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Tropical Storm Eta Discussion Number  42
NWS National Hurricane Center Miami FL       AL292020
300 PM CST Tue Nov 10 2020
 
Eta's convective structure has changed little since the previous 
advisory. A CDO-like feature with cloud tops colder than -70C has 
persisted, with some overshooting tops of -80C to -85C located east 
and southeast of the center. Recent passive microwave satellite 
data indicates that Eta is still sheared from the northwest, with 
an intermittent mid-level eye feature showing up. Satellite 
classifications have essentially remained unchanged, with SAB 
reporting 45-55 kt and TAFB reporting 55 kt. The initial intensity 
remains at 50 kt based on a blend of these satellite 
classifications and a UW-CIMSS SATCON estimates of 45-48 kt.
 
The initial motion estimate is now northward, or 360/06 kt. The 
biggest surprise is the large eastward shift in all of the NHC model 
guidance, which was possibly due at least in part to all of the 
dropsondes that the NOAA G-IV jet aircraft dropped around Eta 
earlier this morning, All of the guidance is now in good agreement 
on a broad, deep-layer trough moving eastward across the 
south-central and southeastern United States, which will erode the 
subtropical ridge to the north of Eta that has been impeding 
Eta's poleward progress he past couple of days. This generally 
northward to northeastward steering pattern is expected to persist 
through the entire 120-h forecast period, with only slight shifts 
east or west of he current forecast track due to how vertically deep 
Eta remains when it reaches the northeastern Gulf of Mexico and 
Apalachee Bay in a few days. The current forecast track maintains 
Eta as at least a moderate tropical cyclone through the period, with 
only a slight bend back toward the northwest when the system is 
expected to interact with an approaching frontal system. The new NHC 
track forecast has been shifted about 150 n mi east of the previous 
advisory track at 96 and 120 hours, and further eastward shifts in 
the track may be required, closer to the consensus models TCVA/TVCN 
and NOAA-HCCA.
 
Eta is forecast to remain in a low-to-moderate vertical wind shear 
environment and over SSTs of at least 27 deg C for the next 36 hours 
or so. Intermittent entrainment of dry mid-level air should prevent 
any rapid strengthening from occurring, but Eta could still become a 
hurricane between in 24 to 36 h before more significant shear begins 
to affect the cyclone. By day 3 and beyond, increasing northwesterly 
vertical wind shear combined with cooler SSTs should cause Eta to 
weaken. The new intensity forecast is essentially the same as the 
previous advisory, and is a little below the consensus models IVCN, 
HCCA, and FSSE, all of which make Eta a hurricane again by 36 hours.

Due to the expected northwesterly shear after 36 hours, the 34-kt 
wind radii were expanded in the eastern semicircle, which is the 
side of the cyclone where most of the deep convection and associated 
stronger winds will be located. Given this and the eastward 
adjustment to the track forecast, a Tropical Storm Watch has been 
issued for portions of the Florida west coast, and a Tropical Storm 
Warning is in effect for the Dry Tortugas.
 
Key Messages:
 
1. Tropical-storm-force winds are possible along portions of the 
Florida Gulf Coast by Thursday afternoon, and a Tropical Storm Watch 
has been issued. Interests elsewhere along the Florida Gulf Coast 
should monitor the progress of Eta, as additional watches may be 
needed tonight.

2. Heavy rainfall from Eta will continue across western Cuba and 
South Florida today and tonight, then potentially spread up the west 
coast of the Florida Peninsula Wednesday through Thursday. 
Additional flash and urban flooding will be possible in South 
Florida, especially across previously inundated areas, and 
eventually along portions of West Florida and the Sun Coast. Flash 
and urban flooding will also be possible for western Cuba.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  10/2100Z 23.2N  85.1W   50 KT  60 MPH
 12H  11/0600Z 24.1N  84.9W   55 KT  65 MPH
 24H  11/1800Z 25.6N  84.8W   60 KT  70 MPH
 36H  12/0600Z 26.9N  84.5W   60 KT  70 MPH
 48H  12/1800Z 27.9N  84.2W   55 KT  65 MPH
 60H  13/0600Z 28.7N  84.0W   45 KT  50 MPH
 72H  13/1800Z 29.1N  84.0W   40 KT  45 MPH
 96H  14/1800Z 29.7N  84.6W   35 KT  40 MPH
120H  15/1800Z 30.7N  84.9W   30 KT  35 MPH...INLAND
 
$$
Forecaster Stewart
 
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