Tropical Storm Willa

Tropical Depression Willa Track 0400 Hours October 24 2018
Tropical Depression Willa Track 0400 Hours October 24 2018

NWS National Hurricane Center Miami FL 1000 AM CDT Wed Oct 24 2018

Tropical Storm Willa (see 17 videos below) – Satellite images and surface observations indicate that Willa’s surface circulation has dissipated over northeastern Mexico, so this is the final advisory.

It should be noted that a non-tropical cyclone that is forecast to move from the Gulf of Mexico to the northeastern United States over the next few days is a separate system, and not directly associated with Willa’s remnants.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 25.5N 101.5W   20 KT  25 MPH - Tropical Depression (Gral Cepeda, Mexico)
 12H  25/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 400 AM CDT Wed Oct 24 2018

Tropical Depression Willa Satellite images and surface observations indicate that Willa is located well inland over the eastern portion of the Mexican state of Durango. Deep-layer southwesterly flow ahead of a mid-latitude trough will continue to drive the mid and upper-level circulations to the northeast and farther inland, with the low-level circulation shearing away and lagging back to the southwest due to the blocking high terrain of west-central and northern Mexico. A 12-hour forecast position has been provided for continuity purposes, which reflects where the mid-level circulation center is expected to be since the cyclone will likely have dissipated by then.

Although Willa has weakened to a tropical depression, wind speeds atop and on the windward sides of hills and mountains are often up to 30 percent stronger than the near-surface winds indicated in this advisory. Therefore, strong tropical-storm-force winds gusts will still be possible this morning, especially in stronger thunderstorms occurring to the east and south of the center.

Key Messages:

1. Storm surge will subside this morning along the coasts of southern Sinaloa and Nayarit states in west-central and southwestern Mexico.

2. Heavy rainfall from Willa is likely to produce life-threatening flash flooding and landslides over much of southwestern and west-central Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  24/0900Z 24.4N 103.6W   30 KT  35 MPH - Tropical Stom (Cuencamé, Mexico)
 12H  24/1800Z 26.0N 100.5W   20 KT  25 MPH - Post Tropical (Mina - Hidalgo, Mexico)
 24H  25/0600Z...DISSIPATED INLAND

NWS National Hurricane Center Miami FL 1000 PM CDT Tue Oct 23 2018

Hurricane Willa  – Satellite images indicate that at 0100 UTC, the eye of Willa crossed the coast of Mexico near Isla del Bosque, Sinaloa about 50 miles (80 km) southeast of Mazatlan. Willa made landfall as a Category 3 hurricane with estimated sustained winds of 105 kt. The hurricane is already inland and still has an eye feature surrounded by a ring of very deep convection. However, the eye is beginning to gradually fade on satellite. The winds are probably already lower, and the initial intensity is set at 100 kt. Willa is forecast to move farther inland over the high mountains of western Mexico resulting in rapid weakening. It is anticipated that by tomorrow, the cyclone will no longer have a low-level circulation and dissipate.

Satellite fixes indicate that the eye has been moving toward the northeast a little faster, about 15 kt. The hurricane is well embedded within the mid-latitude westerlies, and this flow pattern should steer the cyclone on this general track with an increase in forward speed until dissipation over western Mexico tomorrow.

Key Messages:

1. Life-threatening storm surge is still occurring along the coasts of southern Sinaloa and Nayarit states in west-central and southwestern Mexico near the path of Willa.

2. Damaging and life-threatening hurricane-force winds should continue within the hurricane warning area during the next several hours and continue to spread inland across the mountainous areas of west-central Mexico.

3. Heavy rainfall from Willa is likely to produce life-threatening flash flooding and landslides over much of southwestern and west-central Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  24/0300Z 23.2N 105.5W  100 KT 115 MPH - Category 3 (Pueblo Nuevo, Mexico)
 12H  24/1200Z 25.0N 103.0W   30 KT  35 MPH - Tropical Storm (Viesca, Mexico)
 24H  25/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 PM MDT Tue Oct 23 2018

Hurricane Willa’s earlier eyewall replacement cycle appears to have finally ended with the erosion of the small inner eye and the outer eye becoming better defined in microwave data. The eye has also warmed and become more evident in infrared and visible satellite imagery this afternoon. The Air Force Reserve reconnaissance aircraft that flew into Willa earlier today measured a peak 700-mb flight-level wind of 109 kt in the southeast quadrant and SFMR winds of around 100 kt. Since the aircraft was only able to perform a single pass through each quadrant, there is likely some undersampling so the initial wind speed is set at 105 kt.

Satellite and the earlier aircraft fixes show that Willa is moving a little faster toward the north-northeast, or around 030/9 kt. The hurricane is expected to accelerate northeastward ahead of a shortwave trough that is passing near the Baja California peninsula. The dynamical model guidance is in good agreement in showing that the center of Willa will reach the coast of west-central Mexico very soon, and then track inland over central Mexico tonight and Wednesday. The track guidance envelope has not changed much this cycle, and no significant changes were needed to the previous official track.

Although the satellite presentation of Willa has improved somewhat this afternoon, little change in strength is expected before the hurricane reaches the coast of Mexico. Increasing southwesterly shear and the mountainous terrain of mainland Mexico will cause Willa to rapidly weaken after it moves inland tonight and Wednesday. A 24-h forecast point is provided for continuity, but it is unlikely that the low-level circulation will survive its passage over the mountainous terrain for that long of a time period.

Key Messages:

1. Life-threatening storm surge is occurring along the coasts of the Isla Marias, and along the coast of southern Sinaloa and Nayarit states in west-central and southwestern Mexico near the path of Willa.

2. Damaging and life-threatening hurricane-force winds will reach the coast of west-central Mexico within the hurricane warning area within the next few hours. Hurricane-force winds will also extend inland across the mountainous areas of west-central Mexico as Willa moves inland.

3. Heavy rainfall from Willa is likely to produce life-threatening flash flooding and landslides over much of southwestern and west-central Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 22.2N 106.4W  105 KT 120 MPH - Category 3 (WSW Playa Novillero, Mexico)
 12H  24/0600Z 23.7N 104.7W   50 KT  60 MPH - Tropical Storm (Durango, Mexico)
 24H  24/1800Z 25.7N 101.3W   25 KT  30 MPH - Post Tropical (Ramos Arizpe, Mexico)
 36H  25/0600Z...DISSIPATED

NWS National Hurricane Center Miami FL 900 AM MDT Tue Oct 23 2018

Hurricane Willa’s overall satellite presentation has not changed much during the past few hours, with some evidence of a small inner core and and an outer eyewall. Recent microwave data and reports from an Air Force Reserve Hurricane Hunter aircraft also indicate that concentric eyewalls are present. The reconnaissance aircraft just completed its first pass into the center and found peak 700-mb flight-level winds of 107 kt, and SFMR winds of 99 kt. The plane reported a minimum pressure of 966 mb, which was higher than previously estimated. Based on the preliminary aircraft data and a blend of Dvorak T- and CI-numbers from the various agencies, the initial intensity is set at 110 kt. The plane should provide a more accurate assessment of Willa’s intensity as it continues its mission during the new few hours.

Willa is moving a little east of due north or 010/5 kt. A shortwave trough approaching the west coast of the Baja California peninsula is expected to cause Willa to turn north-northeastward this morning, and the hurricane should accelerate northeastward by tonight. The core of Willa will move over the Isla Marias within the next few hours, and make landfall along the west-central coast of Mexico this evening. The track guidance is in good agreement, and the updated NHC track forecast is very similar to the previous advisory.

