A conceptual model for the influence of TUTT cells on tropical cyclone motion in the northwest Pacific Ocean

Abstract

Eleven (10 Pacific, 1 Atlantic) tropical cyclones (TCs), which include typhoons/hurricanes and tropical storms, are examined using the latest 40-yr ECMWF Re-Analysis (ERA-40) dataset and Joint Typhoon Warning Center (JTWC) best-track data to determine if and how tropical upper-tropospheric trough (TUTT) cells influence TC tracks. This type of interaction has led to rather large TC track forecast errors at 72 h (2000 + km) in the northwest Pacific and is often ignored or poorly forecast due to inadequate numerical model TUTT cell predictions. Ten selected cases out of the initial 25 potential Pacific cases exhibited a "nonstandard" TC track; a TUTT cell was the sole large-scale transient feature within 2000 km of the TC's center, and the TC intensity was >17 m s-1. The circulations' separation distance, orientation, intensity, and TUTT cell's closed circulation size are critical characteristics in determining the likelihood of a TUTT cell influencing a TC track. Interactions occur at distances greater than 1700 km, continue for periods from 24 to 48 h, and occur 2-3 times per year in the NW Pacific. Examination of the TC's tropospheric winds' deep layer mean (100-1000 hPa), and upper (100-500 hPa), middle (300-850 hPa), and lower (500-1000 hPa) layers, along with various quadrants of the upper layer, demonstrate a link between the TUTT cell's wind field and the nonstandard TC tracks.Aconceptual model of how a TUTT cell can influence TC track is presented. The model provides decision-grade operational guidance for TC forecasters using pattern recognition scenarios. Application of the conceptual model at the JTWC is currently under way. © 2009 American Meteorological Society.