87th AMS Annual Meeting

Wednesday, 17 January 2007
Impacts of recurving West Pacific tropical cyclones on extratropical predictability in the Northern Hemisphere
Exhibit Hall C (Henry B. Gonzalez Convention Center)
Heather M. Archambault, University at Albany/SUNY, Albany, NY; and D. Keyser and L. Bosart
Interactions between recurving West Pacific tropical cyclones (TCs) and the extratropical large-scale flow regime can yield major downstream circulation changes and potentially result in significant forecasting problems over the Pacific Ocean and North America. The purpose of this presentation is to discuss the influence of recurving West Pacific TCs on Northern Hemispheric (NH) extratropical predictability over an approximately twenty-two month period (1 September 2004 to 20 June 2006) from statistical and synoptic perspectives. This talk will consist of two parts: i) a statistical analysis of extratropical NH predictability during periods of West Pacific TC recurvature, and ii) a case study of the impact of a recurving West Pacific TC on the generation of a Rossby wave train associated with a reduction in extratropical NH predictability.

To examine predictability during periods of West Pacific TC recurvature, a dataset of 500-hPa geopotential height anomaly correlations of National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) model forecasts is analyzed. This dataset contains four-times-daily (0000, 0600, 1200, and 1800 UTC) NH 500-hPa geopotential height anomaly correlations between 20N and 80N for wavenumbers 13, 49, 1020, and 120. The dataset used in the case study to discern the dynamical impacts of a recurving West Pacific TC on the formation of a Rossby wave train is the four-times-daily 1.0 x 1.0 NCEP GFS analysis.

Statistical results will show that instances of recurving West Pacific TCs can be linked to reduced extratropical predictability in the NH identified by periods of below-average GFS forecast skill. In addition, a case study illustrating the crucial role of recurving TC Haima in the West Pacific initiation of a potent NH Rossby wave train associated with reduced GFS forecast skill will be discussed from a potential vorticity perspective.

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