Hurricane Lorenzo Forecast Discussion Number 25

By | September 28, 2019

Issued at 500 PM AST Sat Sep 28 2019


000
WTNT43 KNHC 282040
TCDAT3

Hurricane Lorenzo Discussion Number  25
NWS National Hurricane Center Miami FL       AL132019
500 PM AST Sat Sep 28 2019

A NOAA Hurricane Hunter aircraft conducting a research mission has
been invaluable in helping us to observe reintensification after
Lorenzo's eyewall replacement.  The plane measured a peak 700-mb
flight-level wind of 126 kt and SFMR surface winds as high as 112
kt.  In addition, the latest UW-CIMSS SATCON estimate is 114 kt.
These data support increasing the initial intensity to 115 kt, which
makes Lorenzo a category 4 hurricane again.  The plane also reported
a circular eye 34 n mi wide and a central pressure around 950 mb.

Lorenzo is moving northward, or 355/9 kt, through a gap in the
subtropical ridge.  The western Atlantic ridge is becoming stronger
than the eastern Atlantic ridge, and this should help to nudge
Lorenzo north-northeastward between 24-48 hours.  After that
period, a deep-layer trough over the north Atlantic should turn
Lorenzo northeastward, with the hurricane's forward motion
accelerating as it becomes embedded in the mid-latitude westerlies.
The updated NHC track forecast has been placed near the HCCA model
and the other consensus aids, which keeps it very close to the
previous official forecast, at least through day 4.  Some southward
adjustment of the track was made at day 5 based on the latest
global model guidance.

Fluctuations in Lorenzo's intensity are possible over the next day
or so.  However, on the whole, moderate westerly shear and
decreasing oceanic heat content ahead of the hurricane are expected
to contribute to a very gradual weakening trend over the next 3
days.  After day 3, Lorenzo is forecast to begin interacting with
an approaching cold front from the northwest, which would start
extratropical transition.  The global models indicate that the
transition should be complete soon after 96 hours, so for the
moment the advisory continues to show tropical status on day 4.
Faster weakening is expected during and after extratropical
transition, and the updated NHC intensity forecast has been lowered
slightly from the previous forecast on days 4 and 5.

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.


FORECAST POSITIONS AND MAX WINDS

INIT  28/2100Z 23.3N  45.0W  115 KT 130 MPH
 12H  29/0600Z 24.6N  44.8W  110 KT 125 MPH
 24H  29/1800Z 26.3N  44.3W  105 KT 120 MPH
 36H  30/0600Z 28.0N  43.7W  100 KT 115 MPH
 48H  30/1800Z 29.7N  42.9W   95 KT 110 MPH
 72H  01/1800Z 34.8N  38.0W   90 KT 105 MPH
 96H  02/1800Z 42.5N  26.5W   75 KT  85 MPH
120H  03/1800Z 49.0N  13.0W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Berg

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