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Tropical Depression Fifteen-E Discussion Number 3
NWS National Hurricane Center Miami FL EP152021
300 AM MDT Wed Sep 08 2021
The circulation of the depression has continued to become better
defined, and there has been a substantial increase in deep
convection within bands to the north and northeast of the center.
However, the inner core remains slightly displaced from this
activity, and a combination of subjective and objective intensity
estimates supports maintaining the cyclone as a 30-kt depression
for this advisory.
The system has either been meandering or its center re-formed
yesterday, and the long-term motion is a drift toward the
north-northwest (335 degrees) at about 3 kt. This motion is likely
due to the depression being caught within weak steering currents
between a mid-level low west of the Baja California peninsula and
troughing extending across Mexico to the Gulf of Mexico. A strong
mid-tropospheric high over the western United States should
gradually cause the system to move faster toward the northwest
during the next 2 to 3 days, bringing it very close to Baja
California Sur in about 48 hours. Of the track models, the GFS and
COAMPS-TC models are the solutions which bring the cyclone's center
closest to Baja California Sur, while the ECMWF and UKMET models
have the farther-offshore tracks. The new NHC track forecast
splits the difference among these solutions and is a little east
of the previous forecast during the first 36 hours to account for
recent short-term motions. After 36 hours, it falls more or less
in line with the previous prediction and is very close to the
consensus aids, HWRF, and HMON.
There are counteracting factors at play regarding the depression's
future intensity. Although deep-layer shear is forecast to be low,
the GFS suggests that moderate to strong mid-level shear could
develop below the outflow level during the next 24-48 hours. Sea
surface temperatures will be plenty warm for strengthening during
the next 48 hours, yet upper-level divergence is not expected to be
ideal. Since the system's circulation appears to be improving,
steady strengthening is forecast during the first 48 hours, and the
depression could become a short-lived hurricane while it passes the
Baja California peninsula. This forecast is near the upper end
of the guidance envelope, close to the GFS, HWRF, COAMPS-TC, and
HCCA solutions. The cyclone will be moving over colder waters in
2-3 days, which should cause quick weakening and a degeneration to
remnant low status by day 4.
Key Messages:
1. Tropical Depression Fifteen-E is expected to strengthen to a
tropical storm later today, and it could become a short-lived
hurricane while it passes just to the southwest of southern
portions of Baja California Sur Thursday and Friday. A Tropical
Storm Watch is in effect for southern portions of Baja California
Sur, and interests there should continue to monitor the progress of
the depression.
2. Heavy rains associated with Tropical Depression Fifteen-E are
possible across southern portions of Baja California Sur Thursday
through Friday. This will pose a threat of flash flooding and
mudslides.
FORECAST POSITIONS AND MAX WINDS
INIT 08/0900Z 18.5N 107.1W 30 KT 35 MPH
12H 08/1800Z 19.1N 107.6W 40 KT 45 MPH
24H 09/0600Z 20.0N 108.4W 50 KT 60 MPH
36H 09/1800Z 21.1N 109.6W 60 KT 70 MPH
48H 10/0600Z 22.3N 111.2W 65 KT 75 MPH
60H 10/1800Z 23.3N 112.8W 55 KT 65 MPH
72H 11/0600Z 23.9N 114.5W 45 KT 50 MPH
96H 12/0600Z 24.1N 117.1W 30 KT 35 MPH...POST-TROP/REMNT LOW
120H 13/0600Z 23.6N 119.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
$$
Forecaster Berg
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