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Hurricane Blanca Weakens and Heads Toward Baja California

A combination of upwelling of cooler water and a possible eyewall replacement weakened Hurricane Blanca on Thursday.  At 11:00 p.m. EDT on Thursday the center of Hurricane Blanca was located at latitude 13.7°N and longitude 105.7°W which put it about 690 (1115 km) miles south-southeast of Cabo San Lucas, Mexico and about 380 (610 km) miles south-southwest of Manzanillo, Mexico.  Blanca was moving toward the north-northwest at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were gusts to 120 m.p.h. (195 km/h).  The minimum surface pressure was 975 mb.  The Hurricane Intensity Index (HII) was 16.5, the Hurricane Size Index (HSI) was 16.1 and the Hurricane Wind Intensity Size Index was 32.6.

The structure of Hurricane Blanca underwent a significant transformation on Thursday.  After being nearly stationary for approximately three days, the winds of Blanca stirred up the water in the upper ocean and mixed cooler water to the surface.  The cooler water reduced the energy available to drive the circulation of Blanca.  In addition, Blanca may have undergone an eyewall replacement cycle on Wednesday night and Thursday morning.  When a rainband wraps around an existing eyewall, it produces dissipation of the original eyewall.  The result is often a larger hurricane with a bigger eye, which is the appearance of Blanca on satellite imagery.  The combination of cooler water and a possible eyewall replacement changed the structure of the hurricane from a small intense circulation to a weaker and larger circulation.  However, Blanca is still a 100 m.p.h. (160 km/h).  Blanca is moving again and it will start to move away from the region of cooler water.  The upper level winds are relatively light and the environment is favorable for some intensification during the next day or two.  Since Blanca is larger and less well organized, it will respond more slowly to the favorable environment.  As the hurricane nears latitude 20°N, it will start to encounter cooler water and weaken will be likely.

A ridge to the northeast of Blanca and a trough west of Baja California are combining to steer it toward the north-northwest.  That steering pattern is likely to continue for the next several days.  On its anticipated track Blanca would approach the southern portion of Baja California in about three days.  A reconnaissance aircraft is scheduled to investigate the hurricane on Friday.

Hurricane Blanca Rapidly Intensifies To Category 4

Hurricane Blanca intensified very rapidly on Wednesday into a Category 4 hurricane on the Saffir-Simpson Scale.  At 5:00 p.m. EDT on Wednesday the center of Hurricane Blanca was located at latitude 12.3°N and longitude 104.7°W which put it about 810 miles (1300 km) south-southeast of Cabo San Lucas, Mexico and about 465 miles (745 km) south of Manzanillo, Mexico.  Blanca drifted slowly southward during the day, but it is essentially stationary.  The maximum sustained wind speed was 140 m.p.h. (220 km/h) and there were gusts to 165 m.p.h. (270 km/h).  The minimum surface pressure was 945 mb.  Blanca had a Hurricane Intensity Index (HII) of 28.3, a Hurricane Size Index (HSI) of 8.6 and a Hurricane Wind Intensity Size Index (HWISI) of 36.9.  Blanca is almost as strong and slightly larger than Hurricane Charley was when it hit southwest Florida in 2004.  At that time Charley had a HII of 29.9, a HSI of 7.7 and a HWISI of 37.6.

