Tropical Storm RENE Advisory ma, 07-09

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Tropical Depression Eighteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL182020
800 AM CVT Mon Sep 07 2020

Shower and thunderstorm activity associated with the area of low
pressure over the far eastern Atlantic has continued to increase and
become organized in a band overnight.  First light visible satellite
imagery suggests that the circulation has also become better
defined.  Based on the above, advisories are being initiated on a
new tropical depression, the eighteenth of the 2020 Atlantic
hurricane season.  Dvorak satellite estimates from both TAFB and SAB
support an intensity of 25 kt, but given the continued improvement
in organization the initial winds are set at 30 kt for this
advisory.  ASCAT data later this morning should provide additional
information on the intensity of the cyclone.

The depression lies within a favorable upper-level environment and
the SHIPS guidance indicates that the vertical wind shear will
remain 10 kt or less over the next few days while the depression
traverses sea surface temperatures of around 27 degrees Celsius.
These conditions, along with a moist mid-level atmosphere should
allow for steady strengthening over the next few days, and the NHC
forecast calls for the system to become a tropical storm later
today, and a hurricane in about 72 hours.  After that time, the
cyclone is forecast to pass over slightly cooler waters and the
global models depict an increase in southwesterly upper-level flow
over the system by the end of the period.  These less conducive
factors are expected to slow the intensification process toward the
end of the period. The NHC intensity forecast is a blend of the
IVCN multi-model consensus and the HFIP corrected consensus.

The initial motion of the depression is a somewhat uncertain
280/10 kt.  A narrow mid-level ridge to the north of the depression
is forecast to build westward over the next few days which is
expected to steer the system westward to west-northwestward, and
the track guidance is in good agreement through 72 hours.  After
that time, a weakness is forecast to develop in the ridge near 40
degrees west, and the cyclone is expected to turn
west-northwestward and then northwestward between the ridge to its
northeast and Tropical Depression Seventeen to its southwest.  Since
there could be some binary interaction between the two tropical
cyclones later in the period, the longer range track guidance is
not in as good of agreement, and there is more uncertainty than
average in the long-range track forecast.

Key Messages:

1. The depression is forecast to strengthen into a tropical storm
later today and tropical storm conditions are expected to spread
over portions of the Cabo Verde Islands later today and tonight.  A
Tropical Storm Warning is in effect for those islands.

2. The depression is expected to bring locally heavy rainfall to
portions of the Cabo Verde Islands through Tuesday morning.



FORECAST POSITIONS AND MAX WINDS

INIT  07/0900Z 15.2N  20.3W   30 KT  35 MPH
 12H  07/1800Z 15.6N  22.0W   35 KT  40 MPH
 24H  08/0600Z 16.0N  24.5W   40 KT  45 MPH
 36H  08/1800Z 16.4N  27.3W   50 KT  60 MPH
 48H  09/0600Z 16.8N  30.2W   55 KT  65 MPH
 60H  09/1800Z 17.4N  32.9W   60 KT  70 MPH
 72H  10/0600Z 18.1N  35.5W   65 KT  75 MPH
 96H  11/0600Z 19.7N  39.6W   70 KT  80 MPH
120H  12/0600Z 22.4N  43.2W   70 KT  80 MPH

$$
Forecaster Brown