Although the upper level wind shear is increasing over Hurricane Vance it has maintained its intensity today.  At 10:00 p.m. EST on Monday the center of Hurricane Vance was located at latitude 17.4°N and longitude 110.6°W which put it about 485 miles southwest of Mazatlan, Mexico.  Vance was moving toward the north-northeast at 13 m.p.h.  The maximum sustained wind speed was 110 m.p.h. and the minimum surface pressure was 965 mb.  A Tropical Storm Watch has been issued for the portion of the coast from Mazatan to Topolobampo, Mexico.

An upper level trough approaching southern California is generating southwesterly winds that are starting to affect Hurricane Vance.  The outflow is being inhibited on the western side of the hurricane and the upper level cirrus clouds show indications of being pushed toward the northeast.  It is possible that the circulation around Vance is beginning to tilt toward the northeast with height.  In addition, it looks like some drier air may be wrapping around the southwestern side of the circulation.  Increased wind shear and drier air should start weakening Vance and the shear could be strong enough to weaken it quickly at times.

The southwesterly winds in the upper level trough are expected to pull Vance toward the northeast and the center could reach the coast of Mexico in 36-48 hours.  Vance is likely to be much weaker when it gets to the coast but a Tropical Storm Watch has been issued as a precaution.  Moisture associated with the circulation around Vance is likely to enhance the rainfall over parts of Mexico during the middle portion of the week.