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Tropical Depression Eighteen-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP182020
300 AM MDT Tue Sep 29 2020
 
A burst of deep convection that developed near the center of the 
area of low pressure well southwest of the southwestern coast of 
Mexico during the evening has persisted overnight.  Microwave 
imagery and a 0444 UTC ASCAT-C overpass indicated that the center 
of the low re-formed within the area of deep convection and with 
the overall increase in the organization of the system, advisories 
are being initiated on the eighteen tropical depression of the 2020 
eastern Pacific hurricane season.  The scatterometer data revealed 
peak winds of around 30 kt, and that is used as the advisory 
intensity.  

The depression is located over warm water and within an area of 
light to moderate northeasterly shear, and these conditions are 
expected to allow for steady strengthening over the next few days.  
Although the SHIPS model guidance only shows a peak intensity 
of 65-70 kt in 72-84 hours, the SHIPS rapid intensification index 
indicates a 50 percent chance of a 65 kt increase in intensity over 
the next 72 hours. In addition, the global models significantly 
deepen the system over the next few days. On the basis of the 
SHIP RI information and the global models, the NHC intensity 
forecast is above the IVCN intensity consensus close to the more 
aggressive HWRF and HCCA models.  Late in the period, decreasing 
SSTs and increasing vertical wind shear should result in weakening. 

Given the recent re-formation of the center, the initial motion 
estimate is a highly uncertain 275/9 kt. A deep-layer ridge 
centered over the southwestern United States is expected to steer 
the cyclone westward to west-northwestward during the next several 
days.  By the end of the forecast period, the cyclone will be 
approaching the southwestern portion of the ridge allowing it to 
turn northwesterly.  Although there some model differences in 
the predicted forward speed of the depression, the models are in 
good agreement on the overall track forecast scenario.  To account 
for these forward speed differences, the NHC forecast is near the 
middle of the guidance envelope close to the various consensus 
aids. 


FORECAST POSITIONS AND MAX WINDS
 
INIT  29/0900Z 13.2N 107.6W   30 KT  35 MPH
 12H  29/1800Z 13.5N 109.0W   35 KT  40 MPH
 24H  30/0600Z 14.2N 111.2W   45 KT  50 MPH
 36H  30/1800Z 14.6N 114.3W   55 KT  65 MPH
 48H  01/0600Z 14.8N 117.3W   65 KT  75 MPH
 60H  01/1800Z 15.3N 119.9W   75 KT  85 MPH
 72H  02/0600Z 16.2N 122.3W   85 KT 100 MPH
 96H  03/0600Z 18.3N 126.2W   80 KT  90 MPH
120H  04/0600Z 20.5N 129.2W   60 KT  70 MPH
 
$$
Forecaster Brown
 
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