Thursday, September 13, 2018

Hurricane Florence Update

Here’s the latest from Weather Underground.

Hurricane Florence’s peak winds have fallen to Category 3 strength, but the storm remains a catastrophic rainfall threat and significant storm surge and wind threat to the Southeast U.S. Florence is expected to stall on Friday and move slowly west-southwestward along or just inland of the coast for several days, bringing a catastrophic rainfall well inland, and a destructive storm surge and wind event along a considerable swath of the North and South Carolina coasts.

The Hurricane Hunters and microwave satellite imagery this afternoon found that Florence was not able to recover from this morning’s eyewall replacement cycle (ERC). During this phenomenon, common in intense hurricanes, the eye shrinks to such a small diameter that the eyewall becomes unstable and collapses. The hurricane then creates a new larger-diameter eyewall out of a spiral band. During this process, the peak winds typically fall by 10 – 15 mph, and the central pressure can rise 10 – 15 mb. Florence was never able to rebuild its inner core after this morning’s ERC, though, and data from the Hurricane Hunters and satellites have shown large gaps in the eyewall this afternoon.

As a result, Florence has not been able to concentrate a major portion of its wind energy into an intense eyewall, and the hurricane’s wind energy has spread out over a larger area. This will reduce the potential wind damage from the storm at landfall, but will allow a larger storm surge to build. At 5 pm EDT Wednesday, Florence’s tropical storm-force winds had expanded, and extended out up to 195 miles from the center; hurricane-force winds extended out up to 70 miles. For comparison, at landfall, Hurricane Katrina’s tropical storm-force and hurricane-force winds extended out up to 230 miles and 125 miles from the center, respectively.

It’s big and slow-moving.  Those are two qualities you do not want in a hurricane.  To put it in perspective, if the eye of the storm was over Miami, they’d be feeling hurricane-force winds as far away as Palm Beach to the north and Marathon in the Keys to the south, and the storm effects would be knocking over things in Orlando.

Speak!