Although Willa is moving over an area of deep warm water, increasing southwesterly shear is likely to cause gradual weakening as the hurricane approaches the coast. Despite the forecast decrease in the peak winds, Willa is expected to remain a dangerous hurricane through landfall, bringing life-threatening storm surge, wind, and rainfall hazards to Las Islas Marias and portions of west-central and southwestern Mexico. After landfall, Willa will rapidly weaken over the mountains of mainland Mexico, and dissipation is expected on Wednesday. Moisture from the remnants of this system is forecast to spread northeastward over northern Mexico and portions of Texas and the northern Gulf Coast where a swath of heavy rainfall is expected.

Key Messages:

1. A life-threatening storm surge is expected along the coasts of the Isla Marias, and along the coast of southern Sinaloa and Nayarit states in west-central and southwestern Mexico near the path of Willa.

2. Damaging and life-threatening hurricane-force winds are expected over the Isla Marias, and within the hurricane warning area along the coast of west- central Mexico. Hurricane-force winds will also extend inland across the mountainous areas of west-central Mexico as Willa moves inland.

3. Heavy rainfall from Willa is likely to produce life-threatening flash flooding and landslides over much of southwestern and west-central Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 21.4N 106.9W  110 KT 125 MPH - Category 3 (WSW Isla Maria Magdalena, Mexico)
 12H  24/0000Z 22.7N 105.9W   95 KT 110 MPH - Category 2 (WSW Isla del Bosque, Mexico)
 24H  24/1200Z 24.9N 102.9W   35 KT  40 MPH - Tropical Storm (Viesca, Mexico)
 36H  25/0000Z 26.7N  99.8W   20 KT  25 MPH - Post Tropical (Vallecillo, Mexico)
 48H  25/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 600 AM MDT Tue Oct 23 2018

DISCUSSION AND OUTLOOK

At 600 AM MDT (1200 UTC), the center of Hurricane Willa Hurricane Willa’s was located near latitude 21.1 North, longitude 107.1 West. Willa is moving toward the north near 5 mph (7 km/h). A turn toward the north- northeast is expected later this morning, followed by a faster motion toward the northeast by this evening. On the forecast track, the center of Willa will move near or over Las Islas Marias later this morning and afternoon, and make landfall within the hurricane warning area along the west-central coast of mainland Mexico late this afternoon or this evening.

Maximum sustained winds are near 130 mph (215 km/h) with higher gusts. Willa is an extremely dangerous category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. While gradual weakening is forecast today, Willa is expected to be a dangerous major hurricane when it reaches the coast of Mexico. Rapid weakening is expected after landfall tonight and continuing into Wednesday.

Hurricane-force winds extend outward up to 35 miles (55 km) from the center and tropical-storm-force winds extend outward up to 125 miles (205 km).

The estimated minimum central pressure is 945 mb (27.91 inches).

HAZARDS AFFECTING LAND

STORM SURGE: An extremely dangerous storm surge is likely along portions of the coast of southwestern Mexico in southern Sinaloa and Nayarit, especially near and to the south of where the center of Willa makes landfall. Near the coast, the surge will be accompanied by large and destructive waves.

RAINFALL: Willa is expected to produce storm total rainfall accumulations of 6 to 12 inches, with local amounts to 18 inches, across portions of western Jalisco, western Nayarit, southern Sinaloa, and far southern Durango in Mexico. This rainfall will cause life-threatening flash flooding and landslides.

Farther inland, Willa is expected to produce rainfall amount of 2 to 4 inches across the rest of Durango and portions of Zacateca, southeast Chihuahua, and Coahuila, with local amounts to 6 inches possible. This rainfall could cause life-threatening flash flooding.

WIND: Hurricane conditions are expected on Las Islas Maria today, and within the hurricane warning area along the coast of mainland Mexico beginning this afternoon. Tropical storm conditions are occurring on Las Islas Marias, and tropical storm conditions will spread northward along the coast of mainland Mexico within the warning area today.

SURF: Large swells generated by Willa will continue to affect portions of the coast of southwestern and west-central mainland Mexico, and the coast of the southern Baja California peninsula Swells during the next day or two. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

NWS National Hurricane Center Miami FL 300 AM MDT Tue Oct 23 2018

Hurricane Willa’s overall satellite presentation has continued to slowly degrade since the previous advisory, with the exception of a few brief attempts at redevelopment of an inner-core ring of deep convection. However, dry intrusions from the moat region between the larger outer eyewall and the smaller inner core have thus far prevented the reformation of an inner eyewall. Satellite intensity estimates have been steadily decreasing, and the advisory intensity is set at 115 kt, based on a average of the subjective T- and CI-numbers from TAFB and a UW-CIMSS ADT objective estimate of T6.0/115 kt. An Air Force Reserve Unit reconnaissance aircraft is scheduled to reconnoiter Hurricane Willa later this morning, providing more detailed intensity information.

The initial motion estimate remains northward, but at a slower forward speed, or 360/04 kt. There are no significant changes to the previous track forecast or reasoning. Willa is expected to move slowly northward this morning around the western periphery of a deep-layer ridge located over central Mexico, and then recurve toward the north-northeast and northeast at a faster forward speed by this afternoon ahead of an approaching mid-latitude trough, with that motion continuing into this evening and Wednesday. The new NHC track forecast is near the eastern edge of the tightly packed guidance envelope, near the FSSE and GFS model tracks.

There has been no microwave imagery since around 0100Z to provide information on the eyewall replacement cycle (ERC). However, conventional infrared satellite imagery suggests that the ERC is still ongoing based on the appearance of a partial moat or clear region in the northern semicircle of the inner core. Willa is currently moving over warmer and deeper water as indicated by upper-ocean heat content (UOHC) values greater than 50 units. This favorable ocean condition is expected to continue along the forecast track for another 12 hours or so, which could help to offset the weakening rate due to the gradual increase in the southwesterly wind shear. By 18 h, or just before landfall, the shear is forecast to increase to more than 20 kt and the warm water beneath the hurricane is expected to become more shallow, a combination that could lead to significant upwelling and weakening. However, the official intensity forecast follows the consensus of the various intensity models, keeping Willa’s intensity near 100 kt at landfall, which is similar to the FSSE and HCCA corrected-consensus models. Despite the forecast decrease in the peak winds, Willa is expected to remain a dangerous major hurricane through landfall, bringing life-threatening storm surge, wind, and rainfall hazards to Las Islas Marias and portions of west-central and southwestern Mexico later today. After moving inland, Willa will rapidly weaken, with dissipation forecast by Wednesday over the high terrain of Mexico. However, deep moisture from the remnants of Willa is forecast to spread northeastward over northern Mexico and portions of Texas where a swath of heavy rainfall is expected midweek.

Key Messages:

1. A life-threatening storm surge is expected today along the coasts of the Isla Marias, and along the coast of southern Sinaloa and Nayarit states in west-central and southwestern Mexico near the path of Willa. Residents should rush preparations to completion to protect life and property and follow any advice given by local officials.

2. Everyone in the Isla Marias, and within the hurricane warning area along the coast of west-central Mexico should prepare for life- threatening major hurricane winds associated with the core of Willa. Hurricane force winds will also extend inland across the mountainous areas of west-central Mexico as Willa moves inland.

