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Tropical Storm Pamela Forecast Discussion Number 12

2021-10-13 04:37:55| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Tue Oct 12 2021 000 WTPZ41 KNHC 130237 TCDEP1 Tropical Storm Pamela Discussion Number 12 NWS National Hurricane Center Miami FL EP162021 900 PM MDT Tue Oct 12 2021 Westerly shear has continued to prevent Pamela from restrengthening this evening. Although there was a significant burst of deep convection since the previous advisory, the center remains on the northwestern edge of the convective cloud mass and more recently the cloud tops associated with that burst has begun to warm. A blend of subjective Dvorak T- and CI-numbers from SAB and TAFB, and the latest UW-CIMSS SATCON estimate stills support an initial intensity of 60 kt. Another Air Force Reserve reconnaissance aircraft is scheduled to investigate Pamela overnight, which should provide a better assessment of the cyclone's intensity. Recent center fixes show that Pamela has made its much anticipated north-northeastward turn, and it is now moving 020/10 kt. The tropical storm should accelerate northeastward during the next 12 to 24 hours as it gets caught in deep-layer southwesterly flow between a mid-level ridge over the western Gulf of Mexico, and an approaching mid-latitude trough to the northwest. This motion should bring the center of Pamela to the coast of west-central mainland Mexico around 1200 UTC Wednesday morning. After that time, Pamela or its remnants should continue moving quickly northeastward across central and northern Mexico through Wednesday night. Although a 36-h post-tropical cyclone point is shown over southern Texas, the low-level center is likely to dissipate over the mountainous terrain of Mexico late Wednesday or Wednesday night. Pamela will be moving over very warm SSTs of around 31C overnight, and that combined with a slightly more conducive upper-level wind pattern should allow Pamela to restrengthen into a hurricane before it reaches the coast of Mexico Wednesday morning. After landfall, rapid weakening will occur as Pamela moves over the rugged terrain of west-central Mexico. The latest NHC intensity forecast is again near the higher side of the guidance envelope, but it shows a slightly lower peak intensity before landfall than the previous official forecast. Although Pamela is likely 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. Heavy rains associated with Pamela are expected to move into the Mexican States of Sinaloa and western Durango along with southern portions of Baja California Sur tonight and Wednesday. This will pose a threat of significant and life-threatening flash flooding and mudslides. 3. 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 13/0300Z 21.9N 108.7W 60 KT 70 MPH 12H 13/1200Z 23.8N 106.9W 70 KT 80 MPH...NEAR THE COAST 24H 14/0000Z 26.6N 103.3W 30 KT 35 MPH...INLAND 36H 14/1200Z 29.7N 99.7W 20 KT 25 MPH...POST-TROP/INLAND 48H 15/0000Z...DISSIPATED $$ Forecaster Brown

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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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Hurricane Pamela Forecast Discussion Number 10

2021-10-12 16:42:49| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Tue Oct 12 2021 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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Hurricane Pamela Forecast Discussion Number 9

