[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 051450
TCDAT4

Tropical Depression Eta Discussion Number  20
NWS National Hurricane Center Miami FL       AL292020
900 AM CST Thu Nov 05 2020

Eta remains disorganized this morning, as visible imagery suggests
that the circulation has become elongated and that multiple
vorticity centers may be present inside the larger cyclonic
envelope.  The center position for this advisory, which is over
northwestern Honduras, is closer to convection in the northwestern
semicircle than was the case 6 h ago, so the cyclone is being
maintained as a tropical depression at this time.

The initial motion is a somewhat uncertain 305/8 kt.  Eta or its
remnants should move generally northwestward today, then turn
northward tonight. From 24-72 h, the system should move
northeastward in response to a developing mid- to upper-level
trough over the central and eastern Gulf of Mexico.  From 72-120 h,
the trough is forecast to become a closed mid- to upper-level low
in the vicinity of western Cuba, with the center of Eta likely to
turn west-northwestward on the north side of the low.  While the
global models are in good agreement with this synoptic evolution,
there is a significant spread in the forecast tracks between the
fastest and farthest east GFS and the slowest and farthest west
UKMET.  The new forecast track lies between these extremes in best
overall agreement with the ECMWF and Canadian models, and it calls
for the system to be near western Cuba and the Cayman Islands in
60-72 h, and then be over the southeastern Gulf of Mexico by the
end of the forecast period.

Little change in strength is expected before the center moves back
over the Caribbean, but there is still a chance that Eta could
degenerate to a remnant low pressure area later today if the
convection does not persist.  Intensification is expected over the
warm waters of the Caribbean Sea from 24-72 h, although this may be
slowed by southwesterly shear caused by the aforementioned trough.
As the trough cuts off near or over Eta between 72-120 h, the
global models suggest that the system could strengthen while
acquiring at least some subtropical or hybrid characteristics due
to upper-level cold air entrainment.  The new intensity forecast is
little changed from the previous forecast, and in the latter part of
the forecast period it lies near the intensity consensus.  It should
be noted that while Eta regaining hurricane strength cannot be ruled
out, there is little support for that in the current guidance.

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 late this week. 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  05/1500Z 15.1N  87.8W   25 KT  30 MPH...INLAND
 12H  06/0000Z 15.7N  88.0W   25 KT  30 MPH...INLAND
 24H  06/1200Z 16.8N  87.6W   25 KT  30 MPH...OVER WATER
 36H  07/0000Z 17.8N  86.2W   30 KT  35 MPH
 48H  07/1200Z 19.0N  84.5W   35 KT  40 MPH
 60H  08/0000Z 20.1N  83.0W   45 KT  50 MPH
 72H  08/1200Z 21.3N  81.2W   50 KT  60 MPH
 96H  09/1200Z 23.0N  80.0W   50 KT  60 MPH
120H  10/1200Z 24.0N  83.0W   55 KT  65 MPH

$$
Forecaster Beven
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