Tropical Depression Nine-E Forecast Discussion

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Tropical Depression Nine-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP092024
800 AM MST Thu Sep 12 2024

Geostationary satellite imagery indicates that the growing area of
deep convection associated with the low pressure system off the
coast of west-central Mexico has been quite persistent with
increased banding noted over the past 6 to 12 h.  The subjective
intensity estimate from TAFB is T-2.0/30 kt, and on this basis, the
system is upgraded to a 30-kt tropical depression.

The initial motion is an uncertain northwest, or 325/6 kt.  There is
a fair amount of uncertainty in the initial position of the center,
but it appears to be near the eastern edge of the convection, based
on recent microwave imagery.  A deep-layer trough located over the
western United States will steer the cyclone toward the
north-northwest over the next 24 to 36 h, bringing the system near
the southern portion of Baja California Sur. After that time, the
deep-layer trough is forecast to weaken, which should cause
steering currents to weaken.  This pattern will likely induce a
slower motion toward the north, likely over the waters of
the southern Gulf of California.  The cyclone could approach the
coast of northern Sinaloa or Sonora Saturday night into Sunday.
The track forecast guidance is in good agreement for the first
48 h, but then starts to diverge a bit while the system is over the
southern Gulf of California. The NHC track forecast is near the
middle of the guidance envelope.  Due to some uncertainty in the
track beyond that time, coastal residents of the Mexican states of
Sinaloa and Sonora should continue to monitor the progress of this
system.

Tropical Depression Nine-E is currently located within an
environment of warm ocean waters, low to moderate vertical wind
shear, and within a fairly moist low- to mid-level troposphere.
However, very dry air is evident on water vapor imagery to the
northwest of the cyclone.  These conditions are unlikely to change
before the cyclone reaches Baja California Sur, and the NHC
forecast shows the system becoming a tropical storm later today.
Land interaction with the peninsula should cause some temporary
weakening.  However, water temperatures in the Gulf of California
are quite warm, so some restrengthening is possible after the
cyclone emerges back over water.  The NHC intensity forecast is
near the higher end of the intensity guidance.  Beyond 60 h,
westerly wind shear is expected to increase while the cyclone moves
into a drier environment.  Even if the system is still over water
at that time, the cyclone is likely to begin weakening.  The GFS
and ECMWF simulated satellite imagery products show the cyclone
losing its convection around 72 h.  The NHC forecast shows
weakening at that time, with the system becoming a remnant low
beyond 72 h.

Key Messages:
1. Tropical Depression Nine-E will bring heavy rainfall to portions 
of western Mexico and southern Baja California through this weekend. 
This heavy rainfall will bring a risk of flash flooding and 
mudslides to portions of the area. 

2. Tropical storm conditions are expected to begin in portions of 
the Baja California Sur on Friday, where Tropical Storm Warnings 
have been issued. 


FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 19.2N 107.6W   30 KT  35 MPH
 12H  13/0000Z 20.4N 108.4W   35 KT  40 MPH
 24H  13/1200Z 22.0N 109.5W   40 KT  45 MPH
 36H  14/0000Z 23.5N 110.2W   45 KT  50 MPH
 48H  14/1200Z 25.0N 110.1W   45 KT  50 MPH
 60H  15/0000Z 26.1N 110.0W   45 KT  50 MPH
 72H  15/1200Z 27.0N 110.2W   35 KT  40 MPH
 96H  16/1200Z 28.6N 111.2W   25 KT  30 MPH...POST-TROP/INLAND
120H  17/1200Z...DISSIPATED

$$
Forecaster Hagen

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