Blanca intensified from 75 m.p.h. (120 km/h) to 140 m.p.h. (220 km/h) during the past 24 hours which is a very rapid rate of intensification.  However, it is nowhere near the record for rapid intensification over the Eastern North Pacific.  In 1997 the maximum sustained wind speed in Hurricane Linda increased from 75 m.p.h. (120 km/h) to 175 m.p.h. (290 km/h) in a 24 hour period.  Blanca’s relatively small size means that there is less mass to accelerate in order to increase the wind speed.  It has efficiently extracted energy from the upper ocean and the wind speed in the small inner core increased rapidly today.  It is over water where the Sea Surface Temperature (SST) is near 30°C.  If Blanca were to remain stationary long enough, its winds would mix some cooler water to the surface.  Some subsidence and drier air is approaching the northwestern periphery of Blanca, but that air appears to have not had an effect on the core of the hurricane today.  Upper level winds are light right over the center of Blanca and there is little vertical wind shear over its inner core.  As long as Blanca can extract sufficient energy from the upper ocean, the potential for further intensification exists.  Much of the guidance suggests that Blanca could intensify for another 12 to 24 hours.  However, eyewall replacement cycles can occur in strong hurricanes and cause fluctuations in intensity.  Changes in intensity in small hurricanes can occur rapidly as we have seen today.  Eventually, when Blanca starts to move northward, it will encounter cooler SSTs and more wind shear which will cause it to weaken.

A ridge over Baja California is preventing Blanca from moving toward the north.  The hurricane is in an area where the steering currents are weak, which resulted in a slow southward drift today.  The ridge is forecast to shift to the east during the next several days and it will start to steer Blanca toward the northwest.  On its anticipated track Blanca could approach the southern tip of Baja California late in the weekend.  Because of a possible threat to Baja California a reconnaissance plane has been scheduled to investigate Blanca on Friday.  Blanca will weaken before it approaches that area, but it may still posed a significant risk.

Blanca Intensifies Into a Hurricane

The structure of Tropical Storm Blanca continued to improve on Tuesday and it intensified into a hurricane.  At 5:00 p.m. EDT on Tuesday the center of Hurricane Blanca was located at latitude 13.1°N and longitude 104.6°W which put it about 375 miles (605 km) south-southwest of Zihuatanejo, Mexico and about 410 miles (655 km) south of Manzanillo, Mexico.  Blanca was stationary.  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 960 mb.  The Hurricane Intensity Index (HII) was 10.4, the Hurricane Size Index (HSI) was 5.8 and the Hurricane Wind Intensity Size Index (HWISI) was 16.2.  Since Blanca and Andres both became hurricanes this year, June 2 becomes the earliest date on record by which time two hurricanes formed over the Eastern North Pacific Ocean.  However, it should be noted that the most reliable records only go back to 1971.

Hurricane Blanca is sitting over water where the Sea Surface Temperature (SST) is near 30°C.  It is efficiently extracting energy from the upper ocean and that energy is fueling its intensification.  Spiral bands of thunderstorms are well organized and the strongest storms are near the center of circulation.  The thermodynamic environment is very favorable for further intensification and rapid intensification is possible.  There are a several of factors that could slow the rate of intensification at times.  Upper level outflow from Hurricane Andres, which is about a thousand miles west of Blanca, appears to be generating some vertical wind shear on the northern and western sides of Blanca.  Thunderstorms in Blanca are producing upper level divergence, but some of the divergence may be reduced in the northwestern quadrant of the hurricane.  Andres is slowly spinning down and the wind shear is likely to lessen during the next several days.  A second potential inhibiting factor is the fact that Blanca is not moving much.  The warm water underneath Blanca is relatively deep, but if it sits in one location long enough, its winds will eventually begin  to mix some cooler water to the surface.  For the time being Blanca has sufficient energy in the upper ocean to support further intensification.  Once Blanca starts moving, then it will be over warm SSTs until it approaches latitude 20°N.  Finally, if Blanca gets as strong as some guidance suggest it could, then eyewall replacement cycles also could produce fluctuations in intensity.  As I mentioned above, Blanca is likely to intensify further and it could intensify rapidly at times.

A ridge in the middle levels centered near Baja California is blocking the northward progress of Blanca and the hurricane is in an area where the steering currents are weak.  The ridge is forecast to move slowly eastward toward a position over northern Mexico and Texas.  As the ridge moves eastward it will initially steer Blanca toward the northwest.  In several days the ridge will cause Blanca to turn more toward the north.  On its anticipated track, Blanca could approach the southern tip of Baja California in a few days.  It is too early to know how strong Blanca might be at that time or how much of a risk it might pose to that area.