3. Heavy rainfall from Willa is likely to produce life-threatening flash flooding and landslides over much of southwestern and west-central Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 20.8N 107.3W  115 KT 130 MPH - Category 4 (WNW Puerto Vallarta, Mexico)
 12H  23/1800Z 22.0N 106.5W  100 KT 115 MPH - Category 3 (WSW Puerta de Palapares, Mexico)
 24H  24/0600Z 23.8N 104.5W   40 KT  45 MPH - Tropical Storm (Durango, Mexico)
 36H  24/1800Z 25.8N 102.3W   20 KT  25 MPH - Post Tropical (San Pedro, Mexico)
 48H  25/0600Z...DISSIPATED INLAND

NWS National Hurricane Center Miami FL 600 PM MDT Mon Oct 22 2018

DISCUSSION AND OUTLOOK

Hurricane Willa  – At 600 PM MDT (0000 UTC), the center of Hurricane Willa was located near latitude 20.2 North, longitude 107.2 West. Willa is moving toward the north near 8 mph (13 km/h), and this general motion is expected to continue through tonight. Willa is forecast to accelerate toward the north-northeast and move over or very near the Islas Marias early Tuesday and then make landfall along the west- central coast of mainland Mexico in the hurricane warning area Tuesday afternoon or evening.

Maximum sustained winds are near 150 mph (240 km/h) with higher gusts. Willa is an extremely dangerous category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Gradual weakening is forecast during the next day or so, but Willa is expected to be a dangerous major hurricane when it reaches the coast of Mexico. Rapid weakening is expected after landfall Tuesday night and Wednesday.

Hurricane-force winds extend outward up to 35 miles (55 km) from the center and tropical-storm-force winds extend outward up to 125 miles (205 km).

The estimated minimum central pressure is 933 mb (27.55 inches).

HAZARDS AFFECTING LAND

STORM SURGE: An extremely dangerous storm surge is likely along portions of the coast of southwestern Mexico in southern Sinaloa and Nayarit, especially near and to the south of where the center of Willa makes landfall. Near the coast, the surge will be accompanied by large and destructive waves.

RAINFALL: Willa is expected to produce storm total rainfall accumulations of 6 to 12 inches, with local amounts to 18 inches, across portions of western Jalisco, western Nayarit, and southern Sinaloa in Mexico. This rainfall will cause life-threatening flash flooding and landslides.

Farther inland, Willa is expected to produce rainfall amount of 2 to 4 inches across portions of Zacateca, Durango, southeast Chihuahua, and Coahuila in Mexico, with local amounts to 6 inches possible. This rainfall could cause life-threatening flash flooding.

WIND: Hurricane conditions are expected within the hurricane warning area beginning Tuesday afternoon, with tropical storm conditions expected by early Tuesday. Tropical storm conditions are expected within the tropical storm warning areas tonight and Tuesday.

SURF: Large swells generated by Willa will continue to affect portions of the coast of southwestern and west-central Mexico during the next few days. Swells should begin to affect portions of the coast of the southern Baja California peninsula later today. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

NWS National Hurricane Center Miami FL 300 PM MDT Mon Oct 22 2018

Hurricane Willa continues to exhibit an impressive presentation in satellite imagery, however the small eye has become cloud filled this afternoon and and earlier microwave data indicated that an eyewall replacement cycle had begun. Subjective and objective data T-numbers are a little lower than this morning, and the initial intensity has been set at 135 kt for this advisory. The Air Force Reserve Hurricane Hunter aircraft that was en route to Willa around midday was struck by lightning in one of the outer rain bands and had to return to base due to safety issues regarding some of the onboard equipment.

The hurricane has been moving due northward today at about 7 kt. The track forecast reasoning remains unchanged from the previous advisory as Willa is currently moving around the western portion of a deep-layer ridge. An approaching shortwave trough should turn Willa north-northeastward, then northward toward the west-central coast of Mexico on Tuesday, and the hurricane is forecast to make landfall within the hurricane warning area between San Blas and Mazatlan Tuesday afternoon or evening. There are still some model differences regarding the timing of landfall, and the NHC track forecast is near the various consensus aids to account for these variations in forward speed.

The rapid intensification phase that Willa has gone through since its formation on Saturday appears to have ended now that an eyewall replacement has begun. Although the hurricane is forecast to remain in a low to moderate wind shear environment and over warm SSTs through tonight, some weakening is likely due to internal dynamics of the eyewall replacement. Increasing southwesterly shear on Tuesday is likely to cause some additional weakening, and the NHC intensity forecast has been adjusted accordingly, however, Willa is forecast to remain a dangerous major hurricane through landfall. Rapid weakening will occur Tuesday night as Willa moves over the mountainous terrain of Mexico, and the cyclone is expected to dissipate on Wednesday. Moisture from the remnants of Willa are forecast to spread northeastward over northern Mexico and portions of Texas where a swath of heavy rainfall is expected midweek.

Key Messages:

1. A life-threatening storm surge is expected Tuesday along the coasts of the Isla Marias, and west-central and southwestern Mexico near the path of Willa. Residents should rush preparations to completion to protect life and property and follow any advice given by local officials.

2. Everyone in Isla Marias, and within the hurricane warning area along the coast of west-central Mexico should prepare for life- threatening major hurricane winds associated with the core of Willa. Hurricane force winds will also extend inland across the mountainous areas of west-central Mexico as Willa moves inland.

3. Heavy rainfall from Willa is likely to produce life-threatening flash flooding and landslides over much of southwestern and west-central Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 19.7N 107.2W  135 KT 155 MPH - Category 4 (WSW Tomatlán, Mexico)
 12H  23/0600Z 20.7N 107.1W  125 KT 145 MPH - Category 4 (WSW Puerto Vallarta, Mexico)
 24H  23/1800Z 22.0N 106.5W  110 KT 125 MPH - Category 3 (WSW Puerta de Palapares, Mexico)
 36H  24/0600Z 23.9N 104.7W   60 KT  70 MPH - Tropical Storm (Durango, Mexico)
 48H  24/1800Z 26.2N 101.5W   25 KT  30 MPH - Post Tropical (Ramos Arizpe, Mexico)
 72H  25/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1200 PM MDT Mon Oct 22 2018

DISCUSSION AND OUTLOOK

At 1200 PM MDT (1800 UTC), the center of Hurricane Willa  was located near latitude 19.4 North, longitude 107.2 West. Willa is moving toward the north near 7 mph (11 km/h), and this general motion is expected to continue today. Willa is forecast to accelerate toward the north-northeast and move over or very near the Islas Marias early Tuesday and make landfall along the southwestern coast of mainland Mexico in the hurricane warning area Tuesday afternoon or evening.

Maximum sustained winds are near 160 mph (260 km/h) with higher gusts. Willa is a category 5 hurricane on the Saffir-Simpson Hurricane Wind Scale. Some strengthening is still possible today. Slight weakening is forecast to begin on Tuesday, but Willa is expected to be an extremely dangerous major hurricane when it reaches the coast of Mexico.

The Air Force Reserve Hurricane Hunter Aircraft that was en route to Willa experienced a safety issue before entering the storm and had to return to base.

Hurricane-force winds extend outward up to 30 miles (45 km) from the center and tropical-storm-force winds extend outward up to 105 miles (165 km).

The estimated minimum central pressure is 925 mb (27.32 inches).

