Tropical Storm Darby 5pm Update

Darby’s satellite signature has improved somewhat since the previous advisory, with a curved convective band wrapping into the center from the north, and outflow increasing in the north and northwest semicircles.

darby 721 5pm

The initial motion for this advisory is estimated to be 270/11 kt, with Darby currently being steered by a retrograding mid-level ridge centered well north of Hawaii.  This ridge will be the primary steering mechanism over the next day or so, after which time a deep

layer low digging southward will weaken the ridge, resulting in a reduction in Darby’s forward speed.  As the ridge weakens, Darby is expected to turn toward the northwest, but the turn is not expected to be a sharp as earlier forecast.

As Darby begins to gain latitude, it will move north of a mid-level ridge axis extending toward Hawaii from the eastern Pacific, and become embedded within deep-layer south to southeast flow that takes Darby toward the northwest.  Latest track guidance shifted toward the previous forecast, and the new track forecast is essentially an update of the previous one.

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