Tropical Depression Two-E Strengthens to Tropical Storm Blanca

Despite vertical wind shear caused by the outflow from Hurricane Andres, the low level circulation of Tropical Depression Two-E continued to consolidate and the National Hurricane Center upgraded the system to Tropical Storm Blanca.  At 11:00 a.m. EDT on Monday the center of Tropical Storm Blanca was located at latitude 13.5°N and longitude 104.1°W which put it about 335 miles (540 km) south-southwest of Zihuatanejo, Mexico.  Blanca was moving toward the northwest at 5 m.p.h. (7 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1004 mb.

Upper level divergence from Hurricane Andres, which is about 1000 miles west of Blanca, is still generating some vertical wind shear over the top of Blanca.  However, the strongest upper level outflow and wind shear is now several hundred miles north of the tropical storm.  As a result, Blanca has been able to efficiently extract energy from the upper ocean and it has generated many more thunderstorms in recent hours.  The circulation has developed spiral bands and an inner core of convection.  The strong thunderstorms near the core appear to be generating some upper level outflow which is pumping out mass and causing the surface pressure to decrease.  Blanca is over water where the Sea Surface Temperature is near 30°C and there is a lot of energy in the upper ocean.  Blanca is likely to intensify and it could intensify rapidly if the magnitude of the wind shear remains moderate or low.

Blanca is being steered slowly toward the northwest by a ridge over northern Mexico, but the steering currents are relatively weak.  The ridge is expected to strengthen during the week and steer Blanca toward the northwest or north-northwest.  On its anticipated track Blanca poses no immediate threat to Mexico.  However, it could approach Baja California or the western coast of Mexico later this week.

Andres Strengthens Into a Category 4 Hurricane

Hurricane Andres turned westward and strengthened rapidly into a Major Hurricane on Sunday.  At 11:00 p.m. EDT on Sunday the center of Hurricane Andres was located at latitude 15.3°N and longitude 119.2°W which put it about 800 miles southwest of the southern tip of Baja California.  Andres was moving toward the west at 6 m.p.h.  The maximum sustained wind speed was 140 m.p.h. (220 km/h) which made Andres a Category 4 hurricane on the Saffir-Simpson Scale.  There were gusts to 165 m.p.h. (265 km/h) and the minimum surface pressure was 943 mb.   Andres became only the fifth Major Hurricane to form over the Eastern North Pacific during the month of May.

By turning toward the west Hurricane Andres remained over water where the Sea Surface Temperature (SST) was 27°C.  The westward movement also minimized the vertical wind shear.  The combination of warm SST and little vertical wind shear produced rapid intensification.  Andres could remain over warm SSTs for another day or so.  Eventually it will encounter cooler water, which will be unable to supply enough energy to maintain its current intensity.  There are stronger upper level winds west of Andres and those will increase the vertical wind shear over the hurricane.  Cooler SSTs and more shear will weaken Andres during the coming week.

A strengthening ridge steered Andres toward the west on Sunday.  Another upper level trough will approach the ridge during the next few days.  The trough is likely to weaken the ridge and cause Andres to turn more northward again.  Track guidance from the numerical models diverges later in the week and the uncertainty increases at longer time periods.

Tropical Depression Two-E Forms West of Mexico

Thunderstorms developed near a low level circulation on Sunday evening and the National Hurricane Center classified the system as Tropical Depression Two-E (TD2E).  At 11:00 p.m. EDT on Sunday the center of TD2E was located at latitude 12.7°N and longitude 103.3°W which put it about 365 miles south-southwest of Zihuatanejo, Mexico.  TD2E was moving toward the west-northwest at 5 m.p.h.  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were gusts to 45 m.p.h. (70 km/h).  The minimum surface pressure was 1006 mb.

