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Tropical Storm Norbert Discussion Number 5
NWS National Hurricane Center Miami FL EP192020
300 PM MDT Tue Oct 06 2020
A compact central dense overcast with cloud tops occasionally
cooling to -80 degrees C has persisted over the center of Norbert
throughout the day. A recent ASCAT overpass showed peak winds of 41
kt near the center of storm. However, due to the small size of the
cyclone, the highest winds are likely not being sampled. Therefore,
the initial intensity is being raised to 45 kt, and this is in good
agreement with the latest Dvorak CI values from TAFB and SAB.
Norbert is expected to remain in an environment of low vertical wind
shear while over very warm waters for the next couple of days.
Despite the positive environmental factors in the near term, model
guidance is in poor agreement on the future intensity of Norbert.
The spread in the forecast intensity has widened even further today,
with most of the global and hi-resolution dynamical models
weakening the system over the next few days, while the SHIPS and
LGEM guidance favor slow strengthening. Since the SHIPS guidance
has been the most accurate for Norbert's intensity thus far, the
latest NHC forecast is close to, but just below the SHIPS guidance
values through 48 h. After 48 h, the shear is expected to become
moderate, and there are indications that subsidence will increase
over the cyclone. These negative environmental factors should
inhibit further intensification, and could cause the cyclone to
weaken.
The steering currents around Norbert are collapsing, as the
mid-level ridge over southern Mexico dissipates in response to
Hurricane Delta over the northwestern Caribbean Sea. Model tracks
diverge by a few hundred miles in varying directions while the
steering flow is weak. The consensus guidance is in between these
solutions and shows very little movement for the next 72 h. By late
this week, a weak mid-level ridge should build north of the cyclone,
which would result in a slow west-northwestward to westward motion.
The latest NHC track forecast remains close to the various consensus
aids.
FORECAST POSITIONS AND MAX WINDS
INIT 06/2100Z 14.4N 106.6W 45 KT 50 MPH
12H 07/0600Z 14.5N 106.7W 50 KT 60 MPH
24H 07/1800Z 14.5N 106.7W 50 KT 60 MPH
36H 08/0600Z 14.5N 106.7W 55 KT 65 MPH
48H 08/1800Z 14.5N 106.7W 55 KT 65 MPH
60H 09/0600Z 14.5N 107.2W 50 KT 60 MPH
72H 09/1800Z 14.8N 108.0W 50 KT 60 MPH
96H 10/1800Z 15.5N 110.1W 50 KT 60 MPH
120H 11/1800Z 16.0N 112.0W 50 KT 60 MPH
$$
Forecaster Latto
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