[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 031448
TCDAT4

Hurricane Eta Discussion Number  12
NWS National Hurricane Center Miami FL       AL292020
1000 AM EST Tue Nov 03 2020

Eta appears to have peaked in intensity overnight as an eyewall
replacement cycle occurred early this morning. Radar data from San
Andres revealed concentric eyewalls and the last images received
from that radar early this morning suggests that the inner-eye wall
had weakened.  Around that time, the eye became cloud filled and
less distinct in infrared satellite imagery.  An Air Force Reserve
reconnaissance aircraft that provided a couple of
center fixes this morning reported that the minimum pressure has
risen about 15 mb since last evening.  The plane measured a peak
flight-level wind of 127 kt, and a few SFMR winds slightly higher,
but those winds were flagged as suspect.  A dropwindsonde in the
southeastern eyewall measured a surface wind of 138 kt, but the
mean-layer average winds from the sonde supports a much lower
intensity, and the instantaneous surface wind from that instrument
is likely more representative of a wind gust.  Based on the above
data, the initial intensity is set at 125 kt for this advisory.
Nonetheless, Eta is an extremely severe hurricane, capable of
causing very high storm surges and catastrophic damage. Once the
center of the hurricane moves onshore later today, rapid weakening
is expected.  It is still not certain if the surface circulation
will survive its trek over Central America during the next several
days, but the official forecast continues to show the remnants of
Eta emerging over the northwestern Caribbean Sea late this week.

Eta has been meandering just offshore of the coast of Nicaragua this
morning, but the longer term motion is 255/4 kt.  The hurricane
should turn westward very soon with the center crossing the coast
today.  A ridge to the north of Eta should steer the cyclone on a
faster westward to west-northwestward heading over northern
Nicaragua and Honduras over the next couple of days. After 72 hours,
a developing trough over the northern Gulf of Mexico should cause
Eta or its remnants to turn northward and then northeastward.  Given
that the system is expected to remain over land for at least a
couple of days, there continues to be significant uncertainty in the
long range portion of the track and intensity forecast.

Since Eta is likely to be a very slow-moving system after it makes
landfall in Central America, torrential rains and inland flooding
will be an extremely serious threat over the next few days.

Key Messages:

1. Catastrophic wind damage is expected where Eta's eyewall moves
onshore along the northeastern coast of Nicaragua. Tropical-storm-
force or greater winds are already occuring within the Hurricane
Warning area in Nicaragua.  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 14 to 21 feet above
normal tide levels in some parts of the hurricane warning area.

3. Through Friday evening, 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, El Salvador, southern Haiti, and the
Cayman Islands.


FORECAST POSITIONS AND MAX WINDS

INIT  03/1500Z 13.6N  83.2W  125 KT 145 MPH
 12H  04/0000Z 13.5N  83.8W  100 KT 115 MPH...INLAND
 24H  04/1200Z 13.7N  84.9W   45 KT  50 MPH...INLAND
 36H  05/0000Z 14.2N  86.5W   30 KT  35 MPH...INLAND
 48H  05/1200Z 14.7N  88.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  06/0000Z 15.2N  89.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  06/1200Z 15.7N  89.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  07/1200Z 17.5N  86.5W   25 KT  30 MPH...OVER WATER
120H  08/1200Z 20.0N  82.5W   35 KT  40 MPH

$$
Forecaster Brown
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