[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 271442
TCDAT3

Hurricane Lorenzo Discussion Number  20
NWS National Hurricane Center Miami FL       AL132019
1100 AM AST Fri Sep 27 2019

The structure of Lorenzo in conventional satellite imagery has
decayed a little since the last advisory, with the eye becoming
less distinct and the eyewall convection becoming more asymmetric.
There is no current microwave imagery to show whether this
weakening might be due to the start of an eyewall replacement
cycle or not.  The various subjective and objective satellite
intensity estimates have decreased a little, so the initial
intensity is reduced to 120 kt.  The hurricane has excellent cirrus
outflow in all directions except to the southwest.

The initial motion is 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.  By the end of the forecast period, Lorenzo is
expected to accelerate northeastward in the mid-latitude westerlies
ahead of a deep-layer trough approaching from the west.  The new
forecast track is nudged a little to the left of the previous track
based mainly on the initial position, and it lies near the various
consensus models.

Lorenzo is currently passing over a tongue of slightly cooler sea
surface temperatures, and it is forecast to reach slightly warmer
water in 12-24 h.  After that, it stays over sea surface
temperatures near 28C through about 72 h.  During this time, the
intensity will be controlled mainly by internal eyewall replacement
cycles and some ups and downs in the vertical shear as the hurricane
interacts with a couple of upper-level troughs.  The intensity
guidance shows a slow weakening trend during this time, and the NHC
intensity forecast follows this.  However, it would not be
surprising to see some fluctuations in intensity occur.  After 72 h,
the cyclone will become embedded in the mid-latitude westerlies and
move over much colder water.  This, and the approach of the
aforementioned deep-layer trough, will lead to extratropical
transition that will be underway, but likely not complete, by 120 h.


FORECAST POSITIONS AND MAX WINDS

INIT  27/1500Z 19.4N  42.9W  120 KT 140 MPH
 12H  28/0000Z 20.8N  43.6W  115 KT 130 MPH
 24H  28/1200Z 22.6N  44.1W  110 KT 125 MPH
 36H  29/0000Z 24.2N  44.0W  105 KT 120 MPH
 48H  29/1200Z 25.9N  43.4W  105 KT 120 MPH
 72H  30/1200Z 29.6N  41.2W  100 KT 115 MPH
 96H  01/1200Z 34.5N  37.0W   90 KT 105 MPH
120H  02/1200Z 42.5N  28.5W   80 KT  90 MPH

$$
Forecaster Beven
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