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Tropical Depression Seven-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP072021
900 AM MDT Sat Jul 17 2021
 
The broad low pressure system that the NHC has been monitoring for 
the past few days well offshore the southwestern coast of Mexico 
has finally developed enough organized deep convection and a 
well-defined inner-core wind field to be classified as a tropical 
depression. The initial intensity is estimated to be 30 kt, which is 
a little below the consensus T2.5/35-kt classifications from TAFB 
and SAB.

The initial motion estimate is an uncertain 295/15 kt due to the 
lack of a well-defined center prior to 1200 UTC. Regardless, the 
global and regional models are in exceptionally good agreement on 
the cyclone moving west-northwestward today, and then turning toward 
the west by late tonight or early Sunday, with that general motion 
continuing through 72 hours. Thereafter, the deep-layer subtropical 
ridge to the north that will steer the system for the next 5 days is 
expected to build slightly southward, nudging the cyclone on a 
west-southwestward track at 96 and 120 hours. The NHC forecast track 
lies close to but a little slower than the various consensus models 
out of respect for the slower GFS and GFS-ensemble models, which are 
forecasting a stronger and, thus, more vertically deep tropical 
cyclone that should move slower compared to the other weaker models.

During the next 48 hours or so, the cyclone is expected to remain 
embedded within an environment conducive for strengthening, 
characterized by light wind shear (<10 kt), sea-surface temperatures 
(SST) above 27 deg C, and deep moisture through the low- to 
mid-levels of the troposphere. Furthermore, a large upper-level low 
located just west of the Baja California peninsula, which has been 
enhancing the poleward outflows of this disturbance and Hurricane 
Felicia farther to the west, is forecast to persist for at least the 
next couple of days. All of these favorable conditions argue for at 
least modest strengthening during that time, with the only hindering 
factor being the large size of the system's circulation. Thereafter, 
the cyclone will move over sub-26C SSTs, which should act to cap the 
intensification process despite the low vertical wind shear 
conditions that are expected to persist. However, the rate of 
weakening is forecast to be a little slower than normal due to the 
southern half of the circulation remaining over warmer waters, which 
will provide warm moist inflow to help fuel thunderstorms near the 
inner-core. The NHC intensity forecast closely follows the NOAA-HCCA 
consensus model through 60 hours, and then is a little above all of 
the consensus models thereafter.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/1500Z 16.8N 109.2W   30 KT  35 MPH
 12H  18/0000Z 17.3N 110.8W   40 KT  45 MPH
 24H  18/1200Z 17.9N 112.8W   45 KT  50 MPH
 36H  19/0000Z 18.2N 115.1W   50 KT  60 MPH
 48H  19/1200Z 18.3N 117.5W   55 KT  65 MPH
 60H  20/0000Z 18.5N 120.0W   55 KT  65 MPH
 72H  20/1200Z 18.5N 122.6W   50 KT  60 MPH
 96H  21/1200Z 18.2N 127.7W   40 KT  45 MPH
120H  22/1200Z 17.9N 132.9W   35 KT  40 MPH
 
$$
Forecaster Stewart
 
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