Anticipating Transitioning Tropical Storm Impacts in the Northeast

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Extratropical transition, tropical cyclones, extratropical characteristics, northeastern United States
Tougas, Trent
ABSTRACT Anticipating Transitioning Tropical Storm impacts in the Northeastern United States by Trent N. Tougas Plymouth State University, May, 2022 Extratropical transition is a process which is known to occur as tropical cyclones move poleward over cooler sea surface temperatures and interact with the midlatitude westerlies. Once a tropical cyclone begins to interact with the cooler ocean temperatures and the midlatitude westerlies, they begin to take on extratropical characteristics which can pose many operational forecasting challenges. The purpose of this research is to anticipate transitioning tropical storm impacts in the northeastern United States and improve forecasts up to three days before impact. To fully analyze and understand the atmospheric features that are important in anticipating tropical cyclones impacts, cyclone phase space diagrams, synoptic composite and anomaly charts were developed. Each tropical cyclone in the cyclone phase space archive from the year 2000- present were evaluated to see if these cyclones were fit for use in this study. To qualify for this study a tropical cyclone must: recurve in the Atlantic, fully undergo extratropical transition on the phase space diagram, and the impacts that the cyclone produced after undergoing extratropical transition occurred in the forecasting region of the NWS Gray, Maine CWA office. A total of 13 storms met the criteria. Iowa State Mesonet and the National Storm Prediction Center archives were utilized to create an impact report for each tropical cyclone that was included in the study. After the storm impacts were recorded, the tropical cyclones were categorized based on what impacts they produced. The two categories created were Wind & Rain events, and Rain events. Once the impact categories were created, synoptic composite and anomaly charts, and cyclone phase space diagrams were created to try and understand the different atmospheric phenomena at play in creating the different impacts produced from different tropical cyclones undergoing extratropical transition in the northeast. The primary features responsible for Wind and Rain vs Rain only impacts include: 1) system strength, 2) symmetry and warm core depth, 3) system track, 4) location of the trough at 500mb and 5) jet streak strength and location at 250mb. In addition to the conclusion made from this research, an atmospheric ingredients checklist was created for the operational forecasters at the forecast office of NWS Gray, Maine to help forecasting impacts that cyclones undergoing ET will produce in the northeastern United States.