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.