Skill of Western North Pacific Tropical Cyclone Intensity Forecast Guidance Relative to Weighted-Analog Technique

Hsiao-Chung Tsai,Russell L. Elsberry 한국기상학회 2016 Asia-Pacific Journal of Atmospheric Sciences Vol.52 No.3

The accuracy of the western North Pacific tropical cyclone intensity forecast guidance products available at the Joint Typhoon Warning Center (JTWC) is evaluated relative to a new skill metric called Weighted Analog Intensity Pacific (WAIP) that includes knowledge of the JTWC official track forecast and the current intensity, which is information that is available at the time the intensity forecast is generated. An intensity consensus technique called S5XX that includes statistical-dynamic intensity forecasts plus other dynamic and thermodynamic prediction techniques has statistically significant smaller errors than WAIP at 24 h and 48 h and has similar accuracy through 120 h. While the track consensus CONW is a critical input to the JTWC official track forecast, it has no skill relative to WAIP as an intensity forecast. Three regional numerical models also have no skill relative to WAIP, and especially at forecast intervals beyond 72 h because their mean absolute errors are statistically significantly larger than for WAIP. Furthermore, these regional models have statistically significant positive or negative intensity biases relative to the verifying intensities. However, an experimental consensus technique called CMES that includes these three regional models has small accuracy relative to WAIP in the 24 h to 72 h forecast intervals. Geographical-based comparisons of the intensity guidance products with the WAIP indicate almost all of the products are more accurate than WAIP over the South China Sea region. The statistical-dynamic consensus technique S5XX does have skill through 72 h for landfalling situations along the coasts of China and Southeast Asia. At 120 h, the WAIP has superior performance over the guidance products over most areas of the western North Pacific, but again the S5XX is more accurate than WAIP for landfalling tropical cyclones on the Philippine Islands, Southeast Asia, South China, and northeastern Japan. This information will be useful to the forecaster in deciding when and where (or how much) to rely on each guidance product in preparing the five-day intensity forecast once the official track forecast has been established.

Objective Verifications and False Alarm Analyses of Western North Pacific Tropical Cyclone Event Forecasts by the ECMWF 32-Day Ensemble

Hsiao-Chung Tsai,Russell L. Elsberry,Mary S. Jordan 한국기상학회 2013 Asia-Pacific Journal of Atmospheric Sciences Vol.49 No.4

An objective tropical cyclone (TC) track analog verification technique has been developed to select all ensemble storm tracks predicted by the ECMWF 32-day ensemble that match the overall Joint Typhoon Warning Center (JTWC) post-season best-tracks. Ensemble storms within specified time and space differences of each JTWC track are first extracted as potential analogs, and four metrics of shortest distance, average distance, distance at formation time, and distance at ending time are calculated. An objective quality measure that assesses the overall track similarity between the potential analogs and each JTWC track is calculated in terms of membership functions for the four track metrics. Weighting factors multiplying these membership functions are adjusted to match with the quality measures for the ECMWF ensemble storm forecasts in a previous subjective evaluation. Objective verifications for the 2009 and 2010seasons have been summarized in terms of Hits, Misses, False Alarms, and Correct Negatives that no TC would be present in the western North Pacific. The most important result is that the ECMWF ensemble was able to predict nearly all of the TCs in both seasons with only a small number of Misses that generally were short-lived tropical depressions. Good performance in terms of Correct Negatives was achieved during the 2010 season. False alarms are defined to be all ensemble storms that could not be matched any JTWC tracks within the specified thresholds. Evaluations of the characteristics of the false alarms indicate seasonal and geographic biases and that about 50% of the false alarm in the Week 1 forecasts originate from the initial the initial conditions in the model. A minimum of false alarms created in Week 2 forecasts is attributed to the decrease in horizontal resolution in the model that occurs at day 10. A steady and nearly uniform increase in false alarms in the Week 3 and Week 4forecasts may be attributed to net convective heating in response to persistent environmental forcing in the tropics.

Seven-Day Intensity and Intensity Spread Predictions for Western North Pacific Tropical Cyclones

Hsiao-Chung Tsai,Russell L. Elsberry 한국기상학회 2015 Asia-Pacific Journal of Atmospheric Sciences Vol.51 No.4

Our weighted-analog intensity (WANI) technique for predicting western North Pacific tropical cyclone intensity and with intensity spread guidance has been extended from five days to seven days. A perfect-prog approach that utilizes the Joint Typhoon Warning Center (JTWC) best-tracks is adopted and the 10 best historical track analogs are selected from the 1945-2009 JTWC besttrack file. A development sample from the 2000-2009 seasons is used to develop an intensity bias correction and an intensity spread calibration. Tests with an independent sample from the 2010-2014 seasons demonstrate that the intensity mean absolute errors and the correlation coefficients of the WANI forecast intensities with the verifying intensities essentially remain constant in the five-day to seven-day forecast interval. After calibration of the raw intensity spreads among the 10 historical analogs each 12 h, the uncertainty estimates about the WANI intensity forecasts also do not increase during the five-day to seven-day forecast intervals. The conclusion is that the seven-day WANI will provide intensity and intensity spread predictions of western North Pacific tropical cyclones with a similar performance as our five-day WANI technique. Examples of the performance for this seven-day WANI for westward-moving and northwestward-moving cyclones that make landfall, or for recurving storms that begin decay after rrecurvature over the ocean, demonstrate the value of constraining the intensities at the end of the WANI forecast. Less satisfactory WANI forecasts occur for rapid intensification, rapid decay, and for cyclones with extended periods of non-intensification.