HAZARDS AFFECTING LAND

STORM SURGE: An extremely dangerous storm surge is likely along portions of the coast of southwestern Mexico by Tuesday or Tuesday night, especially near and to the south of where the center of Willa makes landfall. Near the coast, the surge will be accompanied by large and destructive waves.

RAINFALL: Willa is expected to produce storm total rainfall accumulations of 6 to 12 inches, with local amounts to 18 inches, across portions of western Jalisco, western Nayarit, and southern Sinaloa in Mexico. This rainfall will cause life-threatening flash flooding and landslides.

Farther inland, Willa is expected to produce rainfall amount of 2 to 4 inches across portions of Zacateca, Durango, southeast Chihuahua, and Coahuila in Mexico, with local amounts to 6 inches possible. This rainfall could cause life-threatening flash flooding.

WIND: Hurricane conditions are expected within the hurricane warning area beginning Tuesday afternoon, with tropical storm conditions expected by Tuesday morning. Tropical storm conditions are expected within the tropical storm warning areas by tonight and Tuesday.

SURF: Large swells generated by Willa will continue to affect portions of the coast of southwestern and west-central Mexico during the next few days. Swells should begin to affect portions of the coast of the southern Baja California peninsula later today. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

NWS National Hurricane Center Miami FL 900 AM MDT Mon Oct 22 2018

Hurricane Willa is an extremely impressive hurricane in infrared and visible satellite imagery this morning. The small, but very distinct, eye is embedded within a symmetric central dense overcast with cloud tops of -70 to -80 degrees Celsius. A very recent SSMIS microwave overpass is the first to indicate that an outer eyewall has formed, suggesting that an eyewall replacement cycle has started. The latest objective T-numbers from UW-CIMSS are T7.0/140 kt, and subjective Dvorak intensity estimates from TAFB and SAB are 140 kt and 127 kt, respectively. Based on these data the initial intensity has been increased to 140 kt. An Air Force Reserve Hurricane Hunter aircraft is currently en route to Wilma and should provide a better assessment of the storm’s intensity by early this afternoon.

Willa is moving northward 6 kt. The hurricane is forecast to continue to move northward today around the western flank of a deep-layer ridge that is located over the Gulf of Mexico. A short wave trough that is seen in water vapor imagery near 130W longitude is forecast to deepen as it moves eastward toward Baja California. This should cause Willa to turn north-northeastward tonight, then accelerate northeastward on Tuesday, bringing the center of the hurricane onshore along the west-central coast of Mexico Tuesday afternoon or evening. As mentioned in the previous advisory, the track guidance is good agreement on the overall scenario but there are still some notable differences in the predicted forward speed of the hurricane. The NHC track forecast leans toward the faster solutions of the GFS and GFS ensemble mean, which have been handling Willa’s track the best so far.

The environment of low wind shear and water temperatures of 28 to 29.5 degrees Celsius suggest some additional strengthening is possible but with the evidence that an eyewall replacement has begun, some fluctuations intensity are possible during the next 12 to 24 hours. After that time, increasing southwesterly shear is forecast to induce weakening, but Willa is likely to remain an extremely dangerous major hurricane when it makes landfall along the west-central coast of Mexico. After landfall, shear and the mountainous terrain of Mexico will cause rapid weakening and dissipation of the cyclone.

Key Messages:

1. A life-threatening storm surge is expected Tuesday along the coasts of the Isla Marias, and west-central and southwestern Mexico near the path of Willa. Residents should rush preparations to completion to protect life and property and follow any advice given by local officials.

2. Everyone in Isla Marias, and within the hurricane warning area along coast of west-central Mexico should prepare for life- threatening major hurricane winds associated with the core of Michael. Hurricane force winds will also extend inland across the mountainous areas of west-central Mexico as Willa moves inland.

3. Heavy rainfall from Willa is likely to produce life-threatening flash flooding and landslides over much of southwestern and west-central Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  22/1500Z 19.1N 107.2W  140 KT 160 MPH - Category 5 (WSW La Manzanilla, Mexico)
 12H  23/0000Z 20.1N 107.2W  140 KT 160 MPH - Category 5 (WSW Tehualmixtle, Mexico)
 24H  23/1200Z 21.4N 106.9W  135 KT 155 MPH - Category 4 (W Isla Maria Magdalena, Mexico)
 36H  24/0000Z 23.1N 105.6W   90 KT 105 MPH - Category 2 (Rosario, Mexico)
 48H  24/1200Z 25.4N 102.5W   30 KT  35 MPH - Tropical Storm (Parras, Mexico)
 72H  25/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 AM MDT Mon Oct 22 2018

Hurricane Willa is an impressive hurricane with rapid to explosive deepening having occurred over the past 48 hours, and yielding a 105-kt intensity increase during that time. Satellite intensity estimates range from subjective Dvorak T-numbers of T6.5/127 kt from TAFB and SAB to objective T-numbers of T7.0/140 kt from UW-CIMSS ADT and NHC. The most recent UW-CIMSS SATCON value around 0437Z was 127 kt. Based on these data and the slightly more ragged appearance of the CDO over the past couple of hours, the intensity is raised to 135 kt, which is just below category 5 strength. Willa is now moving northward and the initial motion estimate is 360/06 kt.

Willa is forecast to continue moving northward today as the hurricane rounds the western portion of a deep-layer ridge located over central Mexico and which extends westward along 20N latitude to near the Pacific coast of Mexico. On Tuesday, a turn toward the north-northeast and northeast at a slightly faster forward speed is expected as the hurricane gets caught up in southwesterly flow ahead of an approaching mid-/upper-level trough. The latest 00Z NHC model guidance is in decent agreement on this general track scenario, but with noticeable differences in the forward speed. Internal statistical analyses show that the ECMWF and UKMET models have had a slow westward bias over the past 48 hours, which has significantly affected the consensus models. As a result, the new NHC forecast is a little to the right of and slightly faster the previous advisory track and the consensus models, and lies close to GFS model which has verified the best thus far. On the forecast track, Willa is expected to move over Las Islas Marias on Tuesday and then move inland over southwestern and west-central Mexico Tuesday night or early Wednesday. A 72-hour position has been provided only for continuity purposes beyond the 48-hour period, and Willa will likely have dissipated by then.

Water temperatures ahead of the powerful hurricane are forecast to increase from 28 deg C to near 29.5 deg C, and the depth of the warm water is also expected to increase, which would tend to offset any cold upwelling beneath Willa. The deep-layer shear is forecast to increase to a little more than 10 kt during the next 36 hours, and remain at that level during the duration of that time period. These conditions would favor at least slight strengthening before the internal dynamics of the hurricane in the form of an eyewall replacement cycle (ERC) induces some weakening. With the eye diameter already at 10-15 nmi, an ERC could begin at any time during the next 12 hours. Shortly after 36 hours, the shear is expected to increase sharply to more than 20 kt, which will cause more significant weakening. However, Willa is still expected to be near major hurricane strength when it makes landfall along the west-central coast of Mexico. After landfall, the mountainous terrain along with strong southwesterly wind shear of more than 30 kt will cause rapid weakening and dissipation of the cyclone inland over north-central Mexico.

