Hurricane Lorenzo Forecast Discussion Number 29

By | September 29, 2019

Issued at 1100 AM AST Sun Sep 29 2019


000
WTNT43 KNHC 291456
TCDAT3

Hurricane Lorenzo Discussion Number  29
NWS National Hurricane Center Miami FL       AL132019
1100 AM AST Sun Sep 29 2019

Satellite and microwave imagery are indicating that Lorenzo is now
weakening. A recent microwave pass showed a broken eyewall as well
as dry air in the southwestern quadrant. Over the past hour, the eye
has begun to fill in. However, outflow remains excellent and cloud
tops remain very cold near the center of the hurricane. A blend of
the latest CI values from TAFB and SAB as well as a recent
subjective intensity estimate from UW-CIMSS suggest the initial
intensity is now 125 kt.

Lorenzo is moving north-northeastward at 9 kt through a weakness in
the subtropical ridge. A mid-latitude trough will approach Lorenzo
from the west in a couple of days. Increasing southwesterly flow
ahead of the trough will force the hurricane to turn northeastward
and accelerate beginning on Monday. The forecast track confidence is
very high through 72 hours, and the new forecast is in good
agreement with the tightly clustered consensus guidance and the
previous forecast. Beyond 72 hours, the guidance now diverges
significantly, likely due to how they are handling the interaction
between Lorenzo and a larger extratropical cyclone near Greenland
late in the forecast period. The majority of the guidance has
shifted to the west by several hundred miles over the past couple of
runs.  However, there remains significant spread between the
operational UKMET/ECMWF which take what's left of Lorenzo toward the
British Isles, and the solutions that absorb the cyclone into the
larger system well over 1000 miles to the west. Based on the recent
shift in the models and the large spread, the official forecast was
only adjusted a little to the left and lies well to the right of the
consensus aids. Needless to say, the forecast track confidence
beyond 72 hours is low at the moment, and may need further
adjustments in the next couple of advisories.

Lorenzo reached its peak intensity last night, and the intensity
guidance is in good agreement that the hurricane will steadily
weaken over the next several days due to increasing southwesterly
shear, dry air entrainment, and progressively cooler SSTs. The NOAA
Hurricane Hunters are still scheduled to investigate Lorenzo later
today, and the data they collect should provide a better assessment
of the hurricane's intensity and structure.  In a few days, Lorenzo
will interact with a frontal zone and begin transitioning to an
extratropical cyclone. This transition is expected to be complete by
96 hours. It is important to note that although Lorenzo is
forecast to weaken through the forecast period, the wind field is
expected to expand at the same time, with tropical-storm-force and
50 kt winds forecast to extend over 300 n mi/ 160 n mi respectively
from the center in 72 hours. The latest intensity forecast is
similar to the previous one, and it is near the HFIP corrected
consensus HCCA.

Earlier input from the Tropical Analysis and Forecast Branch here at
NHC indicates that the large wind field of Lorenzo and its expected
faster forward motion in a few days will likely lead to extreme
enhancement of the wave field and wave growth over the southeastern
portion of the circulation.

Key Messages:

1.  Lorenzo is a large and powerful 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
those islands Tuesday night and Wednesday, and residents there
should monitor the progress of the hurricane. Watches could be
issued for those islands later today or tonight.

2.  Large swells generated by Lorenzo will continue to spread across
much of the north Atlantic basin during the next few days.  These
swells will produce life-threatening surf and rip currents.


FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 25.9N  44.4W  125 KT 145 MPH
 12H  30/0000Z 27.2N  43.9W  115 KT 130 MPH
 24H  30/1200Z 28.9N  43.0W  105 KT 120 MPH
 36H  01/0000Z 31.0N  41.6W  100 KT 115 MPH
 48H  01/1200Z 33.7N  38.9W   95 KT 110 MPH
 72H  02/1200Z 42.0N  29.0W   80 KT  90 MPH
 96H  03/1200Z 50.0N  18.4W   65 KT  75 MPH...POST-TROP/EXTRATROP
120H  04/1200Z 54.9N  11.6W   50 KT  60 MPH...POST-TROP/EXTRATROP

$$
Forecaster Latto

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