[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 300838
TCDAT3

Hurricane Lorenzo Discussion Number  32
NWS National Hurricane Center Miami FL       AL132019
500 AM AST Mon Sep 30 2019

The satellite presentation of Lorenzo has generally changed little
during the last several hours.  The hurricane continues to maintain
a well-defined inner core with a ragged cloud-filled eye.  The
outer bands are well established to the north and east of the
center, but are restricted on the south side of the circulation due
to some southwesterly shear and drier air being wrapped into that
portion of the cyclone.  The initial intensity estimate is set at 90
kt based on T5.0/90 kt Dvorak classifications from TAFB and SAB.

Lorenzo is moving north-northeastward at 11 kt through a break in
the Atlantic subtropical ridge.  The models generally agree that
Lorenzo should pick up forward speed and move northeastward
during the next day or two as a trough amplifies over the central
Atlantic.  This flow should take the core of Lorenzo near or to
the west of the western Azores late Tuesday and early Wednesday.
After that time, the spread in the guidance increases with several
of the models including the GFS, HWRF, and HMON showing Lorenzo
turning north-northeastward or northward as it moves around
the east side of a large extratropical low.  The new ECMWF run has
shifted closer to the GFS/HWRF/HMON solutions, but it still is
considerably to the east of those models as it shows less
interaction with the extratropical low.  The NHC track forecast has
been adjusted a little to the left to come into better agreement
with the latest consensus aids.  Although the spread in the models
is not as large as it was yesterday, the forecast beyond 48 hours is
still of low confidence given the uncertainty in the longer-term
steering flow.

The intensity forecast appears to be more straightforward than the
track forecast.  The bulk of the guidance shows the hurricane
maintaining its intensity or weakening slightly during the next day
or two while it remains over relatively warm waters and in moderate
wind shear conditions.  It seems likely that Lorenzo will
be a significant hurricane when it passes near the Azores in about
2 days.  After that time, more notable weakening should occur due to
a significant drop off in SSTs, drier air, and much stronger shear.
In fact, these conditions should ultimately lead to extratropical
transition, which is expected to be complete by 72 hours.
Dissipation is now predicted to occur by day 5 following the global
model guidance.

Key Messages:

1.  Lorenzo is a large and powerful hurricane, and its hurricane-
and tropical-storm-force wind fields are expected to expand further
during the next few days.  Hurricane and Tropical Storm Watches
are in effect for the Azores, and Hurricane and Tropical Storm
Warnings could be required later today for those islands.

2.  Large swells generated by Lorenzo will continue to spread across
much of the north Atlantic basin during the next few days.  These
swells will produce life-threatening surf and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT  30/0900Z 28.7N  43.1W   90 KT 105 MPH
 12H  30/1800Z 30.3N  42.3W   85 KT 100 MPH
 24H  01/0600Z 32.7N  40.3W   85 KT 100 MPH
 36H  01/1800Z 36.0N  36.6W   85 KT 100 MPH
 48H  02/0600Z 40.5N  31.0W   80 KT  90 MPH
 72H  03/0600Z 52.0N  20.0W   65 KT  75 MPH...POST-TROP/EXTRATROP
 96H  04/0600Z 57.0N  13.5W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  05/0600Z...DISSIPATED

$$
Forecaster Cangialosi
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