Irma and Hermine: Two storms with different impacts

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By: Charles Roop | WCTV Eyewitness News
September 15, 2017

TALLAHASSEE, Fla. (WCTV) -- In just over a year, the Big Bend and South Georgia encountered two tropical systems.

Hermine made a direct landfall from the gulf while Irma crawled through the peninsula of Florida. But there were other differences between these two storms?

Hermine had the highest surge because of the direction it came from. The storm moved through the gulf, allowing that southerly flow around the center of circulation. This funneled plenty of water through the gulf into the Big Bend. Surge totals in Cedar Key totaled 7.5 feet above mean tide levels.

With Irma, the storm's center was farther east. This had the opposite effect with surge; water actually "disappeared" from many gulf coastal areas in the Big Bend down to Tampa Bay. Preliminary data from Cedar Key had a tide deficit of 7.69 feet. The water did come back, any only caused the water in Cedar Key to reach nearly three feet above normal tide levels.

Hermine brought plenty of rainfall in our area. Tallahassee picked up 7.64 inches, according to the National Hurricane Center's final report on the hurricane. Tallahassee picked up 5.48 inches, and Apalachicola had 3.40 inches of rain in the official rain bucket.

With Irma, it was much less as the storm began to deteriorate as it was influenced by wind shear from the trough in the Southeast U.S. and the lack of fuel from the ocean. This caused the rain and wind field to spread away from the center of circulation. Our western areas didn't pick up much, as Apalachicola only got 0.61 inches of rain on Monday. Tallahassee got a bit more rain with 1.34 inches. Valdosta's daily report from the National Weather Service showed missing data. It's likely the station took a hit from Irma.

Hermine recorded some gusts of tropical storm force in the Big Bend, but none were hurricane force. The NHC noted in their final report that the sparse observation network could have missed recording hurricane-force winds. It's likely the highest winds were on the eastern eye wall, which went over Jefferson County after landfall.

The WeatherSTEM station at FSU, though elevated, recorded a 64-mph gust. Tallahassee picked up a gust of 44 mph before Hermine took the station out. Apalachicola received a gust of 53 mph.

The highest winds recorded in our area were gusts at Moody Air Force Base of 62 mph, with 56 mph recorded down the road in Valdosta. Tallahassee International Airport received a gust of 55 mph. Apalachicola got a gust of 48 mph.

Hermine's pattern was a bit different than Irma's. The same Bermuda high played an important role a year ago as the ridge kept the storm south between Cuba and Florida as a weak wave and then Tropical Depression. It become Tropical Storm Hermine on Aug. 31, then started to turn more northward around the western edge of that high. Once it left the shear, it was able to intensify as it moved northward, then northeastward. Hermine made landfall on Sept. 2 at 1:30 a.m., near St. Marks.

With Irma, it rode along the southwestern edge of the high until it caught a weakness, and moved northward. This time, a developing upper-level trough in the Southeast helped not only to lift it northward as the storm rode between the ridge and trough, but to tear the storm apart. Tropical systems do not like wind shear; therefore, the storm was torn apart as it went northward through the Florida peninsula. Based on upper-air observations, the storm quickly became more cold core by time the center arrived in the Big Bend. The convection and strongest winds began to move away from the center.

Looking at the impacts and characteristics between the two storms, they prove that no two storms are alike.