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
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.
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.
Hurricane Lorenzo Discussion Number 18
NWS National Hurricane Center Miami FL AL132019
1100 PM AST Thu Sep 26 2019
Lorenzo has intensified even more this evening, with a clear eye
characterized by warm temperatures of up to 17 degrees
Celsius. The eye is now completely surrounded by a ring of
convection with cold cloud tops less than minus 70 degrees Celsius.
The subjective Dvorak intensity estimates from both TAFB and SAB,
as well as the objective intensity estimate from UW-CIMSS ADT
unanimously support increasing the initial intensity to 125 kt.
Lorenzo is a very large hurricane, with tropical storm force winds
extending over 200 n mi from the center in the northern semicircle,
and a cirrus cloud canopy that spans greater than a 10 degree
latitude by 10 degree longitude area.
The initial motion is now north-northwest, or 330/12 kt. Model
guidance is in very good agreement throughout the 5 day period on
the future track of Lorenzo. The hurricane will move through a break
in the subtropical ridge currently to its northwest over the next
couple of days, gradually turning to the north then northeast as it
rounds the periphery of a ridge to its east. Late in the forecast
period, Lorenzo will begin to accelerate as it gets caught in
southwesterly flow ahead of an approaching mid-latitude trough. The
model guidance made a slight shift to the left since the previous
advisory, but since the same guidance shifted right earlier today, I
did not want to make much of a change to the track. The official
forecast track is very near the previous one, and is now on the
right side of the consensus guidance.
The environment around Lorenzo is expected to change little over
the next day or so. Both dynamical and statistical guidance are
suggesting that the hurricane is nearing peak intensity. Therefore
only fluctuations in strength due to eyewall replacement cycles are
expected through about Friday night. Over the weekend, some moderate
westerly shear ahead of the approaching mid-latitude trough could
begin to slowly weaken the cyclone. Late in the forecast period,
the combination of strong upper level southwesterly winds and
cooler sea surface temperatures should cause a faster weakening
trend. The official forecast is essentially an update of the
previous one, and a little higher than most of the guidance through
the first 48 hours.
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