Eastern Pacific Basin Tropical Cyclones

Tropical Depression Eighteen-E Forecast Discussion


000
WTPZ43 KNHC 051455
TCDEP3

Tropical Depression Eighteen-E Discussion Number   5
NWS National Hurricane Center Miami FL       EP182021
1000 AM CDT Fri Nov 05 2021

The convective structure with the depression this morning remains 
disheveled, with only scattered convection pulsing around the 
circulation without much organization. The latest subjective Dvorak 
satellite estimates are T2.0/30 kt from TAFB and T1.5/25 kt from 
SAB, while the most recent UW-CIMSS ADT estimate was T2.1/31 kt. A 
blend of these data support maintaining the intensity at 30 kt this 
advisory.

Early morning visible satellite imagery suggests that the system is 
moving south of due west, with the latest motion estimate at 260/8 
kt. As an amplified short-wave trough located over the Gulf of 
Mexico propagates eastward, a mid-level ridge ridge centered near 
the Baja California peninsula is expected to expand eastward over 
Mexico. This feature should dominate the steering pattern over the 
depression through the forecast period, leading to a general 
westward motion but at a gradually accelerating forward speed. 
Because the depression is quite shallow currently, low-level flow in 
association with a developing gale-force gap wind event in the Gulf 
of Tehuantepec may also assist the system in losing a bit more 
latitude over the next 24-36 hours. After 48 hours, a weakness under 
the ridge from an downstream disturbance may allow the depression to 
gain back a bit of latitude. The track guidance remains in fairly 
good agreement, though differences in speed are seen between the 
slower GFS versus the faster ECMWF guidance, and another southward 
shift has taken place. The official NHC track forecast is a bit 
further south and a touch faster compared to the previous one, 
following the consensus aids TVCE and HCCA.

The current poor organization of the convection argues against any 
short-term intensity changes. While deep-layer (200-850 hPa) 
vertical wind shear is expected to remain low, higher mid-level 
shear may prevent better convective organization over the next 36-48 
hours. While mid-level relative humidity is forecast to be 
sufficently moist, visible satellite imagery suggests stable 
stratocumulus inflow from the south, while the aforementioned gap 
wind event to the north may also contribute to a less-than-optimal 
thermodynamic environment. The official NHC intensity forecast now 
shows no intensification over the next 36 hours with only gradual 
intensification thereafter, favoring the more pessimistic guidance. 
If the latest ECMWF and LGEM guidance are correct, the depression 
may fail to intensify at all over the forecast period.


FORECAST POSITIONS AND MAX WINDS

INIT  05/1500Z  9.4N  92.4W   30 KT  35 MPH
 12H  06/0000Z  9.2N  93.5W   30 KT  35 MPH
 24H  06/1200Z  8.9N  95.4W   30 KT  35 MPH
 36H  07/0000Z  8.7N  97.5W   30 KT  35 MPH
 48H  07/1200Z  8.7N  99.7W   35 KT  40 MPH
 60H  08/0000Z  9.2N 102.0W   40 KT  45 MPH
 72H  08/1200Z  9.8N 104.4W   45 KT  50 MPH
 96H  09/1200Z 10.9N 109.4W   50 KT  60 MPH
120H  10/1200Z 11.3N 114.2W   55 KT  65 MPH

$$
Forecaster Papin



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