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Comments on the Remnants of Hurricane Ike by Dr. Jay Hobgood of The Ohio State University.

First, Ike was a very large hurricane when it made landfall in Texas. Hurricane force winds extended out more than 100 miles on the right side and tropical storm force winds extended out over 200 miles. So it had a lot of kinetic energy and inertia when it moved inland.

Second, Ike had a double eyewall structure for much of its existence as a tropical cyclone. I am attaching a jpg file that shows several satellite images constructed from sensors using different portions of the electromagentic spectrum. If you look at the bottom two images, you can see the double eyewall strcture. The inner circle is the inner eye and the ring around it is the inner eyewall where the strongest wind were for much of Ike's existence. Then there is another ring, which is the outer eye or "moat" as it is sometimes called. Then there is a thin outer ring, that is the outer eyewall. The winds in the outer eyewall were almost as strong as those in the inner eyewall.

Normally, the outer eyewall cuts off the flow to the inner eye, which dissipates during what is called an eyewall replacement cycle that takes 12-36 hours. Then the outer eye starts to constrict and the circulation gets smaller. In Ike, the inner eye didn't dissipate until 6-12 hours before landfall, despite the fact that Ike crossed both eastern and western Cuba. Thus, the wind field stayed large right up until landfall.

Third, there were significantly higher winds above the surface that were not transported down to the ground before Ike made landfall. Reports from numerous reconnaissance flights reported much stronger winds at flight level that were not translating to the surface. In addition an anemometer located 122 meters above sea level on an oil rig reported winds at 130-135 m.p.h., while the surface winds were 105 m.p.h. The higher winds speed just above the surface may explain some of the wind damage to his rise structures in Houston.

Moving to Ike's effect on Ohio.

Ike still had a minimum sea leavel pressure of 986-990 mb as it moved northwest of Ohio. Ike was also in the middle of a transition from a tropical cyclone to an extratropical cyclone. So, it may have had an infusion of baroclinic energy. However, it seems to me that the big thing was that the stronger winds aloft were finally translated down to the ground as Ike moved over Ohio. Since we didn't have any thunderstorms when Ike went through, it isn't likely that thunderstorm downdrafts were the source of the high winds. The more likely cause was mechanical mixing. It is possible that increased friction was responsible for the mixing. Alternatively, vertical wind shear may have also played a role. In either case, the stronger winds above the planetary boundary layer were mixed down to the surface and we observed sustained winds to 54 m.p.h. with gusts to 75 m.p.h. in Columbus.


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