Issued at 900 PM MDT Sat Sep 12 2020
000
WTPZ41 KNHC 130238
TCDEP1
Tropical Depression Sixteen-E Discussion Number 1
NWS National Hurricane Center Miami FL EP162020
900 PM MDT Sat Sep 12 2020
The last few visible satellite images indicated convection growing
closer to the center of a low pressure area that NHC has been
tracking for the past few days. Since the low was already
well-defined this afternoon, the development of organized deep
convection means that a tropical depression has formed. The initial
wind speed is set to 30 kt, which is a blend of the TAFB/SAB fixes
and earlier ASCAT data. The depression is embedded within a
moderate easterly wind-shear environment, partially related to its
position in the larger ITCZ/monsoon trough structure. Global model
guidance is in reasonable agreement on the large-scale circulation
becoming focused on the new tropical cyclone and a slight relaxation
of the shear during the next couple of days. This change should
lead to gradual intensification, and the new forecast is between the
model consensus and the corrected-consensus aids. Beyond 2-3 days,
decreasing SSTs and increasing dry air entrainment should promote
weakening, and that is reflected below.
The initial motion estimate is an uncertain northwestward or 315/08
kt. A mid-level ridge is forecast to build westward, causing the
cyclone to move west-northwestward for a few days after the weekend.
A westward turn is forecast at long range due to the shallow
cyclone feeling the low-level ridge. One big uncertainty with this
forecast is how it interacts with the larger ITCZ/monsoon trough
circulation, including the remnants of Invest 91E. For now, it is
assumed that only a slight slow down occurs as the depression
becomes the dominant circulation in the area, and the forecast is
more consistent with the GFS- or UKMET-based guidance. However, a
slower ECMWF-like solution is also possible, but is being given less
weight at this time.
FORECAST POSITIONS AND MAX WINDS
INIT 13/0300Z 16.7N 112.9W 30 KT 35 MPH
12H 13/1200Z 17.5N 113.8W 35 KT 40 MPH
24H 14/0000Z 18.3N 115.4W 40 KT 45 MPH
36H 14/1200Z 18.9N 116.9W 45 KT 50 MPH
48H 15/0000Z 19.5N 118.5W 50 KT 60 MPH
60H 15/1200Z 20.0N 119.9W 55 KT 65 MPH
72H 16/0000Z 20.5N 121.0W 55 KT 65 MPH
96H 17/0000Z 21.5N 123.5W 45 KT 50 MPH
120H 18/0000Z 21.5N 126.0W 30 KT 35 MPH
$$
Forecaster Blake