Developing versus Nondeveloping Disturbances for Tropical Cyclone Formation. Part II: Western North Pacific

Abstract

Global daily reanalysis fields from the Navy Operational Global Atmospheric Prediction System (NOGAPS) are used to analyze Northern Hemisphere summertime (June-September) developing and nondeveloping disturbances for tropical cyclone (TC) formation from 2003 to 2008. This is Part II of the study focusing on the western North Pacific (WNP), following Part I for the North Atlantic (NATL) basin. Tropical cyclone genesis in the WNP shows different characteristics from that in the NATL in both large-scale environmental conditions and prestorm disturbances.A box difference index (BDI) is used to identify parameters in differentiating between the developing and nondeveloping disturbances. In order of importance, they are 1) 800-hPa maximum relative vorticity, 2) rain rate, 3) vertically averaged horizontal shear, 4) vertically averaged divergence, 5) 925-400-hPa water vapor content, 6) SST, and 7) translational speed. The study indicates that dynamic variables are more important in TC genesis in the WNP, while in Part I of the study the thermodynamic variables are identified as more important in the NATL. The characteristic differences between the WNP and the NATL are compared.

The Effect of Water Vapor on Tropical Cyclone Genesis: A Numerical Experiment of a Non-Developing Disturbance Observed in PALAU2010

“…McBride and Zehr (1981) concluded that vertical shear is substantially strong even in developing cases over the western North Pacific. Fu et al (2012) also found that a difference in the strength of vertical shear was small between developing cases and non-developing cases over the Fig. 4.…”

“…The vortical hot tower is mainly a low-level convective scale vortex and is suggested as a possible embryo for the organization of a TC vortex (Hendricks et al 2004;Houze et al 2009;Montgomery et al 2006). However, such mesoscale vortices are also found in disturbances that do not develop into a TC (a non-developing disturbance) (Fu et al 2012;McBride and Zehr 1981;Zehr 1992).…”

“…Fu et al (2012) showed the differences in environmental conditions between developing disturbances and non-developing disturbances over the western North Pacific. Larger meridional gradients of zonal wind and low-level convergences are found in developing disturbances.…”

Precursor synoptic‐scale disturbances associated with tropical cyclogenesis in the South China Sea during 2000–2011

“…In this study, we examined only developing disturbances. A comparison of developing and non-developing disturbances such as observational studies done by Peng et al (2012) and Fu et al (2012) is needed, in order to fully understand cyclogenesis processes over the SCS.…”

Observations of a Nondeveloping Tropical Disturbance in the Western North Pacific during TCS-08 (2008)

“…Only a small fraction of all tropical disturbances that occur over tropical ocean basins develop into tropical cyclones (Gray 1982;Lee 1989;Simpson et al 1997;Fu et al 2012). Gray (1998, 37-38) commented that to adequately understand the process of tropical cyclogenesis we must ''thoroughly document the physical differences between those systems which develop into tropical cyclones from those prominent tropical disturbances which have a favorable climatological and synoptic environment, look very much like they will develop but still do not.''…”