Tropical Storm ETA (Text)

Tropical Storm Eta Discussion Number  37
NWS National Hurricane Center Miami FL       AL292020
1000 AM EST Mon Nov 09 2020
Eta's overall appearance in satellite radar imagery has become quite 
fragmented, with inner-core convection having become vertically 
shallow and broken due to mid-level dry air entrainment. Some of the 
recent Air Force Reserve reconnaissance flight-level data indicate 
that dry air has worked way down to the 850-mb level based dewpoint 
spreads of more than 8 deg C. In the northeastern quadrant, a large 
curved convective band persists that has produced widespread 
rainfall amounts exceeding 10 inches along with strong gusty winds 
across portions of the southern Florida peninsula. However, even 
that band of thunderstorms has become less pronounced in both 
satellite radar imagery over the past few hours. Doppler velocities 
over land and over water have also come decreased significantly, and 
the latest reconnaissance flight-level (58 kt) and SFMR surface wind 
data (49 kt) supports lowering the intensity to 50 kt. The decrease 
in intensity is also supported by the gradual rise in the central 
pressure, which is now up to 994 mb.

Eta has finally made the expected southwestward turn, and the 
initial motion is now 235/12 kt. A strong deep-layer ridge across 
the Gulf of Mexico, Florida, and near the U.S. east coast is 
expected to keep Eta moving southwestward for the next 24-36 hours, 
accompanied by a steady decrease in forward speed. Steering currents 
are forecast to collapse by 36-48 hours, causing Eta to possibly 
stall and/or make a small loop just northwest of western Cuba. By 60 
hours and beyond, a broad mid-latitude trough currently located over 
the Rocky Mountains is forecast to move eastward and gradually erode 
the portion of the ridge over the Gulf of Mexico, allowing Eta 
slowly move northward to north-northeastward through 20 hours. 
However, there remains considerable divergence between the global 
models on days 4 and 5 with regards to how far north Eta will move, 
with the ECMWF showing a more northward progression while the GFS 
and UKMET models show the trough lifting out and not eroding the 
ridge as much. For now, the official forecast track remains a 
compromise of these two extremes, and shows a slow poleward 
progression on days 3-5, similar to the consensus models TCVA and 
Eta could still re-strengthen some during the 24-48 hour period when 
the cyclone will be moving over the warm waters of the Gulf of 
Mexico Loop Current and the wind shear gradually decrease to less 
than 10 kt. However, occasional intrusions of very dry air will 
likely continue to plague the system, which would prevent any rapid 
intensification from occurring and could keep Eta from regaining 
hurricane status. By 48 hours and beyond, increasing vertical wind 
shear and dry air should cause a gradual weakening of the cyclone 
through end of the forecast period. The new NHC intensity forecast 
is a little lower than the previous advisory, and closely follows 
the intensity consensus models IVCN and HCCA.
Key Messages:
1. Heavy rainfall from Eta will continue across portions of Cuba, 
the Bahamas, and southern and central Florida. Life-threatening 
flash flooding will be possible across urban areas of southeast 
Florida today.  Flash and urban flooding will also be possible for 
Cuba, the Bahamas and the remainder of southern Florida, along with 
potential minor river flooding in central Florida.

2. Eta could approach the Florida Gulf Coast later this week as a 
tropical storm, and possibly bring impacts from rain, wind, and 
storm surge. Interests in this area should monitor the progress of 
Eta and updates to the forecast this week.
INIT  09/1500Z 24.6N  83.4W   50 KT  60 MPH
 12H  10/0000Z 23.9N  84.7W   50 KT  60 MPH
 24H  10/1200Z 23.6N  85.3W   55 KT  65 MPH
 36H  11/0000Z 24.5N  85.4W   60 KT  70 MPH
 48H  11/1200Z 25.6N  85.5W   55 KT  65 MPH
 60H  12/0000Z 26.5N  85.3W   55 KT  65 MPH
 72H  12/1200Z 27.2N  85.1W   50 KT  60 MPH
 96H  13/1200Z 28.4N  84.4W   45 KT  50 MPH
120H  14/1200Z 29.6N  83.7W   35 KT  40 MPH...INLAND
Forecaster Stewart

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Page last modified: Thursday, 31-Dec-2020 12:10:47 UTC