Key Messages:

1. Willa is forecast to be a dangerous hurricane when it reaches the Islas Marias and the coast of southwestern Mexico by late Tuesday or Wednesday morning, bringing a life-threatening storm surge and flash flooding along with damaging hurricane-force winds. A Hurricane Warning is in effect for these areas, and residents should rush preparations to completion to protect life and property and follow any advice given by local officials.

FORECAST POSITIONS AND MAX WINDS

INIT  22/0900Z 18.2N 107.1W  135 KT 155 MPH - Category 4 (WSW Manzanillo, Mexico)
 12H  22/1800Z 19.2N 107.2W  135 KT 155 MPH - Category 4 (WSW Tomatlán, Mexico)
 24H  23/0600Z 20.4N 107.2W  125 KT 145 MPH - Category 4 (WSW Puerto Vallarta, Mexixo)
 36H  23/1800Z 21.8N 106.5W  115 KT 130 MPH - Category 4 (ENE Isla San Juanico, Mexico)
 48H  24/0600Z 23.8N 104.6W   50 KT  60 MPH - Tropical Storm (Durango, Mexico)
 72H  25/0600Z 27.0N  99.5W   20 KT  25 MPH - Post Tropical (Guerrero, Mexico)
 96H  26/0600Z...DISSIPATED INLAND

NWS National Hurricane Center Miami FL 900 PM MDT Sun Oct 21 2018

Hurricane Willa has continued to rapidly intensify this evening. Satellite images show a well-defined circular eye with a surrounding ring of cold cloud tops that are near -80 deg C over the southeastern quadrant. The initial intensity is set to 125 kt, which is near the latest Dvorak ADT estimates from CIMSS at the University of Wisconsin. Willa has strengthened at an incredible rate since genesis, intensifying from a tropical depression to a category 4 hurricane in less than 48 hours.

Willa is gradually turning toward the right, with the initial motion estimated to be 340/6 kt. The hurricane is expected to turn northward on Monday as it moves around the western periphery of a mid-level ridge to the east, followed by a faster northeastward motion Monday night and Tuesday when a shortwave trough approaches the system. The models are in fairly good agreement, and only small changes were made to the previous NHC track forecast. On the forecast track, Willa is expected to move over Las Islas Marias on Tuesday and then move inland over southwestern and west-central Mexico Tuesday night or early Wednesday.

The hurricane has certainty taken advantage of the near ideal environmental conditions and since these conditions will persist a little longer, some additional strengthening is shown in the short term. However, some fluctuations in intensity could occur due to eyewall replacement cycles. The models then show a gradual increase in shear and a decrease in available moisture around 24 hours, and these factors should cause a slow weakening trend. Regardless, Willa is forecast to remain a dangerous hurricane, bringing multiple life-threatening hazards to the coast of Mexico. Rapid weakening is forecast after the system moves inland and interacts with the mountainous terrain. The NHC intensity forecast lies near the high end of the model guidance through dissipation.

Key Messages:

1. Willa is forecast to be a dangerous hurricane when it reaches the Islas Marias and the coast of southwestern Mexico by late Tuesday or Wednesday bringing a life-threatening storm surge and flash flooding along with damaging hurricane-force winds. A Hurricane Warning is in effect for these areas, and residents should rush preparations to completion to protect life and property and follow any advice given by local officials.

FORECAST POSITIONS AND MAX WINDS

INIT  22/0300Z 17.7N 107.2W  125 KT 145 MPH - Category 4 (WNW Lázaro Cárdenas, Mexico)
 12H  22/1200Z 18.6N 107.4W  135 KT 155 MPH - Category 4 (WSW Manzanillo, Mexico)
 24H  23/0000Z 19.7N 107.5W  125 KT 145 MPH - Category 4 (WNW Puerto Vallarta, Mexico)
 36H  23/1200Z 20.7N 107.2W  115 KT 130 MPH - Category 4 (WNW Puerto Vallarta, Mexico)
 48H  24/0000Z 22.1N 106.2W  100 KT 115 MPH - Category 3 (W Puerta de Palapares, Mexico)
 72H  25/0000Z 26.2N 101.3W   30 KT  35 MPH - Tropical Storm (Ramos Arizpe, Mexico)

NWS National Hurricane Center Miami FL 300 PM MDT Sun Oct 21 2018

Hurricane Willa  has continued to rapidly strengthen with the eye becoming very distinct in both visible and infrared satellite imagery. The surrounding convective tops warmed around mid-day but have cooled since that time and subjective Dvorak intensity estimates were 102 and 90 kt, from SAB and TAFB respectively at 18Z. With the continued increase in organization since that time, the initial intensity is set near the upper end of the estimates or 100 kt.

Willa continues moving slowly north-northwestward or 330/5 kt. There has been no change to the track forecast philosophy over the past few advisories. The hurricane is expected to turn northward tonight or Monday around the western portion of a deep-layer ridge that extends westward from the Gulf of Mexico over mainland Mexico. A mid-level trough that is forecast to approach the Baja California peninsula Monday night and Tuesday should cause Willa to turn north- northeastward and recurve around the northwestern portion of the aforementioned ridge. There are still some differences in how quickly Willa will recurve, but there is little cross-track spread in the guidance. This increases the overall confidence in the NHC track forecast, which calls for the hurricane to make landfall along the southwestern coast of Mexico late Tuesday or early Wednesday.

The low shear and warm ocean environment ahead of Willa is expected to remain quite favorable for strengthening for at least another 12 to 24 hours, and additional intensification is likely tonight and early Monday. The new NHC track intensity forecast is above all the intensity guidance through 36 hours, and now calls for a peak intensity of 130 kt within that time period. After that time, eyewall replacement cycles could result in some fluctuations in intensity. Increasing southwesterly shear on Tuesday could result in some weakening, but Willa is expected to approach the coast of Mexico as a very dangerous hurricane. After landfall, rapid weakening and dissipation over the mountainous terrain of mainland Mexico should occur. A 96-hour forecast point is shown for continuity but the system is likely to dissipate before that time.

Key Messages:

1. Willa is forecast to be a dangerous hurricane when it reaches the coast of southwestern mainland Mexico by late Tuesday or Wednesday bringing a life-threatening storm surge, damaging hurricane-force winds, and life-threatening flash flooding. A Hurricane Watch and tropical storm warnings and watches are in effect for a portion of the area. Residents in these areas should monitor the progress of this system and follow any advice given by local officials.

FORECAST POSITIONS AND MAX WINDS

INIT  21/2100Z 17.0N 107.0W  100 KT 115 MPH - Category 2 (WSW Lázaro Cárdenas, Mexico)
 12H  22/0600Z 17.8N 107.4W  120 KT 140 MPH - Category 4 (WSW Tecomán, Mexico)
 24H  22/1800Z 18.8N 107.6W  130 KT 150 MPH - Category 4 (WSW Manzanillo, Mexico)
 36H  23/0600Z 19.8N 107.6W  125 KT 145 MPH - Category 4 (WSW Puerto Vallarta, Mexico)
 48H  23/1800Z 21.0N 107.1W  110 KT 125 MPH - Category 3 (WNW Puerto Vallarta, Mexico)
 72H  24/1800Z 24.8N 103.3W   45 KT  50 MPH - Tropical Storm (Gral Simón Bolívar, Mexico)
 96H  25/1800Z 26.8N 100.0W   20 KT  25 MPH - Post tropical (Vallecillo, Mexico)
120H  26/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1200 PM MDT Sun Oct 21 2018

Hurricane Willa DISCUSSION AND OUTLOOK

At 1200 PM MDT (1800 UTC), the center of Hurricane Willa was located near latitude 16.8 North, longitude 106.9 West. Willa is moving toward the northwest near 7 mph (11 km/h), and this general motion is expected to continue today. A turn toward the north-northwest and north is expected by tonight and Monday. Willa is expected to accelerate toward the north-northeast and approach the southwestern coast of mainland Mexico by late Tuesday.

