ZCZC MIATCDEP4 ALL
TTAA00 KNHC DDHHMM
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
NNNN