Improved Tropical Cyclone Intensity and Intensity Spread Prediction in Bifurcation Situations

다국어 초록 (Multilingual Abstract)

Bifurcation or bi-modal tropical cyclone intensity forecastsmay arise due to uncertainty in the timing of formation, timing andmagnitude of rapid intensification periods, or track forecast uncertaintyleading to landfall or non-landfall or leading to interactionwith warm- or cold-ocean eddies. An objective technique isdeveloped and tested to detect these intensity bifurcation situations inour weighted-analog intensity (WANI) forecasts that are based on the10 best historical analogs to the Joint Typhoon Warning Center(JTWC) official track forecasts. About 19% of the overall sample of1136 WANI forecasts in the western North Pacific during the 2010-2012 seasons met the criteria for a substantial intensity bifurcationsituation. Using a hierarchical clustering technique, two clusters ofthe 10 best analogs are defined and separate WANI forecasts andintensity spreads are calculated for the two clusters. If an alwaysperfect selection of the correct cluster WANI forecast of eachbifurcation situation is made, a substantial improvement in theintensity mean absolute errors is achieved relative to the originalWANI forecasts based on all 10 of the best analogs. These perfectclusterselection WANI forecasts have smaller bias errors and aremore highly correlated with the verifying intensities at all forecastintervals through 120 h. Without further bias correction and calibration,the cluster WANI intensity spreads are under-determined asthe Probability of Detections are smaller than the desired 68%. Fourexamples of WANI cluster predictions of intensity bifurcationsituations are provided to illustrate how a correct choice of the intensityforecast and the intensity spread can be the basis for improvedwarnings of the threat from western North Pacific tropical cyclones.

참고문헌 (Reference)

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