[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 072054
TCDAT4

Tropical Storm Eta Discussion Number  30
NWS National Hurricane Center Miami FL       AL292020
400 PM EST Sat Nov 07 2020

An earlier Air Force Reserve Hurricane Hunter aircraft found that
Eta had strengthened to 50 kt with a central pressure of 994 mb.
Since that time, the storm organization is unchanged in satellite
imagery, while the central convection looks a little more ragged in
radar data from Grand Cayman Island and Cuba.  Eta is currently
being affected by 25-35 kt of southwesterly vertical wind shear,
and water vapor imagery shows upper-level dry air approaching the
inner core from the west.

The initial motion now 050/14. There is little change to the
forecast philosophy through the first 96 h of the forecast.  A mid-
to upper-level trough over the Gulf of Mexico should steer Eta
northeastward for the next 12 h or so, which would bring the
center near or over the coast of central Cuba.  Then from 12-96 h,
the trough should cut off into a closed low near western Cuba, with
Eta turning northward and eventually westward near the Florida Keys
and south Florida as it merges with the low.  The track guidance
has shifted a little to the west over Cuba and a little to the
south near Florida, possibly in response to data from the G-IV jet
mission earlier today, and the new track forecast does likewise.
The track guidance becomes quite divergent after 96 h, and the
96-120 h motion is now slower than the previous forecast as a
result.

The intensity forecast is tricky.  Strong upper-level divergence
caused by the trough is allowing the cyclone to strengthen. However,
at some time in the next 24-48 h the shear and dry air entrainment
should prevent any further strengthening.  The intensity guidance
shows a little intensification during the next 24-36 h with the bulk
of the guidance peaking near 60 kt.  After that time, the dry air
should cause at least some weakening.  The new intensity forecast is
increased a bit from the previous forecast to show a 60-kt
intensity at 24 and 36 h.  This requires issuing a hurricane watch
for the Florida Keys and portions of south Florida.

Key Messages:

1. Heavy rainfall will continue across the Cayman Islands, portions
of Cuba, and Jamaica, and will spread north into the Bahamas and
southern Florida. This rain may result in significant,
life-threatening flash flooding and river flooding in Cuba. Flash
and urban flooding will also be possible for the Cayman Islands,
Jamaica, the Bahamas and southern Florida, along with potential
minor river flooding in central Florida.

2. Tropical storm conditions will continue for a few more hours in
portions of the Cayman Islands, and are expected tonight and Sunday
in portions of Cuba and the northwestern Bahamas, where Tropical
Storm Warnings are in effect.

3. Damaging tropical-storm-force winds are expected Sunday night,
with hurricane-force winds possible, in the Florida Keys and
portions of the southern Florida peninsula, where a Tropical Storm
Warning and Hurricane Watch are in effect.  Elsewhere across
portions of the east and west coasts of the Florida peninsula, the
risk of tropical-storm-force winds will extend well away from Eta's
center, and Tropical Storm Watches and Warnings are in effect.

4. A life-threatening storm surge is possible along portions of the
southern coast of the Florida peninsula and the Florida Keys, where
a Storm Surge Watch is in effect. Residents in the Storm Surge Watch
area should follow any advice given by local officials.

FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 20.4N  80.7W   50 KT  60 MPH
 12H  08/0600Z 21.6N  79.4W   55 KT  65 MPH...INLAND
 24H  08/1800Z 23.3N  79.0W   60 KT  70 MPH...OVER WATER
 36H  09/0600Z 24.7N  79.9W   60 KT  70 MPH
 48H  09/1800Z 25.2N  81.2W   55 KT  65 MPH
 60H  10/0600Z 25.7N  82.8W   55 KT  65 MPH
 72H  10/1800Z 26.1N  83.6W   50 KT  60 MPH
 96H  11/1800Z 26.5N  84.0W   50 KT  60 MPH
120H  12/1800Z 27.0N  84.0W   45 KT  50 MPH

$$
Forecaster Beven
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