Evolutionary periods of precipitation distribution in tropical cyclones (TCs) are sometimes misrepresented in numerical weather prediction models due to the rapid nature of TC structure changes that accompany intensity change. To better understand quantitative changes in TC rainband structure around landfall, I quantify the spatial distribution of precipitation in 62 landfalling TCs along the Gulf of Mexico and Atlantic coasts of the U.S. between 1998 and 2014. The Tropical Rainfall Measuring Mission (TRMM) 3B42 product is utilized to assess three spatial measures of precipitation: 1) area, 2) closure, and 3) dispersion. Calculations are made using two rain rate thresholds, 0.254mm/hr and 5mm/hr, to capture and compare changes in light and heavy precipitation, respectively. Changes in TC precipitation are statistically different based on landfall location along the Atlantic vs. Gulf. Overall, dispersion (measure of centrality) is the most dissimilar metric due to variability between 0.254mm/hr and 5mm/hr results. Lighter precipitation decreases in area and expands away from the TC center, while heavier precipitation contracts rather than disperses in Gulf landfalling storms. A k-means clustering produces six landfall regions and reinforces the result of heavier precipitation becoming more central along the Gulf, while Atlantic landfalling storms exhibit decreased centrality. Significant differences were not found in storms that undergo extratropical transition or dissipate later in lifecycle. The holistic approach exhibited by this study reveals wide variability among a large dataset of storms making landfall; therefore, sub-setting techniques are helpful to hurricane forecasters in understanding the role of landfall location. / MS / As our coastal communities become progressively vulnerable due to increased urbanization and settlement along United States coastlines, natural disasters, such as flooding caused by hurricanes and nor’easters, will continue to cripple coastal populations. Strong winds, storm surge, and heavy rains upon landfall during tropical cyclones produce billions of dollars’ worth of damage to infrastructure and natural resources. By understanding structural changes of hurricanes in terms of the spatial coverage of rainbands before, during, and just after landfall, operational meteorologists will be better equipped to aid in public preparedness and provide improved rainfall forecasts to emergency management personnel. This research examines the structural changes in precipitation as hurricanes make landfall along the Gulf of Mexico and Atlantic coasts of the U.S. using three shape metrics; 1) area (2-D coverage), 2) closure (proportion around storm center), and 3) dispersion (spread away from storm center). Precipitation is subset into light (0.254 mmhr⁻¹ ) and heavy (5 mmhr⁻¹ ) rain rates in order to capture and compare the structural changes of 62 landfalling hurricanes between 1998 and 2014. I find that the average precipitation distributions of Gulf and Atlantic landfalling hurricanes at the time of landfall are similar; however, there are important changes in these distribution based on landfall location. Specifically, Gulf storms become larger and heavy rain contracts around the TC center, while Atlantic storms become asymmetric and spread out through landfall. These results demonstrate the importance of landfall location and the role that environmental factors may play in determining how hazards related to flooding can evolve along the U.S. coastline.

The thesis is presented in alternative format, meaning that the results of the thesis take the form of three journal articles, each telling a distinct story within the subject matter, but collectively highlighting the sensitivity of bands to frictional and diabatic processes. Paper 1 is an idealised-modelling study with the Weather Research and Forecasting (WRF) model, in which moist baroclinic waves are simulated from an initial zonally uniform mid-latitude jet on an f-plane at 20-km grid spacing, and the sensitivity of the resulting precipitation bands is explored. Paper 2 employs further WRF idealised-baroclinic-wave simulations and takes a simulation from Paper 1, after the cold front has formed, as the initial condition. A nested domain at 4-km grid spacing is inserted when this simulation is re-initialised to invesigate the sensitivity of finer-scale precipitation cores along the surface cold front. In both Papers 1 and 2, friction and latent-heat release enhance multiple banding at the two distinct horizontal scales, while surface fluxes hinder multiple banding. Paper 3 studies post-frontal snowbands over the English Channel and Irish Sea during extreme cold-air outbreaks in the winters of 2009-10 and 2010-11, via a climatology of precipitation-radar, sounding, and SST data, and real-data WRF sensitivity simulations of one such band over the English Channel. The observational and modelling results show that strong winds and large differential heat fluxes between land and sea were necessary to generate banded precipitation. Coastal orography and the land-sea frictional contrast aided the morphology of bands, but banded precipitation did still form in the absence of these influences in the sensitivity simulations. These three studies and the thesis as a whole highlight the role of frictional and diabatic processes in modifying various types of precipitation bands within baroclinic waves, and in generating bands that would otherwise not exist.