Large-Scale Characteristics and Probability of Rapidly Intensifying Tropical Cyclones in the Western North Pacific Basin

Abstract

The China Meteorological Administration (CMA) and the National Centers for Environmental Prediction (NCEP) reanalysis datasets are employed to examine the large-scale characteristics of rapidly intensifying western North Pacific tropical cyclones (TCs). The results show that of all 27 581 samples for the period 1970–2007, 85%, 65%, and 47% of all tropical depressions (TDs), tropical storms (TSs), and typhoons (TYs), respectively, intensify. Of the 1214 TCs, 18%, 70%, 30%, and 10% of all tropical cyclones, supertyphoons, severe typhoons, and typhoons, respectively, underwent rapid intensification (RI) at least once during their lifetime. Three kinds of cases—RI, slow change in intensity (SC), and rapid decay (RD)—during the period 1982–2007 are used to analyze the large-scale conditions associated with them. The comparison shows that the RI cases tend to occur farther south and east than the non-RI cases. In addition, the RI cases have a more westerly component of motion and intensify more during the preceding 12 h than do the non-RI cases. For the non-RI cases, the SC cases tend to have a lower initial intensity and a lower speed of motion than do the RD cases. Also, the RI cases are farther from their maximum potential intensity and develop in warmer water, lower vertical shear, and more easterly upper-tropospheric flow than do the non-RI cases. The probability of RI for TCs is estimated by using the rapid intensify index (RII) developed in this study for the western North Pacific basin. The verification based upon the cross validation shows that the RII is skillful relative to climatology.

Multidecadal Variability of Tropical Cyclone Rapid Intensification in the Western North Pacific

“…Ventham and Wang (2007) found that in the WNP, RI is characterized by lower-level monsoon confluence environmental flows, which play critical roles in determining RI. Shu et al (2012) examined the effects of large-scale environmental factors on TC RI in the WNP. It was found that the RI cases have higher lower-tropospheric relative humidity (RHUM), lower VWS, and more easterly uppertropospheric flow than the non-RI cases.…”

“…) per 24 h is employed to define RI events since it represents the nearly 95th percentile of the intensity changes in 24 h in the WNP (Wang and Zhou 2008;Shu et al 2012).…”

Modeling Rapid Intensification of Typhoon Saomai (2006) with the Weather Research and Forecasting Model and Sensitivity to Cloud Microphysical Parameterizations

“…Especially, rapid intensification (RI) is one of the most challenging and the least well understood problems in tropical cyclone prediction today. Furthermore, the most intense TCs in the Northern Hemisphere often have a RI period during the peak season, and account for nearly three-quarters of all the RI events (Frederick 2003;Kaplan and DeMaria 2003;Ventham and Wang 2007;Shu et al 2012). RI also poses a significant threat to ships and a growing number of coastal communities.…”

Environmental influences on the intensity changes of tropical cyclones over the western North Pacific

“…1). A recent study by Shu et al (2012) also showed that the intensifying events usually have more easterly upper-tropospheric flow than the nonintensifying events, suggesting a possible role of the WNPSH for the former. Since whether and how the WNPSH influences TC intensity has not been obtained, the potential impacts of environmental parameters associated with the WNPSH were not taken into account in developing MPI in Zeng et al (2007).…”