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.