[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 280856
TCDAT3

Hurricane Lorenzo Discussion Number  23
NWS National Hurricane Center Miami FL       AL132019
500 AM AST Sat Sep 28 2019

Lorenzo's tilt has grown this morning. AMSR2 imagery at 0505 UTC
showed a 20 n mi displacement between the low- and mid-level centers
of the hurricane, a consequence of persistent westerly wind shear.
Satellite-based intensity estimates vary greatly, from 77 to 110 kt,
so the intensity is set to 100 kt as a compromise of all available
data. Despite the decrease in Lorenzo's maximum winds during the
past 24 hours, earlier ASCAT-C data showed that its hurricane-force
wind field has expanded, and now reaches up to 45 n mi to the
northeast of the center.

The lower initial intensity resulted in a slightly lower intensity
forecast through most of the period. The wind shear affecting the
cyclone is forecast to continue, and a slow decrease in Lorenzo's
peak winds is still expected during the next several days. The
official intensity forecast is very near the intensity consensus.
Despite the expected decrease in intensity, the hurricane is not
forecast to decrease in size, and in fact Lorenzo's hurricane-force
wind field could increase further by next week. Because of that,
users are urged to not focus on the exact intensity of Lorenzo since
the cyclone will likely remain a powerful storm well into next week.
By 120 h, all of the global models indicate that Lorenzo will become
post-tropical, and so does the NHC forecast.

The aforementioned microwave data was very helpful in identifying
Lorenzo's center location. The hurricane has continued to move left
of the forecast track, and the initial motion estimate is 330/9 kt.
Despite Lorenzo's recent tendency to move farther west than
anticipated, the hurricane is still forecast to turn northward soon.
After continuing northward and north-northeastward for a day or two,
Lorenzo should accelerate toward the northeast ahead of a deep
mid-latitude trough approaching from the west by mid-week. The NHC
track forecast has been shifted slightly left for the first 48 h to
account for Lorenzo's recent motion, but it is very similar to the
previous forecast at 72 h and beyond. The models are in excellent
agreement for the first 3 days of the forecast but the uncertainty
grows by the end of the period, primarily due to differences in the
forecast forward speed of the cyclone as it recurves and becomes
post-tropical.

FORECAST POSITIONS AND MAX WINDS

INIT  28/0900Z 21.4N  44.8W  100 KT 115 MPH
 12H  28/1800Z 22.7N  44.8W   95 KT 110 MPH
 24H  29/0600Z 24.5N  44.7W   90 KT 105 MPH
 36H  29/1800Z 26.0N  44.2W   90 KT 105 MPH
 48H  30/0600Z 27.6N  43.5W   85 KT 100 MPH
 72H  01/0600Z 31.5N  40.9W   85 KT 100 MPH
 96H  02/0600Z 38.0N  32.5W   80 KT  90 MPH
120H  03/0600Z 48.0N  19.0W   70 KT  80 MPH...POST-TROP/EXTRATROP

$$
Forecaster Zelinsky
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