[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 290833
TCDAT3

Hurricane Lorenzo Discussion Number  28
NWS National Hurricane Center Miami FL       AL132019
500 AM AST Sun Sep 29 2019

The satellite appearance of Lorenzo is not quite as impressive as it
was several hours ago.  Although the eye is still very distinct,
the cloud tops are not as cold in the eyewall and there are a few
dry slots evident beyond the inner core.  The initial wind speed is
lowered just slightly to 135 kt, but based on the latest satellite
estimates this is probably generous.  The NOAA Hurricane Hunters are
scheduled to investigate Lorenzo later today, and the data they
collect should provide a better assessment of the hurricane's
intensity and structure.  Very intense hurricanes like Lorenzo are
usually not able to maintain their intensity for very long.  Since
Lorenzo will be moving toward cooler waters and into an environment
of drier air and higher wind shear during the next several days,
steady weakening is forecast.  Lorenzo is now expected to become
extratropical by day 4, when the cyclone will be over SSTs colder
than 20 C.  The NHC intensity forecast is in good agreement with the
consensus models, IVCN, IVDR, and HCCA.

Lorenzo is still moving northward at 9 kt through a break in the
Atlantic subtropical ridge.  A mid- to upper-level trough currently
over eastern Canada is expected to amplify when it reaches the
central Atlantic, which should cause Lorenzo to accelerate to the
northeast during the next few days.  This motion should take the
core of Lorenzo near or just west of the Azores late Tuesday and
Wednesday.  After that time, there are significant differences in
the models on whether or not Lorenzo interacts with an extratropical
low over the north Atlantic.  The ECMWF and UKMET models show little
interaction with that low and show Lorenzo moving east-northeastward
in the westerlies toward northwestern France, Ireland, and the
United Kingdom.  On the other hand, the GFS, HWRF, and HMON models
show Lorenzo rotating around the eastern side of the low and
remaining over the Atlantic.  The spread in the models is incredibly
large, about 1300 n mi by day 5.  Given the high uncertainty at this
time, only small changes were made to the NHC track forecast, and
this one favors the UKMET and ECMWF solutions.  However, confidence
in the long-term track is very low and adjustments may be needed
later today.

The Tropical Analysis and Forecast Branch here at NHC provided
input 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.

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  29/0900Z 25.1N  44.6W  135 KT 155 MPH
 12H  29/1800Z 26.4N  44.2W  125 KT 145 MPH
 24H  30/0600Z 28.0N  43.5W  115 KT 130 MPH
 36H  30/1800Z 29.9N  42.5W  110 KT 125 MPH
 48H  01/0600Z 32.2N  40.5W  105 KT 120 MPH
 72H  02/0600Z 39.4N  32.1W   90 KT 105 MPH
 96H  03/0600Z 47.8N  20.0W   70 KT  80 MPH...POST-TROP/EXTRATROP
120H  04/0600Z 53.5N  10.0W   55 KT  65 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi
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