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Tropical Storm Pamela Forecast Discussion Number 11
2021-10-12 23:09:44| National Hurricane Center (East Pacific)
Issued at 300 PM MDT Tue Oct 12 2021 390 WTPZ41 KNHC 122053 TCDEP1 Tropical Storm Pamela Discussion Number 11 NWS National Hurricane Center Miami FL EP162021 300 PM MDT Tue Oct 12 2021 Entrainment of very dry mid-level air from the west and northwest appears to have eroded Pamela's deep convection in the northwestern semicircle, leaving the low-level center partially exposed again similar to this time yesterday. Although there could still be some upper-level wind shear affecting the cyclone, dropsonde wind data from an earlier Air Force Reserve reconnaissance aircraft indicate that the vortex column from the surface to at least the 700-mb level was vertically aligned with no tilt evident. The highest aircraft flight-level and SFMR winds only support an intensity of about 55 kt. However, the aircraft measured a central pressure of 989 mb on its second and outbound pass through the center, which was a decrease of 2 mb from the first pass, and would support an intensity close to hurricane strength. Based on the relatively low central pressure, and the possibility that stronger winds might exist east of the center in an area that wasn't sampled by the aircraft, Pamela's intensity has only been lowered to 60 kt for this advisory. Data from the aircraft indicated that the 34-kt wind radii had expanded in all quadrants despite Pamela's peak winds having weakened. Another Air Force Reserve reconnaissance aircraft is scheduled to investigate Pamela later tonight around 0530 UTC. The initial motion estimate is northward, or 360/08 kt. Now that Pamela is on or just north of the axis of a deep-layer ridge, a sharp turn toward the north-northeast should occur very soon, followed by a northeastward motion tonight as the cyclone becomes embedded within southwesterly flow ahead of a broad mid- to upper-level trough. Pamela should then accelerate toward the west-central coast of Mexico tonight through Wednesday due to the deep-layer steering flow on the southeast side of the aforementioned trough. Landfall is still expected to occur along the west-central coast of Mexico a little before 1200 UTC Wednesday morning. After the hurricane moves inland, Pamela, or its remnants will continue to accelerate northeastward across central and northern Mexico, and move into Texas by Thursday night. The new NHC track model guidance remains tightly packed around the previous advisory track, so no significant changes were required. It might not seem like it based on the downward satellite trends today, but the negative effects from modest vertical shear and dry air that have been affecting the cyclone will gradually subside once Pamela makes the expected northeastward turn later this evening. During that same time, the deep-layer shear vector is forecast to slowly back around to a southwesterly direction and become aligned with the hurricane's forward motion, which will help to reduce some of the effects of the shear. Surrounding dry mid-level air could still be a hindering factor, but this negative parameter is expected to be offset by Pamela moving over very warm sea-surface temperatures of almost 31 deg C overnight. The higher ocean heat content should increase the available instability during the normal convective maximum period tonight, enabling the cyclone to restrengthen to hurricane status, and continue to strengthen right up until landfall occurs. Although it now appears unlikely that the cyclone will become a major hurricane, Pamela could still become a category 2 hurricane prior to landfall. After landfall occurs, rapid decay due to interaction with the mountainous terrain of Mexico is expected, with the cyclone ultimately dissipating over northern Mexico in a couple of days. The latest NHC intensity forecast lies near or above the upper end of the intensity guidance. 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 restrengthen into a hurricane before 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 this afternoon and tonight, and tropical-storm conditions are possible within the Tropical Storm Watch area, primarily in strong gusts. 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 the remnants of Pamela are expected across portions of central Texas and southeastern Oklahoma late Wednesday and Thursday. This may result in considerable flash and urban flooding impacts. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 21.0N 109.3W 60 KT 70 MPH 12H 13/0600Z 22.7N 107.9W 75 KT 85 MPH 24H 13/1800Z 25.4N 105.2W 35 KT 40 MPH...INLAND 36H 14/0600Z 28.8N 101.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 14/1800Z 32.0N 97.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 15/0600Z...DISSIPATED INLAND $$ Forecaster Stewart
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