Predicting Intensity Changes Subsequent to Concentric Eyewall Events
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Date
2014-02
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Abstract
Concentric eyewall events have been documented in very intense tropical cyclones with increasing frequency in the last two decades. During a concentric eyewall event, an outer (secondary) eyewall forms around the inner (primary) eyewall. Substantial structural changes usually follow: both eyewalls may survive or dissipate, or only one eyewall may survive. Improved instrumentation on aircraft and satellites greatly increases the likelihood of detecting an event. However, forecasting intensity during and after these events remains challenging. When concentric eyewall events occur near the time of landfall, the increased uncertainty in short-term intensity engenders even greater challenges to emergency preparations.
A sixteen-year (1997-2012) database of concentric eyewall events is developed by analyzing various sources. Included sources are published documents and microwave satellite imagery. Events are identified in both the North Atlantic (41 events in 25 tropical cyclones) and eastern North Pacific (17 events in 14 tropical cyclones) Oceans. About half of North Atlantic major hurricanes (winds of 100 kt or greater) form concentric eyewalls at some point during their lifetime, and about one-quarter of eastern North Pacific major hurricanes form concentric eyewalls. Climatological characteristics (location and time of year) are analyzed. Concentric eyewalls tend to occur in the southern portion of the regions; this distribution is especially apparent for cases of systems forming concentric eyewalls multiple times.
The intensity change subsequent to the concentric eyewall event (weakening, no change, or strengthening) is identified from the Best Track data. About 25% of tropical cyclones with concentric eyewalls are stronger than at the time of formation at 12 h, 24 h, and 36 h following formation in both regions. Roughly 50% of North Atlantic concentric eyewall cases are weaker at 12 h, 24 h, and 36 h following formation. In the eastern North Pacific, 76% of cases were followed by weakening at 36 h. Of the 25 North Atlantic tropical cyclones which developed concentric eyewalls, 10 made landfall within 36 h of developing concentric eyewalls.
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Mathematical and Physical Sciences: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)
Keywords
tropical cyclone, hurricane, concentric eyewall, satellite observations, intensity forecasting