2021-10-12 10:34:36| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Tue Oct 12 2021 003 WTPZ41 KNHC 120834 TCDEP1 Hurricane Pamela Discussion Number 9 NWS National Hurricane Center Miami FL EP162021 300 AM MDT Tue Oct 12 2021 After being relatively steady in strength for the past 12 hours or so, satellite images indicate that Pamela has resumed intensifying. A large area of deep convection has developed during the past several hours, and the center is estimated to be located near the middle of the convective mass. The Dvorak classifications from TAFB and SAB have both increased to 4.0/65 kt, and therefore, Pamela has now been upgraded to a 65-kt hurricane. An Air Force Reserve reconnaissance aircraft is scheduled to fly into the storm later this morning and early afternoon to provide a better assessment of Pamela's structure, intensity, and wind field. Pamela has made the expected turn to the north, with the latest initial motion estimated to be 360/10 kt. The system is now on the western periphery of the ridge, which should cause it to continue moving northward today. However, by tonight, Pamela is forecast to become embedded in the flow on the south side of a broad mid- to upper-level trough, and that feature should cause the hurricane to move faster to the northeast toward the coast of west-central Mexico. After the storm moves inland early Wednesday, Pamela, or its remnants should accelerate northeastward across central and northern Mexico by the end of the week. The NHC track forecast is similar to the previous one and near the middle of the guidance envelope. Even though Pamela has not strengthened as quickly as thought up to this point, the overall intensity forecast philosophy has not changed much. The storm is expected to be in generally favorable conditions to gain strength until it reaches the coast of Mexico in 24 to 36 hours. Therefore, the NHC forecast continues to predict steady to rapid strengthening, and Pamela is likely to be near major hurricane intensity when it makes landfall. After landfall, Pamela is expected to rapidly decay due to the rugged terrain of Mexico, and it should ultimately dissipate over northern Mexico in 2 to 3 days. The NHC intensity forecast lies at the high end of the model guidance. Although the cyclone is forecast to dissipate over the mountainous 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 an 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 later today 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 flash and urban flooding. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 19.2N 108.9W 65 KT 75 MPH 12H 12/1800Z 20.5N 108.8W 75 KT 85 MPH 24H 13/0600Z 22.4N 107.6W 90 KT 105 MPH 36H 13/1800Z 25.1N 105.1W 50 KT 60 MPH...INLAND 48H 14/0600Z 28.4N 101.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 14/1800Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Storm Pamela Forecast Discussion Number 8

2021-10-12 04:38:03| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Mon Oct 11 2021 000 WTPZ41 KNHC 120237 TCDEP1 Tropical Storm Pamela Discussion Number 8 NWS National Hurricane Center Miami FL EP162021 900 PM MDT Mon Oct 11 2021 Pamela continues to be affected by some modest northwesterly mid-level shear that has caused the low-level center to be located near the northwestern edge of the deep convection. This was evident in an earlier AMSR2 microwave image that arrived shortly after the release of the previous NHC advisory package. Recent objective and subjective Dvorak T-numbers still support an intensity of around 60 kt, and that value is maintained as the initial wind speed for this advisory. An Air Force Reserve reconnaissance aircraft is scheduled to fly into the storm late tomorrow morning and early afternoon to better provide a better assessment of Pamela's structure, intensity, and wind field. The guidance suggests that the shear that has been plaguing Pamela should relax during the next 12-24 hours, allowing for strengthening. Nearly all of the statistical and dynamical model intensity guidance calls for strengthening, but they have trended toward a lower peak intensity primarily due to the fact that Pamela so far has not strengthened as much as expected. The NHC intensity forecast again calls for Pamela to become a hurricane overnight or early Tuesday, and shows the system nearing major hurricane strength before it reaches the coast of mainland Mexico early Wednesday. Although the official forecast is at the high end of the intensity guidance, it is supported by the GFS model which has been consistent in significantly deepening Pamela during the cyclone's approach to Mexico on Tuesday and Tuesday night. After landfall, rapid weakening should occur as the system moves over the mountainous terrain of west-central Mexico, and Pamela is forecast to become a post-tropical remnant low or dissipate by Thursday. Pamela is moving north-northwestward or 335/7 kt. The track forecast philosophy again remains unchanged this advisory. The cyclone is forecast to turn northward tonight as it reaches the western portion of a deep-layer subtropical ridge. A faster northeastward motion is expected by late Tuesday as Pamela recurves ahead of a broad mid-latitude trough moving into northwestern Mexico. The track guidance is in very good agreement on the overall evolution of the steering pattern, but there are still some differences in how quickly Pamela accelerates northeastward on Tuesday. Therefore, the NHC forecast is once again close to the various multi-model consensus aids. Although the cyclone could dissipate over the mountainous 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 southwestern 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 on Tuesday and Tuesday night, 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 the remnants of 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 12/0300Z 17.9N 108.9W 60 KT 70 MPH 12H 12/1200Z 19.2N 109.1W 70 KT 80 MPH 24H 13/0000Z 21.0N 108.5W 85 KT 100 MPH 36H 13/1200Z 23.1N 106.9W 95 KT 110 MPH 48H 14/0000Z 26.1N 103.3W 40 KT 45 MPH...INLAND 60H 14/1200Z 29.5N 99.5W 25 KT 30 MPH...POST-TROP/INLAND 72H 15/0000Z...DISSIPATED $$ Forecaster Brown

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