Tropical Depression Gordon Forecast Discussion Number 24

By | September 17, 2024

000
WTNT42 KNHC 170845
TCDAT2

Tropical Depression Gordon Discussion Number  24
NWS National Hurricane Center Miami FL       AL072024
500 AM AST Tue Sep 17 2024

After becoming a bit better organized Monday evening with persistent 
deep convection over the low-level center, Gordon's convective 
organization has been steady during the overnight hours. Subjective 
Dvorak intensity estimates range from 25-35 kt, while recent 
objective estimates from UW-CIMSS are in the 31-36 kt range. Based 
on these intensity estimates as well as taking into account earlier 
ASCAT data, Gordon's intensity is held at 30 kt for this advisory.

The ASCAT passes Monday evening helped locate the center, but the 
center has been difficult to find since that time.  Recent satellite 
images suggest that the center may be near the northern edge of the 
central convective area.  The motion is still estimated to be 
westward, or 265/3 kt, but models indicate that the northward turn 
should begin within the next few hours.  A frontal low currently 
located several hundred miles north of Gordon has created a weakness 
in the subtropical ridge, which will induce a northward and then a 
north-northeastward motion at an increasing forward speed during the 
next couple of days.  Gordon should pass east of this feature 
Wednesday night or Thursday as it is steered by mid-level high 
pressure to the east of the cyclone.  Some of the global models show 
this ridge building to the northeast of Gordon, which could cause 
Gordon to bend more toward the north in 4 to 5 days.  There are 
significant speed differences as well as cross-track spread at days 
4 and 5.  The new NHC forecast is similar to the previous one 
through 48 h, but is nudged to the west of the previous official 
forecast beyond 48 h, closer to the latest consensus aids.  During 
the 3 to 5 day time period, the NHC forecast is slower than the 
latest GFS model and well to the east of the latest ECMWF global 
model.

Gordon's intensity forecast is challenging.  Environmental 
conditions appear moist enough for Gordon to at least maintain its 
intensity during the next couple of days, given the weak vertical 
wind shear and warm sea-surface temperatures.  However, global 
models do not show Gordon intensifying much during the next couple 
of days as the cyclone interacts with a weakening non-tropical low, 
currently located north of Gordon.  Some strengthening is likely 
once Gordon moves past this feature, but there is quite a bit of 
uncertainty in what the upper-level winds will look like over the 
cyclone in the day 3 to 5 period.  The GFS model shows moderate 
southwesterly shear during that time, whereas the ECMWF and other 
global models suggest stronger shear from the west or northwest, 
which would be a less favorable direction and would likely prevent 
further strengthening.  As a result, there is a large spread in the 
intensity guidance, leading to below average confidence in the NHC 
intensity forecast.  The NHC intensity forecast is similar to the 
previous one, and remains near the low end of the intensity guidance 
through the forecast period.


FORECAST POSITIONS AND MAX WINDS

INIT  17/0900Z 19.0N  49.0W   30 KT  35 MPH
 12H  17/1800Z 19.5N  49.1W   30 KT  35 MPH
 24H  18/0600Z 20.4N  48.7W   30 KT  35 MPH
 36H  18/1800Z 21.7N  48.2W   30 KT  35 MPH
 48H  19/0600Z 23.3N  47.5W   35 KT  40 MPH
 60H  19/1800Z 25.1N  46.7W   45 KT  50 MPH
 72H  20/0600Z 26.3N  45.8W   50 KT  60 MPH
 96H  21/0600Z 27.6N  44.6W   50 KT  60 MPH
120H  22/0600Z 30.0N  44.3W   55 KT  65 MPH

$$
Forecaster Hagen

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