at least the next 48-60 h, followed by
sharply decreasing shear conditions thereafter.  For the next two
days or so, however, Josephine is forecast to weaken owing to the
strong shear conditions and surrounding dry mid-level air, with the
possibility of the tropical storm degenerating into an open wave at
any time. If the remnant vorticity can manage to remain intact
through a deep enough layer of the troposphere, then some
regeneration could occur in the 72-120 hour time when the vertical
shear/mid-level moisture are forecast to decrease/increase
significantly. However, it still remains unclear at this time
whether there will be enough remnant circulation to take advantage
of those more favorable conditions.


KEY MESSAGES:

1. Josephine is passing far enough to the northeast of the Leeward
Islands to prevent major impacts.  However, interests there should
continue to monitor its progress until the storm has passed north
of that area.

2. Locally heavy rainfall is possible in the northern Leeward
Islands, the Virgin Islands, and Puerto Rico as Josephine passes by
to the northeast. Isolated minor flooding is possible in Puerto
Rico through Monday.


FORECAST POSITIONS AND MAX WINDS

INIT  16/0300Z 20.1N  62.6W   40 KT  45 MPH
 12H  16/1200Z 21.0N  64.3W   35 KT  40 MPH
 24H  17/0000Z 22.3N  66.3W   35 KT  40 MPH
 36H  17/1200Z 23.7N  67.9W   30 KT  35 MPH
 48H  18/0000Z 25.1N  68.8W   30 KT  35 MPH
 60H  18/1200Z 27.1N  68.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  19/0000Z 29.0N  68.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  20/0000Z 30.6N  67.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  21/0000Z 32.8N  64.1W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Stewart
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