[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 090251
TCDAT3

Tropical Depression Rene Discussion Number   8
NWS National Hurricane Center Miami FL       AL182020
200 AM CVT Wed Sep 09 2020

Rene's circulation remains fairly robust based on a 08/2148Z ASCAT-A
overpass. However, the overall convective pattern has eroded
significantly, and this is reflected in the ASCAT scatterometer wind
data only showing surface winds of about 25 kt. Allowing for some
undersampling, plus a recent increase in convection near the
center, the intensity has only been lowered to 30 kt for this
advisory. Rene remains beneath a pronounced upper-level anticyclone
and outflow is fairly symmetrical in all quadrants.

The initial motion is 285/14 kt. There continues to be no
significant change to previous forecast track or reasoning. Rene is
expected to move generally west-northwestward around the
southwestern periphery of a deep-layer ridge for the next couple of
days, followed by a decrease in forward speed and a turn toward the
northwest on Friday and a motion toward the north on Saturday and
Sunday. The latest NHC model guidance is in decent agreement on
this developing steering flow pattern, thus the new NHC track
forecast is essentially just an extension of the previous advisory
track and lies close to a blend of the consensus models TVCA, GFEX,
and NOAA-HCCA.

Although Rene has weakened, a burst of strong convection with cloud
tops colder than -80C has developed over and to the west of the
center, while a fragmented band of convection has formed in the
northern semicircle. These features strongly suggest that Rene is
poised to restrengthen soon. Sea-surface temperatures are expected
to be 26.0-26.5 deg C in the 24-60 h period, which are only marginal
for strengthening to occur. However, mid-level humidity values are
forecast to be near 70 percent and the cyclone is expected to remain
under a favorable upper-level anticyclone during that time.  Given
these factors, slow but steady intensification is forecast, with
Rene still expected to become a hurricane in 2-3 days.  Thereafter,
strong westerly to west-northwesterly vertical wind shear in excess
of 25-30 kt is expected to cause Rene to weaken significantly on
days 4 and 5. The new official intensity forecast is similar to but
slightly lower than the previous intensity forecast, and is along
the extreme upper portion of the guidance envelope and is above the
intensity consensus models.


FORECAST POSITIONS AND MAX WINDS

INIT  09/0300Z 17.0N  29.3W   30 KT  35 MPH
 12H  09/1200Z 17.5N  31.1W   35 KT  40 MPH
 24H  10/0000Z 18.4N  33.7W   40 KT  45 MPH
 36H  10/1200Z 19.3N  35.9W   50 KT  60 MPH
 48H  11/0000Z 20.5N  38.1W   60 KT  70 MPH
 60H  11/1200Z 22.1N  39.8W   65 KT  75 MPH
 72H  12/0000Z 24.2N  41.4W   60 KT  70 MPH
 96H  13/0000Z 28.5N  42.6W   50 KT  60 MPH
120H  14/0000Z 30.2N  40.3W   40 KT  45 MPH

$$
Forecaster Stewart
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