Although strong vertical wind shear is weakening Hurricane Hilda, its proximity to Hawaii has prompted the issuance of a Tropical Storm Watch.  At 11:00a.m. EDT on Tuesday the center of Hurricane Hilda was located at latitude 17.5°N and longitude 151.3°W which put it about 290 miles (470 km) east-southeast of Hilo, Hawaii.  Hilda was moving toward the northwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 85 m.p.h. (140 km/h) and there were wind gusts to 100 m.p.h. (160 km/).  The minimum surface pressure was 985 mb.  The Central Pacific Hurricane Center in Honolulu has issued a Tropical Storm Watch for Hawaii County.

An upper level low north of the Hawaiian Islands is creating strong southwesterly winds that are blowing straight into Hurricane Hilda.  Although the circulation of Hilda appeared strong enough on Monday to deflect the upper level winds around it, those winds are tilting the vortex significantly to the east with height today.  The middle and upper portions of the hurricane’s circulation appear to still be attached to the lower level circulation, but they are tilted toward the east.  If the upper level winds get much stronger they could shear off the upper portion of the circulation from the lower level circulation.  The effect of the strong vertical wind shear is weakening Hurricane Hilda and that weakening is expected to continue during the next several days.  Hilda could weaken to tropical storm status within 24 hours and it could be a tropical depression in 48 to 72 hours.

A subtropical ridge northeast of Hilda and the upper low north of Hawaii are both affecting the movement of the hurricane.  The subtropical ridge is trying to push Hurricane Hilda toward the west, while the upper low is trying to push it to the northeast..  The combined effects of the ridge and the low are causing Hilda to move slowly northwestward.  If the strong upper level winds do shear the top off of Hilda, then winds in the lower atmosphere will steer the surface circulation toward the west.  Since Hilda could still be a minimal tropical storm when it approaches the Big Island of Hawaii, a Tropical Storm Watch has been issued.