A comparison of typhoon best-track data in the western North Pacific: irreconcilable differences

The SST has gone up in all of the ocean basins by approximately 0.5° C over the past several decades. During the prolific 2005 hurricane season in the North Atlantic, the SST across much of tropics of that basin was at an all-time historical high. In a recent paper, Webster et al. (2005) claim that there are already observed increases in the number of very intense tropical cyclones in most of the global TC basins. The release of W2005 caused an immediate firestorm in the tropical cyclone community. Some of the TC data sets do indeed show an increase in the proportion among all TCs of CAT 4 and CAT 5 cyclones. The strongest rebuttal to the findings of W2005 came from the community of those researchers and forecasters familiar with the methods by which the TC best track data sets were created, or directly involved with TC reanalysis efforts. Such individuals generally claim that tropical cyclone best track data sets are of insufficient quality to derive meaningful information on secular trends, or that they possess inherent biases so as to negate the statistical significance of the findings of W2005. In this presentation, the focus will be the TC record of the western North Pacific. It will be shown that the best track data sets of the two primary agencies responsible for basin-wide TC coverage — the Joint Typhoon Warning Center (JTWC) and the Japan Meteorological Agency (JMA) — are so incompatible as to call into question the utility of this data for climate studies. Many have suggested adjustments be made for the procedural differences between these two agencies so as to reconcile the discrepancies in their best-track data (e.g., one-minute VS ten-minute wind averages and different conversions for Dvorak “T” numbers). It is the thesis of this presentation that this effort will prove to be futile. These agency's typhoon best-track data sets have irreconcilable differences. The creation of an independent typhoon best-track data set with uniform standards for identifying TCs and TC intensity (e.g., Kossin 2007) may be the only way to uncover any changes in western North Pacific tropical cyclone climate.