[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 020249
TCDAT3

Hurricane Lorenzo Discussion Number  39
NWS National Hurricane Center Miami FL       AL132019
1100 PM AST Tue Oct 01 2019

Lorenzo's convective cloud pattern has eroded significantly during
the past 6 hours, with an eye no longer evident in infrared
satellite imagery.  However, a ragged remnant eye feature is still
present in passive microwave imagery, and that data indicates that
the mid- and upper-level circulations are tilted about 15-20 nmi
northeast of the low-level center due to strong southwesterly
vertical wind shear of 25-30 kt. Satellite intensity estimates have
also decreased and now support around 75 kt. However, the intensity
is being maintained at 85 kt due to Lorenzo's faster forward speed,
which is now about 10 kt more than it was on the previous advisory,
offsetting the possible decrease in the tangential winds.  The 64-,
50-, and 34-kt wind radii had to once again be expanded in nearly
every quadrant, but especially to the southeast, based on a 2305 UTC
ASCAT-B overpass. The larger wind field is now expected to result in
sustained hurricane-force winds occurring across portions of the
western and central Azores on Wednesday morning.

Despite the hurricane's extremely large size, Lorenzo has continued
to accelerate northeastward and is now moving 045/35 kt. Lorenzo's
forward speed should gradually level off near 40 kt on Wednesday,
and then gradually begin to decrease by Thursday morning when the
cyclone turns more eastward toward Ireland.  By late Thursday,
post-tropical Lorenzo is forecast to turn east-southeastward,
crossing Ireland and southern England. The latest NHC model guidance
is tightly packed about the previous forecast track, so only minor
tweaks were required, and new advisory lies close to an average of
the various consensus model forecast tracks.

Lorenzo is currently moving over sea-surface temperatures (SST) near
24 deg C, and that isn't taking into account any cold upwelling that
is likely occurring beneath the very large hurricane.  With only
colder water ahead of the cyclone, coupled with vertical shear
increasing to more than 40 kt by 12 hours, rapid transition to a
powerful post-tropical/extratropical cyclone is expected shortly
after Lorenzo passes the Azores.  However, only gradual weakening is
foreast during the next 24 hours due to baroclinic interaction with
an upper-level trough and frontal system.  After that time, a more
rapid rate of weakening is expected when Lorenzo will be moving over
Ireland and England.

Lorenzo's expansive circulation is producing very large seas over
the north Atlantic. Full information can be found in High Seas
Forecasts from the following agencies:

The NOAA Ocean Prediction Center under AWIPS header NFDHSFAT1, WMO
header FZNT01 KWBC, and online at
ocean.weather.gov/shtml/NFDHSFAT1.php

The UK Met Office under WMO header FQNT21 EGRR and online at
http://www.metoffice.gov.uk/public/weather/marine-high-seas/

Meteo France under WMO header FQNT50 LFPW and online at
http://www.meteofrance.com/previsions-meteo-marine/bulletin/
grandlarge/metarea2

Key Messages:

1.  Lorenzo is expected to bring hurricane- and tropical-storm-force
winds to the Azores beginning within the next couple of hours, with
those dangerous conditions continuing into Wednesday afternoon.
Hurricane and Tropical Storm Warnings are in effect for the Azores.

2.  Swells generated by Lorenzo have spread across much of the
North Atlantic, and are affecting the east coast of the United
States, Atlantic Canada, the Bahamas, portions of the Greater and
Lesser Antilles, and portions of the coast of Europe.  These swells
will produce life-threatening surf and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT  02/0300Z 39.1N  32.7W   85 KT 100 MPH
 12H  02/1200Z 42.7N  28.0W   75 KT  85 MPH...POST-TROP/EXTRATROP
 24H  03/0000Z 48.4N  21.4W   70 KT  80 MPH...POST-TROP/EXTRATROP
 36H  03/1200Z 52.8N  15.8W   65 KT  75 MPH...POST-TROP/EXTRATROP
 48H  04/0000Z 54.1N  10.7W   55 KT  65 MPH...POST-TROP/EXTRATROP
 72H  05/0000Z 52.3N    .5W   35 KT  40 MPH...POST-TROP/EXTRATROP
 96H  06/0000Z...DISSIPATED

$$
Forecaster Stewart
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