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Tropical Storm Norbert Discussion Number   7
NWS National Hurricane Center Miami FL       EP192020
300 AM MDT Wed Oct 07 2020
 
Norbert has weakened as entrainment of dry air has disrupted the 
compact system. The center was partially exposed overnight, but 
recent infrared imagery shows a new burst of deep convection near 
the center. Microwave imagery and ASCAT scatterometer wind data 
indicated the center had drifted southwest from its previous 
position, as the storm is beginning to meander within the weak 
steering flow. The initial intensity has been lowered to 35 kt based 
on the recent ASCAT-A overpass that showed a peak wind of 33 kt, as 
well as a T2.5 Dvorak estimate from TAFB. 
 
The intensity forecast for Norbert remains tricky given its small 
circulation and the presence of dry air in the surrounding 
environment. Sea-surface temperatures are more than sufficient for 
at least modest strengthening, but the question will be whether 
Norbert can survive the increased southeasterly shear that the 
SHIPS guidance calls for during the next 24-48 h. If so, Norbert 
may remain a tropical storm through the next 5 days. Alternatively, 
the shear and additional bouts of dry air entrainment could weaken 
the system to a depression or even a remnant low late in the 
forecast period. While small intensity changes due to diurnal 
fluctuations in convection are certainly possible, the official NHC 
forecast keeps Norbert's intensity forecast at 35 kt in 
consideration of the mixed signals noted in the latest intensity 
guidance.
 
As previously mentioned, the center of Norbert has drifted to the 
southwest overnight. The storm is expected to remain nearly 
stationary over the next couple of days as distant Hurricane Delta 
over the northwestern Caribbean Sea has weakened the ridge that had 
been steering Norbert. Therefore, the forecast track through 48 h 
is more uncertain than usual given the potential for erratic motion 
as indicated by the diverging model solutions. By Friday, Norbert 
should begin moving slowly westward or west-northwestward as the 
ridge gradually builds to the north. The NHC track forecast remains 
fairly close to the various consensus aids.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  07/0900Z 14.0N 107.1W   35 KT  40 MPH
 12H  07/1800Z 13.9N 107.2W   35 KT  40 MPH
 24H  08/0600Z 13.9N 107.3W   35 KT  40 MPH
 36H  08/1800Z 14.0N 107.6W   35 KT  40 MPH
 48H  09/0600Z 14.0N 108.0W   35 KT  40 MPH
 60H  09/1800Z 14.1N 108.7W   35 KT  40 MPH
 72H  10/0600Z 14.6N 109.5W   35 KT  40 MPH
 96H  11/0600Z 15.5N 111.0W   35 KT  40 MPH
120H  12/0600Z 16.5N 112.5W   35 KT  40 MPH
 
$$
Forecaster Reinhart/Stewart
 
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