Maximum sustained winds have increased to near 105 mph (165 km/h) with higher gusts. Steady to rapid strengthening is forecast during the next day or so, and Willa is expected to become a major hurricane by Monday morning.

Hurricane-force winds extend outward up to 15 miles (30 km) from the center and tropical-storm-force winds extend outward up to 60 miles (95 km).

The estimated minimum central pressure is 971 mb (28.67 inches).

HAZARDS AFFECTING LAND

STORM SURGE: A dangerous storm surge and large and destructive waves are possible along portions of the coast of southwestern Mexico by Tuesday or Tuesday night.

WIND: Hurricane conditions are possible within the hurricane watch area by late Tuesday, with tropical storm conditions possible by Tuesday morning. Tropical storm conditions are possible within the tropical storm watch area by early Tuesday.

RAINFALL: Willa is expected to produce storm total rainfall accumulations of 5 to 10 inches, with local amounts to 15 inches, across portions of western Jalisco, western Nayarit, and southern Sinaloa in Mexico. This rainfall would cause life-threatening flash flooding and landslides.

Farther inland, Willa is expected to produce 2 to 4 inch amounts across portions of Zacateca, Durango, southeast Chihuahua, and Coahuila in Mexico, with local amounts to 6 inches possible. This rainfall could also cause life-threatening flash flooding.

SURF: Swells generated by Willa should begin to affect portions of the coast of southwestern and west-central Mexico by Monday. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office.

NWS National Hurricane Center Miami FL 900 AM MDT Sun Oct 21 2018

Hurricane Willa – First-light GOES-16 visible satellite imagery shows that Willa continues to become better organized, with a tightly coiled band of convection wrapping around the center. There has also been evidence of a small eye in recent microwave and infrared satellite pictures. Subjective and objective satellite intensity estimates range from 77 kt to 90 kt, and the initial intensity has been increased to 85 kt for this advisory.

Willa is moving northwestward or 325/6 kt. The track guidance continues to indicate that Willa will move northwestward today, then turn northward on Monday, and then head north-northeastward on Tuesday between a deep-layer ridge that extends westward from the Gulf of Mexico and an approaching mid-level trough. The dynamical model guidance remains in good overall agreement on this scenario, but there are differences in how quickly Willa will accelerate north-northeastward. The UKMET and ECMWF are much slower than the remainder of the dynamical models, with the GFS and GFS ensemble mean the fastest. The NHC track forecast brings the center of the Willa onshore of the coast of southwestern Mexico within 72 h, and it lies closest to the HFIP corrected consensus, which is a little faster than the other consensus aids.

The hurricane is expected to remain within low vertical wind shear and over warm waters of around 28 degrees Celsius during the next day or two. These very favorable conditions are expected to allow steady to rapid strengthening through Monday night, and the NHC forecast is near the upper end of the intensity guidance. By 48 hours, increasing southwesterly shear is forecast to initiate weakening, but Willa is likely to remain a very strong hurricane through landfall in southwestern Mexico. After landfall, rapid weakening and dissipation over the mountainous terrain of mainland Mexico should occur.

Key Messages:

1. Willa is forecast to be a hurricane when it reaches the coast of southwestern mainland Mexico by late Tuesday or Wednesday bringing a life-threatening storm surge, dangerous winds, and life-threatening flash flooding, and hurricane and tropical storm watches are now in effect for a portion of the area. Residents in the watch areas should monitor the progress of this system and follow any advice given by local officials.

FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 16.6N 106.7W   85 KT 100 MPH - Category 2 (WSW Zihuatanejo, Mexico)
 12H  22/0000Z 17.2N 107.2W   95 KT 110 MPH - Category 2 (WSW Lázaro Cárdenas, Mexico)
 24H  22/1200Z 18.2N 107.6W  110 KT 125 MPH - Category 3 (WSW Manzanillo, Mexico)
 36H  23/0000Z 19.3N 107.7W  120 KT 140 MPH - Category 4 (WNW San Patricio, Mexico)
 48H  23/1200Z 20.4N 107.5W  110 KT 125 MPH - Category 3 (WSW Puerto Vallarta, Mexico)
 72H  24/1200Z 23.3N 105.5W   80 KT  90 MPH - Category 1 (Pueblo Nuevo, Mexico)
 96H  25/1200Z 26.5N 101.0W   20 KT  25 MPH - Post Tropical (Mina, Mexico)
120H  26/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 300 AM MDT Sun Oct 21 2018

Tropical Storm Willa has continued to rapidly intensify based on a well-defined CDO with an intermittent pinhole eye evident in high-resolution GOES-16 infrared (IR) satellite imagery. Upper-level outflow has become well established in all quadrants. The intensity is difficult to ascertain since satellite intensity estimates vary widely based on the scene type used and also the small size of the hurricane. TAFB and SAB both provided an estimate of T4.0/65 kt, whereas UW-CIMSS ADT and SATCON were 67 kt and 56 kt, respectively. In contrast, NHC objective T-numbers are T5.0/90 kt using an embedded center and as high as T6.0/115 kt using a pinhole eye. Given that the eye has not been maintained in IR imagery, the advisory intensity of 75 kt lies between the subjective TAFB/SAB estimate and lower NHC objective estimate.

Willa is moving at 315/06 kt. There is no significant change to the previous forecast track reasoning. Willa is forecast to continue moving northwestward for the next 24 h or so, followed by a turn toward the north on Monday, with a motion toward the northeast expected on Tuesday as the hurricane gradually rounds the western periphery of the deep-layer ridge. By late Tuesday, Willa is forecast to accelerate northeastward ahead of a deep-layer trough that will be approaching Baja California, resulting in landfall along the west-central coast of Mexico on Wednesday. The latest 00Z model guidance is tightly packed about the previous forecast track, and only minor forward speed adjustments were required. A 96-h position has been provided only for continuity purposes, and Willa will likely have dissipated over the Mexican mountains by then.

Willa’s small inner-core wind field along with ideal environmental conditions consisting of low shear, high mid-level moisture, and warm SSTs of 28 deg C should allow the hurricane to continue to rapidly intensify for the next 24-36 hours, followed by a leveling off in the intensity by early Tuesday due to expected cold upwelling beneath the slow-moving hurricane. In 60-72 hours, increasing southwesterly shear ahead of the aforementioned deep-layer trough is expected to induce steady weakening until landfall occurs. Rapid dissipation over the mountainous terrain of mainland Mexico will occur after landfall. The official intensity forecast is a tad above the consensus models HCCA and FSSE, and is little below the robust Navy COAMPS-TC model forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  21/0900Z 16.2N 106.5W   75 KT  85 MPH - Category 1 (WSW Lázaro Cárdenas, Mexico)
 12H  21/1800Z 16.8N 107.0W   85 KT 100 MPH - Category 2 (WSW Lázaro Cárdenas, Mexico)
 24H  22/0600Z 17.6N 107.4W  100 KT 115 MPH - Category 3 (WSW Manzanillo, Mexico)
 36H  22/1800Z 18.7N 107.7W  115 KT 130 MPH - Category 4 (WSW Manzanillo, Mexico)
 48H  23/0600Z 19.8N 107.7W  120 KT 140 MPH - Category 4 (WSW Puerto Vallarta, Mexico)
 72H  24/0600Z 22.3N 106.1W   90 KT 105 MPH - Category 2 (WSW Playa Novillero, Mexico)
 96H  25/0600Z 26.9N 101.2W   25 KT  30 MPH - Tropical Depression (Monclova, Mexico)
120H  26/0600Z...DISSIPATED INLAND

NWS National Hurricane Center Miami FL 900 PM MDT Sat Oct 20 2018

Tropical Storm Willa has rapidly intensified since genesis occurred last night, and it is almost a hurricane. Geostationary satellite and microwave images indicate that banding features have become well established in all quadrants and the inner core has continued to organize. There is still no evidence of an eye feature, however. A blend of the latest satellite intensity estimates supports increasing the initial wind speed to 60 kt.

