Eastern Pacific Basin Tropical Cyclones

Tropical Storm Pamela Forecast Discussion


000
WTPZ41 KNHC 112056
TCDEP1

Tropical Storm Pamela Discussion Number   7
NWS National Hurricane Center Miami FL       EP162021
300 PM MDT Mon Oct 11 2021

Entrainment of dry mid-level air along with some modest 
north-northwesterly mid-level shear has caused Pamela's low-level 
circulation to become slightly exposed just northwest of the 
somewhat ragged inner-core convection. Upper-level outflow, however, 
has improved in all quadrants, with a narrow equatorward outflow 
channel having developed in the eastern semicircle since the 
previous advisory. Pamela's intensity was increased to 60 kt at 
1800 UTC based on satellite current-intensity estimates of T4.0/65 
kt from TAFB and T3.7/59 kt from UW-CIMSS ADT. However, 60 kt might 
be a little generous at the 2100 UTC advisory time, given that the 
low-level center has recently become partially exposed.

The motion estimate is northwestward or 320/06 kt. There is no 
significant change to the previous forecast track or reasoning. This 
current slow northwestward motion should continue this afternoon and 
evening as Pamela approaches the western periphery of a deep-layer 
subtropical ridge. Later tonight, the cyclone is expected to turn 
slowly northward, followed by a faster northeastward motion by 
Tuesday night as Pamela gets caught up in moderate southwesterly 
flow ahead of a deep-layer mid-latitude trough approaching from the 
northwest and west. This developing flow pattern is depicted quite 
well by all of the global and regional models, and should result in 
Pamela accelerating northeastward on Wednesday right up until the 
storm makes landfall along the west-central coast of Mexico. The new 
NHC forecast track has been shifted a little to the right again, 
and is close to the middle of the tightly packed TCVE, GFEX, 
NOAA-HCCA, and FSSE consensus track-model envelope.

The global and regional models are in very good agreement that the 
current slight southeastward tilt to the vortex column should abate 
within the next 6 hours or so, along with the dry mid-level air 
mixing out. As a result, deep convection should re-fire near the 
center later tonight, resulting in the development of an eyewall, 
which will create the necessary chimney effect to allow Pamela to 
resume its earlier rapid intensification trend. In fact, all of the 
models now show strengthening right up until the cyclone makes 
landfall on Wednesday due to the upper-level outflow pattern 
expanding, along with the development of poleward and equatorward 
outflow channels by late Tuesday. The new official intensity 
forecast is basically the same as the previous advisory, and lies 
near the upper-end of the intensity guidance. Pamela is still 
expected to become a dangerous major hurricane prior to landfall.  
After landfall occurs, rapid weakening is forecast due to the 
cyclone moving over the rugged terrain of west-central Mexico. 
However, the higher elevations of north-central Mexico could still 
receive tropical-storm force winds after Pamela moves well inland. 
Furthermore, deep moisture associated with Pamela will gradually 
overspread much of north-central and northeastern Mexico late on 
Wednesday, and then move into southern and central Texas on 
Thursday, enhancing the rainfall potential in those areas.

An Air Force Reserve Hurricane Hunter aircraft is scheduled to
investigate Pamela on Tuesday during the late morning and early 
afternoon to provide a better estimate of the cyclone's intensity.


Key Messages:

1. Pamela is forecast to be a major hurricane when it reaches the
coast of west-central mainland Mexico on Wednesday, and
life-threatening storm surge and dangerous hurricane-force winds are
possible within the Hurricane Watch area.  Residents in this area
should monitor the progress of Pamela and follow any advice given by
local officials.

2. Pamela is expected to pass near or south of the southern tip of
the Baja California peninsula as a hurricane Tuesday night and early
Wednesday, and tropical-storm conditions are possible within the
Tropical storm Watch area.

3. Heavy rains associated with Pamela are expected to move into the 
Mexican States of Sinaloa and western Durgano along with southern 
portions of Baja California Sur Tuesday and Wednesday. This will 
pose a threat of significant and life-threatening flash flooding and 
mudslides.

4. Heavy rains associated with Pamela are expected across portions 
of central Texas and southeastern Oklahoma late Wednesday and 
Thursday.  This may result in flash and urban flooding.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 17.2N 108.5W   60 KT  70 MPH
 12H  12/0600Z 18.3N 109.0W   70 KT  80 MPH
 24H  12/1800Z 20.0N 108.9W   85 KT 100 MPH
 36H  13/0600Z 22.0N 107.8W  100 KT 115 MPH
 48H  13/1800Z 24.3N 105.8W   45 KT  50 MPH...INLAND
 60H  14/0600Z 27.4N 102.1W   30 KT  35 MPH...POST-TROP/INLAND
 72H  14/1800Z 31.2N  97.7W   20 KT  25 MPH...POST-TROP/INLAND
 96H  15/1800Z...DISSIPATED INLAND

$$
Forecaster Stewart



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