Eastern Pacific Basin Tropical Cyclones

Hurricane Pamela Forecast Discussion


000
WTPZ41 KNHC 121442
TCDEP1

Hurricane Pamela Discussion Number  10
NWS National Hurricane Center Miami FL       EP162021
900 AM MDT Tue Oct 12 2021

Similar to this time yesterday, Pamela is undergoing an episodic 
convective bursting phase.  The convection is likely being modulated 
by west-northwesterly mid-level shear of at least 15 kt that is 
undercutting the outflow layer, plus intrusions of dry mid-level air 
with humidity values near 55 percent, as analyzed in SHIPS 
diagnostics. The intensity at 1200 UTC was increased to 70 kt based 
on an average of subjective Dvorak satellite classifications of 
T4.5/77 kt from TAFB and T4.0/65 kt from SAB, and an objective 
estimate of 70 kt from UW-CIMSS ADT. An Air Force Reserve 
reconnaissance aircraft is currently en route to investigate 
Pamela's structure, intensity, and wind field.

Pamela is moving northward or 010/11 kt. The hurricane is now on or 
just north of the east-west-oriented axis of a deep-layer 
subtropical ridge situated over central Mexico. The northward 
motion should continue this morning, followed by a turn toward the 
northeast by this afternoon or early evening as Pamela becomes 
embedded within southwesterly environmental flow ahead of a broad 
mid-/upper-level trough. That large-scale feature will cause the 
hurricane to accelerate tonight through Wednesday, with Pamela now 
expected to reach the coast of west-central Mexico just before 1200 
UTC Wednesday morning. After the hurricane moves inland early 
Wednesday, Pamela, or its remnants should continue to accelerate 
northeastward across central and northern Mexico and into Texas by 
the end of the week. The latest NHC model guidance is tightly 
packed around the previous advisory forecast track, so no 
significant changes were required.

The latest GFS- and ECMWF-based SHIPS intensity models output show 
that west-northwesterly 850-200-mb shear of at least 15 kt is 
allegedly affecting Pamela. However, shear analyses from UW-CIMSS 
indicate that the shear is less than 10 kt from the west. Once 
Pamela makes the northeastward turn, the deep-layer shear vector is 
forecast to back around to a southwesterly direction and become 
aligned with the hurricane's forward motion, which should help to
lessen the negative effects of the vertical wind shear. Although 
the mid-level moisture is expected to be somewhat austere at only 
50-55 percent, Pamela will be moving over sea-surface temperatures 
(SST) near 31 deg C, which is almost 1 deg C warmer than current SST 
values beneath the hurricane. This expected increase in ocean heat 
content, along with decreasing shear, should enhance the convective 
bursting phase that Pamela will likely undergo later tonight during 
the nocturnal convective maximum period, enabling the cyclone to 
strengthen to near major hurricane status before landfall occurs. 
The new NHC intensity forecast continues to indicate steady to 
rapid strengthening, and remains above all of the available 
intensity guidance. After landfall, Pamela is expected to rapidly 
decay due to interaction with the mountainous terrain of Mexico, 
with the cyclone ultimately dissipating over northern Mexico in 2 
to 3 days. Another aircraft reconnaissance mission to investigate 
Pamela is scheduled for tonight at 0530 UTC.

Although the cyclone is forecast to dissipate over the rugged 
terrain of Mexico, deep moisture associated with the system's 
remnants are likely to spread over north-central and northeastern 
Mexico on Wednesday, and then move into portions of the 
south-central United States late Wednesday or Thursday.

Key Messages:

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

2. Pamela is expected to pass south of the southern tip of the Baja
California peninsula as a hurricane later today and tonight, 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  12/1500Z 20.4N 108.9W   70 KT  80 MPH
 12H  13/0000Z 21.8N 108.3W   85 KT 100 MPH
 24H  13/1200Z 24.1N 106.4W   65 KT  75 MPH...INLAND
 36H  14/0000Z 27.1N 103.3W   30 KT  35 MPH...INLAND
 48H  14/1200Z 30.7N  99.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  15/0000Z...DISSIPATED INLAND

$$
Forecaster Stewart



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