Date of Award

8-1-2021

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (xxii, 127 pages) : color illustrations. color maps.

Dissertation/Thesis Chair

Kristen L. Corbosiero

Keywords

Emergency managers, Intensity, Probabilistic graphics, Size, TC-trough interactions, Tropical cyclones, Cyclone forecasting, Cyclones, Emergency management, Communication in meteorology

Subject Categories

Atmospheric Sciences | Communication

Abstract

The severity of tropical cyclone (TC) hazards is modulated by both TC intensity and size. More intense TCs produce stronger storm surges and increase wind damage. Larger TCs potentially impact more people, increase the duration of TC hazards, produce stronger storm surges and increase the amount of rainfall and flooding. Thus, accurately forecasting both TC intensity and size and effectively communicating those forecasts are critical to properly preparing communities for TC impacts. Forecast accuracy can be improved by enhancing our understanding about the processes that cause changes in TC intensity and size. This research divides the Extended Best Track dataset into four groups based on 12- and 24-h changes in TC intensity and size: Increasing in Intensity and Size (AllI), Increasing in Intensity and Decreasing in Size (IIandDS), Decreasing in Intensity and Increasing in Size (DIandIS) and Decreasing in Intensity and Size (AllD). Atmospheric reanalyses of surface latent heat flux from the 5th Generation of the European Centre for Medium-range Weather Forecasts (ERA-5) and infrared (IR) brightness temperatures from Gridded Satellite (GridSat) dataset are composited for each group. Composites of surface latent heat fluxes for AllI and AllD TCs match results from prior literature; however, the pattern breaks down for IIandDS and DIandIS TCs. IIandDS TCs have increases in surface latent heat fluxes that extended outward downshear left, where reductions in surface latent heat fluxes are expected according to Shen et al. (2021). This result aligns, however, with the finding from Chen et al. (2018) that intensifying TCs are associated with positive surface latent heat flux anomalies downshear. DIandIS TCs have decreases in surface latent heat fluxes that extend outward right of shear, where increases in surface latent heat fluxes are expected. Composites of IR brightness temperatures for DIandIS TCs show a large swath of cooling cloud tops downshear and downshear left that do not coincide with increases in surface latent heat fluxes. Analysis of individual cases show that DIandIS TCs are often interacting with upper-level troughs and nearing extratropical transition. These synoptic interactions may modulate changes in TC intensity and size apart from those expected from surface latent heat fluxes. A TC’s diurnal pulse may also play a slight role in driving intensity and size changes of AllI and AllD TCs. Effectively communicating a forecast is just as essential as being accurate. Emergency managers (EMs) are a key partner in preparing communities for TC hazards. This research also used data from a survey of EMs conducted in 2020 by the National Institute for Risk and Resilience to understand EMs’ knowledge about the influence of size on TC hazards and the importance of TC size for evacuation decisions. Results from the survey analysis demonstrate that size is among the least likely to be selected by EMs as a factor affecting storm surge and rainfall amount. A majority of EMs do, however, correctly identify TC size as a factor. EMs with experience making or helping to make evacuation decisions also indicate that TC size is an important factor in decision-making. In addition, rainfall amount – a TC hazard impacted by size – appears to be especially poorly communicated by the current probabilistic graphic. EMs are the most confident that they can interpret all the information provided in this graphic, and many indicate that they are likely to use it to understand and communicate the risk. However, the majority incorrectly interpret the graphic.

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