The intensity forecast for TD2E is quite challenging.  Upper level outflow from Hurricane Andres, which is about 1000 miles west of TD2E, is creating strong vertical wind shear over the top of the depression.  The low level circulation of TD2E was completely exposed at times on Sunday afternoon as the higher level clouds were blown away from it.  At other times thunderstorms developed quickly near the center of circulation.  As long the outflow from Andres blows over the top of TD2E, it will inhibit intensification.  On the other hand, the depression is over water where the Sea Surface Temperature (SST) is near 30°C and there is a lot of energy in the upper layer of the ocean.  Hurricane Andres is likely to weaken and move farther away from TD2E during the next few days.  If that happens, then the vertical wind shear over TD2E will decreases.  If the lower level structure of the depression is still intact at that time, then it will be able to extract energy from the ocean and intensify.  Guidance from numerical models predicts TD2E will survive and intensify later this week.

The track forecast is also challenging because it is partly dependent on the vertical height of the structure of the depression.  If the depression is weak and shallow, it will be steered more by winds in the lower levels.  Those winds would tend to steer it toward the west-northwest.  If the depression intensifies and grows taller, it will be steered by winds higher in the atmosphere.  Fluctuations in the amount of vertical wind shear and its subsequent effects on the intensity of TD2E could result in erratic motion for several days.

Andres Gets Close To Major Hurricane Status

Hurricane Andres strengthened quickly on Saturday and it came close to reaching Major Hurricane status.  At 11:00 p.m. EDT on Saturday the center of Hurricane Andres was located at latitude 15.1°N and longitude 116.8°W which put it about 700 miles southwest of the southern tip of Baja California.  Andres was moving toward the northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 110 m.p.h. (175 km/h) and there were gusts to 130 m.p.h. (210 km/h).  The minimum surface pressure was 966 mb.

The convection near the center of Hurricane Andres continued to strengthen for much of Saturday and the eye exhibited circular symmetry.  The hurricane was moving over water where the Sea Surface Temperature (SST) was near 28°C and there was sufficient energy in the upper ocean to support a strong hurricane.  The upper level winds were relatively light and there was not much vertical wind shear over the center of circulation.  However, Andres may be near its maximum intensity.  There are cooler SSTs to the northwest of the hurricane and it will gradually move over those cooler SSTs.  As it moves over cooler water, Andres will also pull cooler, more stable air into the northwestern part of the circulation.  Cooler water and more stable air are likely to weaken the circulation on Sunday.   There are also stronger upper level westerly winds near latitude 20°N and so Andres will encounter stronger vertical wind shear early next week, which could speed its weakening trend.

A trough passing north of the ridge that has been steering Andres has weakened the ridge and caused the hurricane to turn toward the northwest.  Once the trough moves farther east, the ridge will strengthen and extend westward.  The building ridge will cause Andres to move more toward the west during the early part of next week.  On its anticipated track Andres poses no threat to Mexico.

Andres Intensifies Into a Hurricane

The core of the circulation of Andres became more circular and symmetrical on Friday and an eye has been visible intermittently during the day.  The National Hurricane Center classified Andres as a hurricane in its 5:00 p.m. EDT advisory on Friday.  At that time the center of Hurricane Andres was located at latitude 12.8°N and longitude 114.8°W which put it about 770 miles south-southwest of the southern tip of Baja California, Mexico.  Andres was moving toward the northwest at 7 m.p.h.  The maximum sustained wind speed was 75 m.p.h. and there were wind gusts to 90 m.p.h.  The minimum surface pressure was 990 mb.

