Hurricane Lorenzo Forecast Discussion

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000
WTNT43 KNHC 300242
TCDAT3

Hurricane Lorenzo Discussion Number  31
NWS National Hurricane Center Miami FL       AL132019
1100 PM AST Sun Sep 29 2019

There haven't been a lot of changes with Lorenzo this evening, with
a small cloud-filled eye remaining visible and an enormous cloud
shield expanding in the northern semicircle.  Satellite intensity
estimates support a somewhat lower intensity than the previous
advisory, so the initial wind speed is set to 95 kt.  It should be
emphasized that even though the peak winds are down since yesterday,
the area of the hurricane-force winds has more than doubled during
that time.

Earlier aircraft data indicated that the large hurricane is
upwelling a significant amount of cooler waters under the storm, and
this is anticipated to cause Lorenzo to slowly weaken during the
next couple of days.  While the SSTs drop off considerably after
late tomorrow, which would normally cause faster weakening, most of
the guidance is showing a favorable trough interaction at that time
with strong upper-level divergence.  These effects are expected to
offset, and Lorenzo is likely to be a category 1 or 2 hurricane near
the Azores.  Little change was made to the previous forecast, except
to raise the intensity a little higher near the Azores after more
heavily weighting the global models, which have been good performers
for this cyclone.  The guidance is in very good agreement on Lorenzo
becoming an extratropical cyclone in about 72 hours, and that is
reflected in the latest forecast.

Lorenzo continues north-northeastward at 9 kt through a break in the
subtropical ridge.  The forecast track confidence remains very high
through 48 hours as the hurricane is accelerated toward the
northeast ahead of a mid-latitude trough, and the new forecast is
essentially an update of the previous one.  After that time,
however, there is a very large spread in the guidance caused by
whether Lorenzo is captured by the mid-latitude trough or if it
remains separate.  There isn't much change in the newest guidance,
although it should be noted that the 12Z ECMWF solution is pretty
far east of its ensemble mean.  The forecast track confidence is
extremely low beyond 72 hours, and the new NHC track was nudged
just a little to the left from the previous advisory, slightly east
of the various consensus aids.


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.  Hurricane and Tropical Storm Watches
have been issued for the Azores, and these winds could start late
Tuesday or early Wednesday.

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  30/0300Z 27.6N  43.5W   95 KT 110 MPH
 12H  30/1200Z 28.9N  42.9W   90 KT 105 MPH
 24H  01/0000Z 31.0N  41.5W   90 KT 105 MPH
 36H  01/1200Z 33.9N  38.6W   85 KT 100 MPH
 48H  02/0000Z 37.5N  34.2W   85 KT 100 MPH
 72H  03/0000Z 48.0N  22.5W   70 KT  80 MPH...POST-TROP/EXTRATROP
 96H  04/0000Z 53.0N  17.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  05/0000Z 54.0N  17.0W   45 KT  50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Blake



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