Applications of Situation-Dependent Intensity and Intensity Spread Predictions Based on a Weighted Analog Technique

Hsiao-Chung Tsai,Russell L. Elsberry 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.4

A version of our situation-dependent intensity prediction (SDIP) is proposed for operational application after three modifications: (i) Ten historical track analogs are matched with Joint Typhoon Warning Center (JTWC) official track forecasts rather than besttracks; (ii) Giving two times as much weight to the 72 h - 120 h portion of the track as to the 0-72 h portion to give higher rankings for analog tracks with similar landfall or recurvature positions and timing; and (iii) Weighting both the intensity prediction technique and a new intensity spread guidance product according to new rankings of the track analogs rather than assuming all track analogs are equally likely. These special matchings and weightings of the track analogs in this weighted-analog intensity (WANI) add skill in the 72-120 h forecast intervals in regions where landfalls occur. Viability as an operational technique is demonstrated as the WANI has only 1 kt larger mean absolute errors than the JTWC intensity errors from 12 h through 72 h, and the WANI is 5 kt (20%) better at 120 h. The WANI rank-weighted intensity spreads each 12 h among the 10 best historical track analogs are processed to reduce any intensity bias and calibrated to reduce (increase) the over-determined (under-determined) intensity spreads at early (later) forecast intervals. Thus, the situation-dependent intensity spread guidance is generated that will include about 68% of the verifying intensities at all forecast intervals. Four examples of the WANI intensity predictions and intensity spread guidance are presented to illustrate how the forecaster might use this information in potential landfall and intensity bifurcation situations.

Improved Tropical Cyclone Intensity and Intensity Spread Prediction in Bifurcation Situations

Hsiao-Chung Tsai,Russell L. Elsberry 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.5

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.

Seven-Day Intensity and Intensity Spread Predictions in Bifurcation Situations with Guidance-On-Guidance for Western North Pacific Tropical Cyclones

Hsiao-Chung Tsai,Russell L. Elsberry 한국기상학회 2018 Asia-Pacific Journal of Atmospheric Sciences Vol.54 No.3

An objective technique to detect and predict intensity bifurcation situations in a five-day Weighted Analog Intensity forecast technique for the western North Pacific (WAIP) has been extended to seven days. A hierarchical cluster analysis is applied to the N analog intensities to separate them into two clusters, which are considered to represent a substantial intensity bifurcation if a threshold maximum velocity difference of 15 kt is satisfied. Two important modifications have been made to develop the bifurcation version for seven-day WAIP forecasts. First, the number of track analogs has been increased from 10 analogs to 16 analogs, which results in larger sample sizes and better performance. Second, separate intensity bias corrections are calculated for the two clusterWAIP forecasts rather than using the same 16-analog intensity bias correction. If an always perfect selection of the correct clusterWAIP forecast of each bifurcation situation is made, a substantial improvement in the intensity mean absolute errors is achieved relative to the originalWAIP forecasts based on all 16 of the best analogs. These perfect-cluster selectionWAIP forecasts have smaller bias errors and are more highly correlated with the verifying intensities at all forecast intervals through 168 h. Furthermore, the Probability of Detection is improved for the perfect-cluster selection and more realistic intensity spreads are specified. A simple guidance-on-guidance technique is demonstrated to assist the forecasters in selecting the correct WAIP cluster forecast in bifurcation situations.

RAPID, SPECIFIC, AND SENSITIVE ON-SITE DIAGNOSIS OF MICROSPORIDIAN Enterocytozoon hepatopenaei ON POCKIT<SUB>TM</SUB> SYSTEM, A FIELD-DEPLOYABLE TOOL

Simon Chung,Chen Su,Pin-Hsing Chou,Yun-Long Tsai,Pei-Yu Alison Lee,Hsiao-Fen Grace Chang 한국수산과학회 양식분과 2015 한국수산과학회 양식분과 학술대회 Vol.2015 No.5

Situation-Dependent Intensity Skill Metric and Intensity Spread Guidance for Western North Pacific Tropical Cyclones

Russell L. Elsberry,Hsiao-Chung Tsai 한국기상학회 2014 Asia-Pacific Journal of Atmospheric Sciences Vol.50 No.3

A situation-dependent intensity prediction (SDIP) technique is developed for western North Pacific tropical cyclones that is based on the average of the intensity changes from the 10 best historical track analogs to the Joint Typhoon Warning Center best-tracks. The selection of the 10 best track analogs is also conditioned on the current intensity, and it is demonstrated that for a subsample of current intensities less than or equal to 35 kt the intensity mean absolute errors (MAEs) and biases are smaller than for the greater than 35 kt intensity subsample. The SDIP is demonstrated to have advantages as an intensity skill measure at forecast intervals beyond 36 h compared to the current climatology and persistence technique that uses only variables available at the initial time. The SDIP has significantly smaller intensity MAEs beyond 36 h with an almost 20% reduction at 120 h, has significantly smaller intensity biases than the present skill metric beyond 12 h, and explains 36% of the intensity variability at 120 h compared to 20% explained variance for the current technique. The probability distributions of intensities at 72 h and 120 h predicted by the SDIP are also a better match of the distribution of the verifying observations. Intensity spread guidance each 12 h to 120 h is developed from the intensity spread among the 10 best historical track analogs. The intensity spread is calibrated to ensure that the SDIP forecasts will have a probability of detection (PoD) of at least 68.26%. While this calibrated intensity spread is specifically for the SDIP technique, it would provide a first-order spread guidance for the PoD for the official intensity forecast, which would be useful intensity uncertainty information for forecasters and decision-makers.