| Eleven tropical cyclones (TCs) are examined using the latest ECMWF reanalysis (ERA-40) and JTWC best track data to determine how tropical upper tropospheric trough (TUTT) cells influence TC tracks. This type of interaction has led to enormous TC track forecast errors at 72 hour (2000+ km) in the northwest Pacific and are often overlooked and under-forecast frequently due to poor numerical model TUTT cell forecasts. Cases are selected because a TC exhibited a "non-standard" 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. Analysis shows that the circulations' separation distance, orientation, intensity, and the depth and breadth of the TUTT cell's closed circulation are critical characteristics in determining the likelihood of a TUTT cell influencing a TC's track. Interactions occur at distances greater than 1700 km, continue for periods ranging from 24 to 48 hours and happen 2-3 times per year in this active TC basin.Examination of the TC's deep layer mean (DLM), upper, middle and lower layers along with various quadrants of the upper layer (100-500 hPa) demonstrate a link between the TUTT cell's wind field and the non-standard TC tracks. The TC's 5°-7° mass-weighted DLM steering environment is found to be closest to actual TC motion in most cases. TC intensity variations and circulation proximity sometimes results in the DLM's 3°-5° radial band being closer to actual TC motion.A conceptual model of how a TUTT cell can influence TC track is presented. The model provides quantified, decision-grade operational guidance for TC forecasters using pattern recognition scenarios. Application of the conceptual model at the JTWC is currently underway. |
