[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 290235
TCDAT3

Hurricane Lorenzo Discussion Number  27
NWS National Hurricane Center Miami FL       AL132019
1100 PM AST Sat Sep 28 2019

Lorenzo has rapidly strengthened this evening.  An eyewall
replacement cycle completed earlier today, with a recent SSMIS
microwave overpass showing that a new eyewall about 30 n mi in
diameter now completely encircles the eye.  The cold cloud tops
surrounding the eye have expanded, with a solid ring of temperatures
measuring colder than minus 70 degrees Celsius.  In addition, the
eye has cleared, with satellite derived cloud-top temperatures now
above 15 degrees Celsius.  Throughout the evening, the objective and
subjective intensity estimates have climbed, with 0130 UTC special
classifications from TAFB and SAB as well as a recent UW-CIMSS ADT
estimate unanimously agreeing on a 140-kt initial intensity.  This
makes Lorenzo an extremely dangerous category 5 hurricane.

The initial motion is now northward at 9 kt.  Lorenzo will be
steered north through a break between two subtropical ridges through
tonight, with a turn to the north-northeast expected on Sunday.
After Sunday, Lorenzo will begin to get caught up in increasing
southwesterly flow ahead of an approaching mid-latitude trough. This
will cause the cyclone to accelerate northeastward through the end
of the forecast period.  The official track forecast is essentially
an update of the previous one, and is near the middle of the
consensus aids.

Lorenzo will likely peak in intensity overnight as it remains in the
current favorable environment.  Some fluctuations in intensity are
possible on Sunday mainly due to eyewall replacement cycles.  By
Sunday night, Lorenzo will begin to feel the effects of some
southwesterly shear ahead of the approaching trough, while it also
moves over waters of lower oceanic heat content.  These factors
should induce a steady weakening trend through 48 hours.  After that
time, SSTs below 26 C should cause a faster weakening trend.  By 72
hours, the cyclone will begin interacting with the approaching
trough and an associated cold front, which will begin a transition
to an extratropical low.  This transition is forecast to complete by
120 hours, but it could happen a little sooner than that.  The
official forecast was increased through the first 48 hours due to
the increase in initial intensity, and then blends to near the
previous official forecast by 72 hours.

With this latest advisory intensity, Lorenzo becomes the strongest
hurricane in history this far north and east in the Atlantic basin.


Key Messages:

1.  Lorenzo is a large hurricane, and its hurricane- and
tropical-storm-force wind fields are expected to expand further
during the next several days.  Regardless of Lorenzo's exact track
near the Azores, strong winds are becoming increasingly likely on
the islands Tuesday night and Wednesday, and residents there should
monitor the progress of the hurricane.

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


FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 24.2N  44.9W  140 KT 160 MPH
 12H  29/1200Z 25.5N  44.7W  135 KT 155 MPH
 24H  30/0000Z 27.1N  44.1W  125 KT 145 MPH
 36H  30/1200Z 28.8N  43.3W  115 KT 130 MPH
 48H  01/0000Z 30.8N  42.0W  105 KT 120 MPH
 72H  02/0000Z 36.7N  35.3W   95 KT 110 MPH
 96H  03/0000Z 45.0N  23.5W   75 KT  85 MPH
120H  04/0000Z 52.2N  10.7W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Latto
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