The latest satellite fixes indicate that Willa is now moving northwestward at about 5 kt. The storm is expected to gradually turn to the right as it moves around the western periphery of a mid-level ridge. In response, a northwestward motion should continue for another day or so, followed by a turn toward the north on Monday. After that time, a faster north-northeast to northeast motion is expected when a shortwave trough approaches the system. The latest model guidance, except for the UKMET, show Willa making a sharper northward turn and at a faster pace. The NHC track forecast has been adjusted accordingly to be in better agreement with the latest consensus aids. This forecast is again faster than the previous one and shows Willa making landfall over west-central Mexico in 72 to 96 hours.

The storm has taken advantage of near ideal environmental conditions of very low wind shear, high levels of moisture, and warm 29 deg C SSTs. These conditions are expected to prevail for another couple of days, and that should allow Willa to continue to strengthen rapidly. In fact, the SHIPS Rapid Intensification (RI) indices show about 90 percent chance of RI continuing during the next 24 hours. Based on this information and the latest model guidance, the NHC intensity forecast shows Willa becoming a major hurricane in a day or so. Some weakening is likely before Willa reaches the coast due to an increase in shear and a decrease in available moisture, but Willa is forecast to be a hurricane when it reaches the coastline. After landfall, rapid weakening is expected due to interaction with the rugged terrain.

FORECAST POSITIONS AND MAX WINDS

INIT  21/0300Z 15.7N 106.1W   60 KT  70 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  21/1200Z 16.1N 106.6W   80 KT  90 MPH - Category 1 (WSW Zihuatanejo, Mexico)
 24H  22/0000Z 16.9N 107.1W   95 KT 110 MPH - Category 2 (WSW Lázaro Cárdenas, Mexico)
 36H  22/1200Z 17.7N 107.5W  110 KT 125 MPH - Category 3 (WSW Manzanillo, Mexico)
 48H  23/0000Z 18.7N 107.8W  110 KT 125 MPH - Category 3 (WNW Puerto Vallarta, Mexico)
 72H  24/0000Z 20.7N 107.3W   90 KT 105 MPH - Category 2 (WNW Puerto Vallarta, Mexico)
 96H  25/0000Z 24.1N 104.2W   35 KT  40 MPH - Tropical Storm (Durango, Mexico)
120H  26/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 400 PM CDT Sat Oct 20 2018

Tropical Storm Willa appears to be wrapping up quickly, and the low-level center is now embedded beneath a ragged central dense overcast. ASCAT data from several hours ago indicated winds were as high as 40 kt, but more recent satellite estimates support an intensity between 45-55 kt, and the maximum winds are set at 50 kt for this advisory.

Willa has turned west-northwestward and slowed down, and the initial motion is estimated to be 295/5 kt. The cyclone is forecast to recurve around the western edge of a mid-level ridge that lies over Mexico during the next few days, and then accelerate northeastward into mainland Mexico by days 4 and 5 ahead of a broad mid-latitude trough. Compared to previous model runs, the new track guidance has sped up significantly and also now shows a sharper recurvature, both of which suggest that Willa’s hazards could reach the coast of Mexico sooner than originally thought. The GFS and ECMWF remain the fastest of the models, and although the updated NHC track forecast trends in their direction, it hangs back a bit to give some weight to the HWRF, HCCA, and Florida State Superensemble. Even with that consideration, the new forecast does bring Willa to the coast sooner than before.

The satellite signature suggests that the storm is organizing quickly and is probably in the beginning stages of rapid intensification (RI). The RI indices are even higher this afternoon than they were this morning, and incredibly, the HWRF, SHIPS, HCCA, and Florida State Superensemble all bring Willa near or at major hurricane intensity in 36 hours. The NHC forecast follows those models’ lead and indicates significant strengthening over the next couple of days. A peak in intensity is likely to occur between 48-72 hours, followed by some weakening due to lower oceanic heat content and increasing vertical shear. Despite the expected weakening, Willa is expected to reach the coast of west-central mainland Mexico as a hurricane in about 4 days.

FORECAST POSITIONS AND MAX WINDS

INIT  20/2100Z 15.2N 105.8W   50 KT  60 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  21/0600Z 15.5N 106.3W   65 KT  75 MPH - Category 1 (WSW Acapulco, Mexico)
 24H  21/1800Z 16.1N 106.9W   85 KT 100 MPH - Category 2 (WSW Zihuatanejo, Mexico)
 36H  22/0600Z 16.8N 107.4W  105 KT 120 MPH - Category 3 (WSW Lázaro Cárdenas, Mexico)
 48H  22/1800Z 17.6N 107.8W  110 KT 125 MPH - Category 3 (WSW Colola, Mexico)
 72H  23/1800Z 19.1N 108.1W  100 KT 115 MPH - Category 3 (WSW San Patricio, Mexico)
 96H  24/1800Z 22.0N 106.5W   80 KT  90 MPH - Category 1 (ENE Isla San Juanico, Mexico)
120H  25/1800Z 24.5N 103.5W   40 KT  45 MPH - Tropical Storm (Santa Clara, Mexico)

NWS National Hurricane Center Miami FL 1000 AM CDT Sat Oct 20 2018

Tropical Storm Willa – A GMI microwave pass over the depression at 0916 UTC revealed that a tight inner core has developed, with a cyan and pink ring noted in the low-level 37-GHz channel. Outer convective banding has also been increasing, and a consensus of the latest subjective and objective satellite intensity estimates supports raising the maximum winds to 35 kt and designating the cyclone as Tropical Storm Willa. On an historical note, this is the first time that at least 21 named storms have formed within the eastern Pacific basin since the 1992 season.

The microwave data suggest that Willa’s center is a little farther south than previously estimated, and the initial motion is calculated to be westward, or 270/8 kt. The storm is already located near the western periphery of a mid-level ridge which extends across northern and central Mexico, and Willa is expected to slowly recurve around the ridge axis during the next 4 days. By the end of the forecast period, a mid-latitude trough located over the western U.S. is likely to cause Willa to accelerate toward the northeast in the direction of mainland Mexico. All of the track models agree on this general scenario, but there are some differences on how wide a turn Willa makes while it recurves. There are also some speed differences that appear to be related to how strong Willa will be when the mid-latitude trough becomes the main steering driver. The NHC forecast is very close to the previous forecast during the first 48 hours. After that time, the forecast has been nudged eastward since the GFS and ECMWF models are both near or east of the multi-model consensus aids.

