Inland Tropical Cyclone Intensity Decay in the Continental United States

Tropical cyclone (TC) hazard preparation is mostly focused on coastal cities with less attention typically paid to inland regions. The impact of TCs that propagate far inland is often underestimated and can cause unexpected loss of life and economic loss. This dissertation aims to understand the decay process of TCs during the post-landfall stage by answering three main research questions: (1) What are the general patterns of inland tropical cyclones, including spatial variations, decay rates, and translation speeds? (2) Are there temporal changes in the intensity decay from inland moving hurricanes? (3) How is the hurricane post-landfall dissipation related to its nearshore intensity? These three research questions establish the framework of this dissertation and reflect three essential aspects of geographical distribution, temporal variation, and implications of risk preparations. To answer the first research question, Chapter Two examines TC decay patterns for different continental U.S. regions based on historical storm landfall events. I find that inland moving hurricanes over the Gulf Coast decay faster within the first 24 hours after landfall than those over the Atlantic East Coast. By comparison, historical hurricanes transiting the Florida peninsula maintained, on average, more than 80% of their landfall intensity when transiting across the state. To explore the temporal changes of hurricane inland wind decay, Chapter Three introduces the decay period as a new metric to measure the time required for a landfalling hurricane to decay from hurricane intensity to below tropical storm intensity. Landfalling hurricanes over the U.S. have decayed slower since the 1980s, potentially correlated with long-term climate variability. The potential relationship between post-continental U.S. landfall hurricane dissipation and nearshore hurricane conditions is investigated in Chapter Four. Hurricanes that underwent intensification before landfall are more likely to weaken at a slower rate after landfall. This relationship is not consistent along the Gulf Coast, possibly due to variations in surface conditions. Southeastern Florida is identified as an area under especially high risk due to a combination of frequent intensification prior to landfall, high landfalling wind speeds, and weak dissipation rates after landfall. The three aspects investigated in this dissertation not only enrich the current knowledge base for inland TC behavior but, more importantly, address the potential impacts of the changing climate on inland tropical cyclones. This area has not received significant attention from the research community despite its potential critical impacts. The framework of this research could also be applied to other cyclone-prone regions worldwide, giving guidance for inland regions to adapt to TC risks in a warming climate