Hurricane Lane Fell Apart as it Approached Hawaii. So What Happened?

Lane's appearance on satellite imagery deteriorated rapidly from a well-defined Category 5 hurricane to a disheveled tropical storm over the course of a few days late last week. But why did this weakening occur and spare Hawaii from additional severe impacts?

(MORE: Recapping Hurricane Lane)

First and foremost, Lane encountered a wall of wind shear as it moved closer to Hawaii. Wind shear, a change in wind speed and/or direction with height, is an enemy to hurricanes since it can shred them apart when strong and persistent.

You can see Lane move from an area of light wind shear (blue and green shadings) to higher wind shear (orange and red shadings) in the animation below from Aug. 22-24.

Those strong winds also imported dry air, another nemesis of hurricanes, into the core of Lane, according to a tweet from Philippe Papin, an atmospheric scientist at the U.S. Naval Research Laboratory.

The wind shear and dry air attacked Lane's core, or eyewall, leading to the degradation of its center of circulation as shown in this animation.

When Lane entered that zone of strong winds, however, it was over.

Another potential factor in Lane's weakening is the interaction of its circulation with Hawaii's mountainous terrain. The low-level wind flow around the hurricane might have been disrupted by the tall peaks, assisting in Lane's demise.

Forecasters always knew Lane would encounter wind shear, but the question was how quickly it would surrender to the strong winds and begin to fall apart.

That had implications for how close Lane would get to the Hawaiian Islands. Slower weakening would allow Lane to come closer to Hawaii while rapid weakening would keep it farther south.

Thankfully, Lane weakened faster and therefore turned to the west (left) before reaching the islands. Weaker circulations tend to follow the path of prevailing winds in the lower atmosphere, which, in this case, were from the east.

Although the heavy rain from Lane produced significant flooding and landslides on the Big Island, impacts from strong winds and storm surge could have been much worse across the island chain had Lane held intact longer.