With a low-level ring already observed in microwave imagery, and Willa located in an environment of low shear and over very warm ocean water, the cyclone appears poised to go through a period of rapid intensification (RI). Several of the various RI indices are over 50 percent, and thus the NHC forecast favors the high end of the intensity guidance and explicitly shows rapid strengthening over the next 48 hours. Willa is expected to be moving more slowly by days 3 and 4 (about 3 kt), and upwelling of colder water could induce some weakening by that time. An increase in shear is likely to cause more significant weakening by the end of the forecast period. The new NHC intensity forecast is a bit higher than the previous forecast to account for the possibility of rapid intensification, and it shifts Willa’s expected peak intensity about a day earlier.

FORECAST POSITIONS AND MAX WINDS

INIT  20/1500Z 14.8N 105.7W   35 KT  40 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  21/0000Z 15.0N 106.5W   50 KT  60 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  21/1200Z 15.3N 107.3W   65 KT  75 MPH - Category 1 (WSW Acapulco, Mexico)
 36H  22/0000Z 15.8N 107.9W   80 KT  90 MPH - Category 1 (WSW Acapulco, Mexico)
 48H  22/1200Z 16.6N 108.5W   95 KT 110 MPH - Category 2 (WSW Manzanillo, Mexico)
 72H  23/1200Z 17.7N 109.0W  100 KT 115 MPH - Category 3 (WSW Manzanillo, Mexico)
 96H  24/1200Z 19.0N 109.0W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, Mexico)
120H  25/1200Z 22.0N 107.5W   75 KT  85 MPH - Category 1 (WNW Isla María Madre, Mexico)

NWS National Hurricane Center Miami FL 400 AM CDT Sat Oct 20 2018

Tropical Storm Willa – Corrected advisory number from 2 to 1 Various satellite data indicate that the area of low pressure that NHC has been monitoring off the coast of southern Mexico for thew past few days has acquired enough convective organization to be designated as a tropical depression, the twenty-fourth one of the very busy 2018 eastern North Pacific hurricane season. Although the depression is a sheared system, some banding features have recently developed south of the center, while overshooting cloud tops just west of the center are quite cold -85 to -91 deg C). The initial intensity is set to 30 kt based on a satellite intensity estimate of T2.0/30 kt from both TAFB and SAB.

The initial motion estimate is 280/08 kt, based primarily on passive microwave fixes and GOES-16 nighttime imagery. A gradual turn toward the west-northwest is expected by this afternoon, followed by a slower northwestward motion on Sunday as the system moves along the southwestern periphery of a weakening mid-level ridge. A slow northwestward motion is expected to continue into early next week while the ridge to the north changes little. On days 4 and 5, however, a series of weak shortwave troughs are forecast to move through the larger scale southwesterly flow locked in over the southwestern U.S. and northern Mexico, causing an erosion of the western portion of the ridge, which should allow the cyclone to gradually recurve northward and north-northeastward. The NHC model guidance is in good agreement overall on this developing track scenario, and the official forecast track lies between the HCCA and TVCE track consensus aids.

The depression is expected to steadily strengthen during the next 96 hours due to very favorable environmental conditions consisting of low vertical wind shear (less than 10 kt), high amounts of mid-level moisture, and warm 28-30 deg C SSTs. As a result, the cyclone is expected to become a tropical storm later this morning, a hurricane by Sunday night, and be near major hurricane strength by Wednesday. Given the very favorable conditions expected on Sunday and Monday, there is a fair chance of rapid intensification occurring similar to that depicted by the COAMPS-TC and HMON models, which bring the cyclone to category-4 status around 72 hours. The NHC official intensity forecast near the HCCA and IVCN consensus models through 96 hours, and then a little above the guidance at 120 hours despite an increase in the shear expected at that time.

FORECAST POSITIONS AND MAX WINDS

INIT  20/0900Z 15.1N 104.9W   30 KT  35 MPH - Tropical Storm (WSW Acapulco, Mexico)
 12H  20/1800Z 15.5N 105.7W   40 KT  45 MPH - Tropical Storm (WSW Acapulco, Mexico)
 24H  21/0600Z 15.9N 106.6W   50 KT  60 MPH - Tropical Storm (WSW Acapulco, Mexico)
 36H  21/1800Z 16.5N 107.4W   60 KT  70 MPH - Tropical Storm (WSW Zihuatanejo, Mexico)
 48H  22/0600Z 17.1N 108.0W   75 KT  85 MPH - Category 1 (WSW Manzanillo, Mexico)
 72H  23/0600Z 18.0N 109.0W   90 KT 105 MPH - Category 2 (ESE Isla Socorro, Mexico)
 96H  24/0600Z 19.2N 109.4W  100 KT 115 MPH - Category 3 (WSW Tomatlán, Mexico)
120H  25/0600Z 21.7N 108.5W   95 KT 110 MPH - Category 2 (ESE Cabo San Lucas, Mexico)

NWS National Hurricane Center Miami FL 500 PM PDT Fri Oct 19 2018

For the eastern North Pacific…east of 140 degrees west longitude: The National Hurricane Center is issuing advisories on recently upgraded Tropical Storm Vicente, located just offshore the Pacific coast of Guatemala.

Showers and thunderstorms associated with an area of low pressure centered a few hundred miles south-southwest of Zihuatanejo, Mexico continue to show signs of organization. Environmental conditions are expected to remain favorable for further development, and a tropical depression is expected to form tonight or tomorrow while the low moves west-northwestward at about 10 mph, well offshore of the coast of southwestern Mexico.

* Formation chance through 48 hours…high…90 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 1100 AM PDT Fri Oct 19 2018

For the eastern North Pacific…east of 140 degrees west longitude: The National Hurricane Center has initiated advisories on Tropical Depression Twenty-Three-E, located just offshore of the Pacific coast of Guatemala.

Tropical Storm Willa Forming  – Showers and thunderstorms associated with an area of low pressure centered a few hundred miles south-southwest of Zihuatanejo, Mexico, are gradually becoming better organized. Environmental conditions are expected to become increasingly favorable for further development, and a tropical depression is expected to form later today or tomorrow while the low moves west-northwestward at about 10 mph, well offshore of the coast of southwestern Mexico.

* Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Fri Oct 19 2018

For the eastern North Pacific…east of 140 degrees west longitude:

 Showers and thunderstorms associated with a low pressure system centered less than 100 miles off the coast of Guatemala continue to show signs of organization, and it is possible that a tropical depression could be forming. If this trend continues, then advisories could be initiated on this system later today.

This disturbance is forecast to move generally westward near the coast of southern Mexico, and interests in that area should monitor the progress of the low during the next several days.

* Formation chance through 48 hours…high…70 percent. * Formation chance through 5 days…high...80 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Thu Oct 18 2018

For the eastern North Pacific…east of 140 degrees west longitude:

A trough of low pressure has developed within a large area of disturbed weather that extends from Central America westward to south of the Gulf of Tehuantepec. Some gradual development of this system is possible over the next few days while it moves slowly westward, near the coast of southern Mexico.

Additional information on the broad area of disturbed weather that extends from Central America to south of the Gulf of Tehuantepec can be found in High Seas Forecasts issued by the National Weather Service.

* Formation chance through 48 hours…low…10 percent. * Formation chance through 5 days…low...20 percent.

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