As the circulation consolidated in the center of Andres strong thunderstorms pushed higher into the atmosphere around the eye.  Those thunderstorms pumped mass away from the center and caused the pressure at the surface to decrease.  Andres is over water where the Sea Surface Temperature (SST) is between 28°C and 29°C which means there is enough energy in the upper ocean to support further intensification.  It also remains in an area where the vertical wind shear is low.  So, further intensification is likely during the next day or two.  As Andres moves farther north, it will gradually move over cooler SSTs and when it gets near latitude 20°N it will begin to be affected by upper level southwesterly winds.  Cooler SSTs and more wind shear will likely cause Andres to weaken during the early part of next week.

Andres is near a weakness in the mid-level ridge that has been steering the hurricane.  The weakness in the ridge caused Andres to turn toward the northwest and its forward speed to decrease.  After an upper level trough moves east of the ridge in a day or two, the ridge will strengthen and extend westward.  That will cause Andres to move more toward the west again.  On its anticipated track Andres poses no threat to Mexico.

TD One-E Intensifies Quickly Into Tropical Storm Andres

A favorable environment caused Tropical Depression One-E to intensify quickly into Tropical Storm Andres on Thursday.  At 11:00 p.m. EDT on Thursday the center of Tropical Storm Andres was located at latitude 11.8°N and longitude 113.3°W which put it about 800 miles south-southwest of the southern tip of Baja California.  Andres was moving toward the west-northwest at 10 m.p.h.  The maximum sustained wind speed was 70 m.p.h. and there were gusts to 85 m.p.h.  The minimum surface pressure was 994 mb.

Andres exhibits a more organized circulation pattern on satellite imagery.  The end of the primary rainband wrapped completely around the center of circulation and an eye appears on some satellite images.  There are more thunderstorms in the rainbands and upper level outflow continues in all directions.  Andres is moving over water where the Sea Surface Temperature (SST) is near 29°C.  Although there are strong upper level westerly winds north of 20°N and brisk upper level easterly winds near the Equator, Andres is moving through a region where the upper level winds are light.  There is little vertical wind shear to inhibit the  intensification of Andres during the next day or so.  It will gradually move over water where the SSTs are slightly cooler, but there should still be plenty of energy in the upper ocean to support further intensification.  Andres is likely to become a hurricane on Friday and it could continue to intensify rapidly for another 12 to 24 hours.

An upper level trough passing well to the north of Andres is weakening the ridge that has been steering Andres toward the west-northwest.  The effect of the trough will likely be to slow the forward motion of Andres and temporarily make it move more toward the northwest.  After the upper level trough moves off to the northeast, the ridge is likely to strengthen again.  As the ridge strengthens, it will start to steer Andres more toward the west.  On its projected track Andres poses no current threat to Mexico.

 

Tropical Depression One-E Forms Southwest of Mexico

A well developed cyclonic circulation formed at the surface in a large area of thunderstorms southwest of Mexico and the National Hurricane Center classified the system as Tropical Depression One-E.  At 5:00 a.m. EDT on Thursday the center of Tropical Depression One-E (TD1E) was located at latitude 11.0°N and longitude 110.4°W which put it about 685 miles southwest of Manzanillo, Mexico.  TD1E was moving toward the west-northwest at 15 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and there were gusts to 45 m.p.h.  The minimum surface pressure was 1005 mb.

The circulation around TD1E is still in the organizational stage and there are more strong thunderstorms in the southern half of the circulation.  TD1E is in an environment that is very favorable for intensification.  It is moving over water where the Sea Surface Temperatures (SSTs) are around 29°C to 30°C.  It is an area between upper level easterly winds near the Equator and stronger upper level westerly winds farther north.  There are lighter upper level winds over TD1E and the light winds allowed it to develop strong upper level outflow in all directions.  Warm SSTs and strong upper level divergence should allow TD1E to intensify during the next several days and a period of rapid intensification is quite possible once the circulation is fully organized.

An upper level ridge to the northeast of TD1E is steering it toward the west-northwest.  As TD1E gets closer to a weakness in the western portion of the ridge, it is expected to turn toward the northwest and slow down.  On its anticipated path TD1E poses no immediate threat to the west coast of Mexico.