New model used to keep a better 'eye' on storms

By Dave

CHARLESTON, S.C. (WCIV) -- Forecasting hurricanes is difficult, especially with respect to the intensity of a storm. Enormous strides have been made in forecasting the eventual path of tropical systems, but still to this day it remains difficult to predict how strong a storm will get.

In 2012, NOAA started using a new computer model to help predict the start of what is known as the "eyewall replacement cycle," a key indicator that a storm's strength and size is about to change. The new tool will help NOAA forecasters provide valuable information to emergency managers about an evolving hurricane.

The eyewall is an organized band of clouds that immediately surround the center, or eye, of a hurricane. The most intense winds and rainfall occur near the eyewall. This is the part of a storm which generates surge, and typically causes the most damage.

Within a hurricane, eyewall replacement cycles occur when a second concentric eyewall forms around the original and eventually overtakes it. This phenomenon especially happens in strong, long-lived hurricanes, category three and higher.

"Hurricanes usually strengthen and grow gradually over time, but eyewall replacement cycles can cause very sudden changes in size and intensity," said Jim Kossin, a scientist with NOAA's National Climatic Data Center, who led the effort to create the model.

The model attempts to predict the start of the developing eyewall replacement cycle by measuring certain variables of the storm's structure and surrounding environment, and relating these to the conditions observed during past replacement cycles. Kossin said skillful forecasting of these natural cycles is crucial to protecting life and property.

"As it was approaching New Orleans, Hurricane Katrina weakened but grew in size because of an eyewall replacement cycle. The huge wind field led to an enormous storm surge that devastated the Gulf Coast," Kossin said.

The model uses data from NOAA's Geostationary Operational Environmental Satellites (GOES) to identify hurricane structure patterns related to eyewall replacement cycles. Microwave images from NOAA's polar orbiting satellites were also added extensively to create the model using past data.

"This is an important first step towards understanding how we can use the eyewall cycle to someday improve intensity forecasts," said James Franklin, branch chief of the hurricane specialist unit at the National Hurricane Center.

* Dave Williams received a B.S. in atmospheric science from The Ohio State University. Before joining ABC News 4, Dave was just up the road at WBTW in Myrtle Beach. Armed with a wealth of experience forecasting the weather in the Palmetto State, Dave is a member of the National Weather Association, American Meteorological Society, and holds a Seal of Approval from the NWA.