Former Hurricane Vance weakened to a tropical storm on Sunday as it moved over the Eastern North Pacific Ocean south of Mexico.  At 11:00 p.m. EDT on Sunday the center of Tropical Storm Vance was located at latitude 15.0°N and longitude 104.7°W which put the center about 275 miles (445 km) south of Manzanillo, Mexico.  Vance was moving toward the northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 65 m.p.h. (105 km/h) and there were wind gusts to 80 m.p.h. (130 km/h).  The minimum surface pressure was 995 mb.

Former Hurricane Vance weakened to a tropical storm on Sunday.  An upper level trough over Baja California was producing southwesterly winds that were blowing toward the top of Vance’s circulation.  Those winds were causing strong vertical wind shear.  The strong vertical wind shear caused Vance to weaken to a tropical storm.

The strong vertical wind shear also caused the distribution of thunderstorms in Tropical Storm Vance to become asymmetrical.  Thunderstorms were still occurring in bands in the northeastern part of Vance’s circulation.  Bands in the other parts of Tropical Storm Vance consisted primarily of showers and lower clouds.  Storms near the center of Vance generated upper level divergence that pumped mass away to the northeast of the tropical storm.  The removal of mass in the upper levels was less than the convergence of mass in the lower levels of the atmosphere.  So, the surface pressure increased on Sunday.

The distribution of wind speeds in Tropical Storm Vance was also asymmetrical.  Winds to tropical storm force extended out 150 miles (240 km) in the northern side of Vance’s circulation.  Winds to tropical storm force extended out 80 miles in the southern side of Tropical Storm Vance.

Tropical Storm Vance will move through an environment that will be unfavorable for intensification during the next 24 hours.  Vance will move over water where the Sea Surface Temperatures are near 29°C.  However, the upper level trough over Baja California will continue to cause strong vertical wind shear.  Tropical Storm Vance is likely to continue to weaken on Monday because of the strong vertical wind shear.

Tropical Storm Vance will move around the western end of a high pressure system that is over Mexico.  The high pressure system will steer Vance slowly toward the northwest during the next 24 hours.  On its anticipated track, Tropical Storm Vance will remain southwest of Mexico for the next several days.