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Hurricane Lorenzo Discussion Number  21
NWS National Hurricane Center Miami FL       AL132019
500 PM AST Fri Sep 27 2019

The satellite appearance of Lorenzo has degraded further since the
last advisory, with only a hint of an eye still apparent in visible
imagery and the cold cloud tops in the eyewall becoming very
asymmetric in infrared imagery.  A recent SSMI/S overpass shows
that the southern portion of the eyewall has eroded, possibly due to
shear or dry air intrusion.  The microwave imagery also suggests an
outer convective band is forming, but it is not yet well enough
defined to call it an outer eyewall.  Satellite intensity estimates
have continued to decrease, and the initial intensity is lowered to
110 kt as a blend of the various estimates.  The hurricane continues
to have excellent outflow in the northern semicircle.

The initial motion remains 330/12 kt.  There is no change in the
track forecast philosophy or the forecast confidence, as Lorenzo
should turn northward and then northeastward during the next few
days as it moves around the western edge of a mid-level ridge
centered over the eastern Atlantic.  Later in the forecast period,
the cyclone is expected to accelerate northeastward in the
mid-latitude westerlies ahead of a deep-layer trough approaching
from the west.  The track guidance for this advisory, while it
remains tightly clustered in direction, is a little slower than the
previous guidance.  Based on this, the new forecast track is just a
little slower than the previous forecast.

Lorenzo will be passing over sea surface temperatures of 27-28C for
the next 48-72 h.  However, it will be in an environment of moderate
vertical shear due to an upper-level trough not far to the west.
The intensity guidance responds to this by showing gradual
weakening during this time, and the new intensity forecast follows
the trend of the guidance.  There is a possibility of fluctuations
in intensity caused by eyewall replacement cycles superimposed on
this weakening trend.  After 72 h, the hurricane should encounter
stronger mid-latitude westerlies, move over cooler sea surface
temperatures, and eventually merge with the above-mentioned
deep-layer trough.  As this occurs, Lorenzo is forecast to undergo
extratropical transition, with this being complete by 120 h.
Current indications from the global models are that Lorenzo will
retain hurricane strength through the transition.


FORECAST POSITIONS AND MAX WINDS

INIT  27/2100Z 20.3N  43.6W  110 KT 125 MPH
 12H  28/0600Z 21.6N  44.1W  105 KT 120 MPH
 24H  28/1800Z 23.3N  44.3W  100 KT 115 MPH
 36H  29/0600Z 25.0N  44.0W  100 KT 115 MPH
 48H  29/1800Z 26.6N  43.3W  100 KT 115 MPH
 72H  30/1800Z 30.3N  41.1W   95 KT 110 MPH
 96H  01/1800Z 35.5N  36.0W   90 KT 105 MPH
120H  02/1800Z 44.0N  26.5W   80 KT  90 MPH...POST-TROP/EXTRATROP

$$
Forecaster Beven

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