[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 022052
TCDAT4

Hurricane Eta Discussion Number   9
NWS National Hurricane Center Miami FL       AL292020
400 PM EST Mon Nov 02 2020

Eta is an extremely impressive hurricane in both visible and
infrared satellite imagery.  The hurricane has a very small eye that
is located within a symmetric Central Dense Overcast with cloud top
temperatures below -80C.  Although objective Dvorak estimates are
lower due to the technique's difficulty in analyzing the correct
scene type because of the pinhole eye, data T-numbers from both TAFB
and SAB analysts reached 6.0 on the Dvorak scale at 18Z, which
equates to a wind speed of 115 kt.  A recent UW/CIMSS SATCON
intensity estimate also supports category 4 intensity.  As mentioned
in previous advisories over the past 24 hours, the environment ahead
of Eta is forecast to remain quite favorable with low vertical wind
shear and warm sea surface temperatures.  These conditions should
allow for additional strengthening, however a difficult-to-predict
eyewall replacement cycle could begin at any time which could cause
Eta's intensity to begin to level off.  Since there are no signs of
an eyewall replacement yet, the updated NHC intensity forecast calls
for continued rapid strengthening for another 6 to 12 hours, and it
is again at the upper-end of the guidance envelope. After landfall,
Eta should quickly weaken while it moves over the mountainous
terrain of Central America.

The hurricane has turned west-southwestward with an initial motion
estimate of 255/8 kt.  The track forecast reasoning is unchanged
from this morning.  A mid-level ridge over the south-central United
States should steer Eta west-southwestward toward the coast of
Nicaragua with the hurricane making landfall tonight or early
Tuesday.  After landfall, Eta is forecast to turn westward, and then
west-northwestward while it moves over Central America through
midweek.  Eta's surface circulation may not survive its trek over
the mountainous terrain of Central America, but most of the global
models continue to depict a cyclone over the northwestern Caribbean
Sea by later this week and into the weekend which appears to
develop from at least a part of Eta's remnants.  Therefore, the NHC
track forecast continues to show the system emerging over the
northwestern Caribbean late in the period, however the long range
portion of the forecast remains quite uncertain.

Since Eta is likely to be a very slow-moving system after it makes
landfall in Central America, torrential rains and flooding will be
a major threat.

Key Messages:

1. Catastrophic wind damage is expected where Eta's eyewall moves
onshore along the northeastern coast of Nicaragua tonight or early
Tuesday.  Tropical storm force winds are beginning to reach the
coast within the Hurricane Warning area in Nicaragua, and residents
there should have completed their preparations.  A Tropical Storm
Warning is also in effect for the northeastern coast of Honduras.

2. A catastrophic and life-threatening storm surge, along with
destructive waves, are expected along portions of the northeastern
coast of Nicaragua near and to the north of where the center makes
landfall.  Water levels could reach as high as 12 to 18 feet above
normal tide levels in some parts of the hurricane warning area.
Preparations to protect life and property should now be complete.

3. Through Friday evening, heavy rainfall from Eta will likely
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, El Salvador, southern
Haiti, and the Cayman Islands.

FORECAST POSITIONS AND MAX WINDS

INIT  02/2100Z 14.5N  82.3W  115 KT 130 MPH
 12H  03/0600Z 14.1N  83.1W  130 KT 150 MPH
 24H  03/1800Z 14.0N  83.7W   90 KT 105 MPH...INLAND
 36H  04/0600Z 14.0N  84.5W   45 KT  50 MPH...INLAND
 48H  04/1800Z 14.2N  85.5W   30 KT  35 MPH...INLAND
 60H  05/0600Z 14.7N  86.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  05/1800Z 15.5N  88.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  06/1800Z 16.7N  88.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  07/1800Z 18.0N  86.0W   30 KT  35 MPH...TROPICAL DEPRESSION

$$
Forecaster Brown/Berg
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