ZCZC MIATCDAT4 ALL
TTAA00 KNHC DDHHMM
 
Tropical Storm Eta Discussion Number  38
NWS National Hurricane Center Miami FL       AL292020
400 PM EST Mon Nov 09 2020
 
Eta's convective pattern now consists of mainly a compact ring of 
inner-core convection with cloud tops of -60C to -70C. The earlier 
main outer convective band located in the northeast quadrant has 
weakened considerably, and the inflow into that feature is now being 
shunted westward into Eta's inner-core region. Visible and water 
vapor satellite images also indicate that weak anticyclonic cirrus 
outflow has recently developed over the inner core. The last recon 
pass through Eta a few hours ago showed a pressure rise to 997 mb 
that was followed by a pressure decrease to 995 mb on the last pass. 
Both flight-level and SFMR-derived surface winds had also decreased 
and only supported around 45 kt, which is the initial intensity used 
for this advisory.
 
The initial motion estimate is southwestward, or 235/14 kt. Mid- and 
upper-level water vapor images show a cut-off low located over the 
extreme northwestern Caribbean Sea near the Isle of Youth. This 
feature, in conjunction with a deep-layer ridge extending across 
Florida and the Gulf of Mexico, is expected to produce northeasterly 
flow that will keep Eta moving southwestward for the next 24-36 
hours. However, the cyclone will gradually slow down during that 
time as a broad deep-layer trough moving across the central and 
south-central U.S. weakens the ridge over the Gulf, causing Eta to 
stall or make a small loop around 36 hours. By 48-60 hours and 
beyond, the aforementioned trough is forecast to lift out to the 
northeast, allowing at least some of the Gulf ridge to build back 
in, slowing down Eta's poleward progress or even possibly trapping 
the cyclone over the northeastern Gulf of Mexico. The global and 
regional models are in very good agreement on the developing track 
scenario through about 72 hours, and then diverge significantly 
thereafter, with the bulk of the guidance taking a much weaker Eta 
northwestward or northward into strong shear conditions. However, 
the Navy COAMPS-TC model strengthens Eta to near major hurricane 
status and takes the cyclone northeastward, while the HMON model 
also intensifies the cyclone into a major hurricane, but leaves it 
trapped over the southeastern Gulf of Mexico. The latter two 
scenarios are considered to be outliers due to the abundance of very 
dry air surrounding Eta and an expected increase in the deep-layer 
shear to more than 25 kt by 96 and 120 hours. The new official 
forecast track is to the left or west of the previous advisory 
track, but not as far west as the consensus models, which take a 
significantly weaker and more shallow cyclone toward the 
north-central Gulf coast.
 
Some re-strengthening appears more likely now that Eta has shed a 
lot of outer convective baggage and has become more compact, and 
has developed a donut ring of inner-core convection and some modest 
upper-level outflow in all quadrants. Eta's best opportunity for 
intensification should come during the next 36 hours when the 
cyclone will be moving over the warm waters of the Gulf of Mexico 
Loop Current and the deep-layer vertical wind shear gradually 
decreases to less than 10 kt. Although occasional intrusions of very 
dry air will prevent rapid intensification from occurring, some 
gradual strengthening seems to be in order given the other favorable 
environmental conditions and the cyclone's new smaller size. By 48 
hours and beyond, increasing vertical wind shear and dry air 
entrainment should cause steady weakening of the cyclone through end 
of the forecast period. However, if Eta takes a more northwestward 
track like some of the NHC model guidance is indicating, then the 
cyclone will get sheared more and weaken sooner than indicated in 
the official forecast.  The new NHC intensity forecast is similar to 
the previous advisory, and but is lower than intensity consensus 
models IVCN and HCCA, which re-strengthen Eta to a 65-70 kt 
hurricane.
 
Key Messages:
 
1. Heavy rainfall from Eta will continue across portions of Cuba, 
the Bahamas, and southern Florida and spread north into central 
Florida. Additional flash flooding is possible across inundated 
urban areas of southeast Florida today. Flash and urban flooding 
will also be possible for Cuba, the Bahamas and the remainder of 
southern Florida over the next several days.
 
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.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  09/2100Z 23.7N  84.8W   45 KT  50 MPH
 12H  10/0600Z 23.2N  85.3W   50 KT  60 MPH
 24H  10/1800Z 23.4N  85.5W   55 KT  65 MPH
 36H  11/0600Z 24.3N  85.5W   60 KT  70 MPH
 48H  11/1800Z 25.6N  85.4W   55 KT  65 MPH
 60H  12/0600Z 26.5N  85.6W   50 KT  60 MPH
 72H  12/1800Z 27.2N  85.4W   45 KT  50 MPH
 96H  13/1800Z 28.0N  85.4W   40 KT  45 MPH
120H  14/1800Z 28.6N  85.6W   30 KT  35 MPH
 
$$
Forecaster Stewart
 
NNNN