Anomalous tropical cyclone activity in the northwestern Pacific in 2014

Abstract:

Northwestern Pacific experienced anomalous tropical cyclone activity in July and August 2014. It is the first time since 1949 that no tropical cyclones forms in the northwestern Pacific in August, a peak tropical cyclone month in climatology. There are only 4 tropical cyclones occurred in July of 2014, among which 3 are super typhoons. Such high percentage of super typhoons is also uncommon since 1949. The anomalous tropical cyclone activity occurred in the background of decreasing eastern Asian summer monsoon (EASM) since the end of 1970s and negative Pacific Decadal Oscillation (PDO) phase since 2006 with possible phase transition from negative to positive in 2014. Intraseasonal Oscillation (ISO) also plays a significant role in inhibiting the tropical cyclone genesis in August of 2014 by preventing warm and moist air into northwestern Pacific. We are unable to confirm or reject the role of climate change in the July and August anomalous tropical cyclone activities due to the inability of CIMP5 models to accurately simulate the 850hPa wind anomaly. The CMIP5 does not show any obvious trend during 1948-2014, while reanalysis data shows significant increasing trend of low level easterly. The inability of CMIP5 in simulating 850hPa wind might be related to their limited performance in reproducing the EASM, transition of PDO and the propagation of ISO.