Objective Identification of Annular Hurricanes

Abstract

Annular hurricanes are a subset of intense tropical cyclones that have been shown in previous work to be significantly stronger, to maintain their peak intensities longer, and to weaken more slowly than average tropical cyclones. Because of these characteristics, they represent a significant forecasting challenge. This paper updates the list of annular hurricanes to encompass the years 1995-2006 in both the North Atlantic and eastern-central North Pacific tropical cyclone basins. Because annular hurricanes have a unique appearance in infrared satellite imagery, and form in a specific set of environmental conditions, an objective real-time method of identifying these hurricanes is developed. However, since the occurrence of annular hurricanes is rare (ϳ4% of all hurricanes), a special algorithm to detect annular hurricanes is developed that employs two steps to identify the candidates: 1) prescreening the data and 2) applying a linear discriminant analysis. This algorithm is trained using a dependent dataset (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) that includes 11 annular hurricanes. The resulting algorithm is then independently tested using datasets from the years 2004-06, which contained an additional three annular hurricanes. Results indicate that the algorithm is able to discriminate annular hurricanes from tropical cyclones with intensities greater than 84 kt (43.2 m s Ϫ1). The probability of detection or hit rate produced by this scheme is shown to be ϳ96% with a false alarm rate of ϳ6%, based on 1363 six-hour time periods with a tropical cyclone with an intensity greater than 84 kt (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006).

Structure and Formation of an Annular Hurricane Simulated in a Fully Compressible, Nonhydrostatic Model—TCM4*

“…The environmental conditions favorable for the formation of annular hurricanes that KKD03 identified are all met in our model simulation (except for a slightly higher SST in this study). Knaff et al (2008) recently show that only about 9% of the hurricanes that met environmental conditions eventually developed into annular hurricanes in the Atlantic during 2004-06. This indicates that annular hurricanes are, indeed, rare events and must form with both very strict environmental conditions and internal storm dynamics.…”

From concentric eyewall to annular hurricane: A numerical study with the cloud‐resolved WRF model

“…The primary reason for the slow improvement is associated with the difficulties in discerning and simulating the details of storm inner core. Recently, particular attentions have been focused on the formation of concentric eyewalls and annular hurricanes (AH) due to their distinctive features and close connections with hurricane intensity [ Houze et al , 2007; Knaff et al , 2003, 2008].…”

“…For instance, the annular hurricane Daniel (2006) over the Eastern Pacific started out with a small eye (http://www.nrlmry.navy.mil/tc_pages/tc_home.html). It presents prominent annular structures after the concentric eyewall replacement [ Knaff et al , 2008]. However, the detailed transformation processes have not been understood.…”

A Systematic Classification Investigation of Rapid Intensification of Atlantic Tropical Cyclones with the SHIPS Database

“…In addition to case studies, composite analysis is another major methodology for identifying common factors affecting TC intensity changes and for understanding the underlying physics (e.g., Hanley et al 2001;Knaff et al 2004Knaff et al , 2008Zehr and Knaff 2007;Camargo et al 2007;Ventham and Wang 2007;Hendricks, et al 2010;Sanabia et al 2014). Ventham and Wang (2007) also suggested that composite analysis may help to derive new predictors for RI.…”