Description
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.
