[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 052054
TCDAT4

Tropical Depression Eta Discussion Number  21
NWS National Hurricane Center Miami FL       AL292020
300 PM CST Thu Nov 05 2020

The low-level circulation of Eta has become disorganized to the
point that the system more resembles a remnant low than a tropical
cyclone.  However, the system continues to produce convection in an
area just north and northwest of the estimated center position, as
well as in a cluster well to the northeast.  Based on this, and the
expectation that the system will start re-developing during the next
several hours as it moves back over water, Eta is maintained as a
tropical depression for this advisory.  The initial intensity is
increased to 30 kt based on scatterometer data, with those winds
occuring well to the northeast of the center.

The center appears to be just south of the northwestern coast of
Honduras, and the initial motion is an uncertain 330/7.  During the
next 24 h, Eta should recurve northeastward in southwesterly flow
between a ridge over the central Caribbean and a developing mid- to
upper-level trough over the central Gulf of Mexico.  This motion
should persist through about 72 h.  After that, the trough is
forecast to become a closed low in the vicinity of western Cuba,
with Eta turning to the west-northwest as it interacts or merges
with the low.  While the models are in good agreement with the
synoptic pattern, they are in poor agreement on the details of the
track.  The forecast tracks show possible landfalls in Cuba
anywhere between 77W-83W, and after the turn some of the tracks are
as far north as southern Florida while other stay over Cuba.  In
addition, there is a significant speed difference between the
faster GFS/HWRF/HMON and the slower Canadian/ECMWF/UKMET.  The
low-confidence official forecast compromises between these various
extremes and is not changed much from the previous forecast.

Little change in strength is expected during the next 12 h or so as
Eta starts to re-organized over water.  After that, gradual
strengthening is expected until the system reaches Cuba in about
72 h, with the main limiting factor being increasing southwesterly
shear during that time.  From 72-120 h, there is a possibility that
Eta will take on subtropical or hybrid characteristics as it
interacts with the developing upper-level low.  The intensity
forecast will be held at 50 kt during that time due to this
interaction.  The new intensity forecast has only minor tweaks from
the previous forecast.  However, it lies below the bulk of the
intensity guidance for the first 60 h and above the bulk of the
guidance from 72-120 h.

The new forecast track, intensity, and wind radii require a
Tropical Storm Watch for the Cayman Islands at this time.  A
Tropical Storm Watch will likely be required for portions of Cuba
later tonight or on Friday.

Key Messages:

1. Through Monday morning, heavy rainfall from Eta will lead to
catastrophic, life-threatening flash flooding and river flooding
across portions of Central America, along with landslides in areas
of higher terrain.  Flash and river flooding is also possible across
Jamaica, southeast Mexico, the Cayman Islands and western Cuba.

2. Eta is forecast to regain tropical storm strength over the
northwestern Caribbean Sea in a day or so. Although the details of
the future track and intensity of Eta are uncertain, there is an
increasing risk of impacts from wind and rainfall in portions of the
Cayman Islands, Cuba, southern Florida and the Florida Keys this
weekend and early next week.


FORECAST POSITIONS AND MAX WINDS

INIT  05/2100Z 15.7N  87.7W   30 KT  35 MPH...INLAND
 12H  06/0600Z 16.4N  87.8W   30 KT  35 MPH...OVER WATER
 24H  06/1800Z 18.1N  86.3W   35 KT  40 MPH
 36H  07/0600Z 19.1N  84.8W   40 KT  45 MPH
 48H  07/1800Z 20.1N  83.1W   45 KT  50 MPH
 60H  08/0600Z 21.3N  81.5W   45 KT  50 MPH
 72H  08/1800Z 22.4N  80.1W   50 KT  60 MPH...INLAND
 96H  09/1800Z 23.5N  82.0W   50 KT  60 MPH...OVER WATER
120H  10/1800Z 24.5N  84.5W   55 KT  65 MPH

$$
Forecaster Beven
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