scholarly journals A Tropical Cyclone Rapid Intensification Prediction Aid for the Joint Typhoon Warning Center’s Areas of Responsibility

2020 ◽  
Vol 35 (3) ◽  
pp. 1173-1185 ◽  
Author(s):  
John A. Knaff ◽  
Charles R. Sampson ◽  
Brian R. Strahl
Keyword(s):  
Tropical Cyclone ◽  
Real Time ◽  
North Pacific ◽  
Input Data ◽  
Western North Pacific ◽  
Rapid Intensification ◽  
Probabilistic Forecasts ◽  
Time Periods ◽  
Using Data ◽  
Joint Typhoon Warning Center

Abstract In late 2017, the Rapid Intensification Prediction Aid (RIPA) was transitioned to operations at the Joint Typhoon Warning Center (JTWC). RIPA probabilistically predicts seven rapid intensification (RI) thresholds over three separate time periods: 25-, 30-, 35-, and 40-kt (1 kt ≈ 0.51 m s−1) increases in 24 h (RI25, RI30, RI35, RI40); 45- and 55-kt increases in 36 h (RI45 and RI55); and 70-kt increases in 48 h (RI70). RIPA’s probabilistic forecasts are also used to produce deterministic forecasts when probabilities exceed 40%, and the latter are included as members of the operational intensity consensus forecast aid. RIPA, initially designed for the western North Pacific, performed remarkably well in all JTWC areas of responsibility (AOR) and is now incorporated into JTWC’s ever improving suite of intensity forecast guidance. Even so, making real-time operational RIPA forecasts exposed some methodological weaknesses such as overprediction of RI for weak/disorganized systems (i.e., systems with maximum winds less than 35 kt), prediction of RI during landfall, input data reliability, and statistical inconsistencies. Modifications to the deterministic forecasts that address these issues are presented, and newly derived and more statistically consistent models are developed using data from all of JTWC’s AORs. The updated RIPA is tested as it would be run in operations and verified using a 2-yr (2018–19) independent sample. The performance from this test indicates the new RIPA—when compared to its predecessor—has improved probabilistic verification statistics, and similar deterministic skill while using fewer predictors to make forecasts.

scholarly journals An Operational Rapid Intensification Prediction Aid for the Western North Pacific

2018 ◽  
Vol 33 (3) ◽  
pp. 799-811 ◽  
Author(s):  
John A. Knaff ◽  
Charles R. Sampson ◽  
Kate D. Musgrave
Keyword(s):  
Logistic Regression ◽  
Discriminant Analysis ◽  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Rapid Intensification ◽  
Linear Discriminant ◽  
Probabilistic Forecasts ◽  
Weighted Probability ◽  
Joint Typhoon Warning Center

Abstract This work describes tropical cyclone rapid intensification forecast aids designed for the western North Pacific tropical cyclone basin and for use at the Joint Typhoon Warning Center. Two statistical methods, linear discriminant analysis and logistic regression, are used to create probabilistic forecasts for seven intensification thresholds including 25-, 30-, 35-, and 40-kt changes in 24 h, 45- and 55-kt in 36 h, and 70-kt in 48 h (1 kt = 0.514 m s−1). These forecast probabilities are further used to create an equally weighted probability consensus that is then used to trigger deterministic forecasts equal to the intensification thresholds once the probability in the consensus reaches 40%. These deterministic forecasts are incorporated into an operational intensity consensus forecast as additional members, resulting in an improved intensity consensus for these important and difficult to predict cases. Development of these methods is based on the 2000–15 typhoon seasons, and independent performance is assessed using the 2016 and 2017 typhoon seasons. In many cases, the probabilities have skill relative to climatology and adding the rapid intensification deterministic aids to the operational intensity consensus significantly reduces the negative forecast biases.

scholarly journals Is the Number of Tropical Cyclone Rapid Intensification Events in the Western North Pacific Increasing?

SOLA ◽  
2020 ◽  
Vol 16 (0) ◽  
pp. 1-5 ◽  
Author(s):  
Udai Shimada ◽  
Munehiko Yamaguchi ◽  
Shuuji Nishimura
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Rapid Intensification

scholarly journals Multidecadal Variability of Tropical Cyclone Rapid Intensification in the Western North Pacific

2015 ◽  
Vol 28 (9) ◽  
pp. 3806-3820 ◽  
Author(s):  
Xidong Wang ◽  
Chunzai Wang ◽  
Liping Zhang ◽  
Xin Wang
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Trade Wind ◽  
Rapid Intensification ◽  
Multidecadal Variability ◽  
Heat Potential

Abstract This study investigates the variation of tropical cyclone (TC) rapid intensification (RI) in the western North Pacific (WNP) and its relationship with large-scale climate variability. RI events have exhibited strikingly multidecadal variability. During the warm (cold) phase of the Pacific decadal oscillation (PDO), the annual RI number is generally lower (higher) and the average location of RI occurrence tends to shift southeastward (northwestward). The multidecadal variations of RI are associated with the variations of large-scale ocean and atmosphere variables such as sea surface temperature (SST), tropical cyclone heat potential (TCHP), relative humidity (RHUM), and vertical wind shear (VWS). It is shown that their variations on multidecadal time scales depend on the evolution of the PDO phase. The easterly trade wind is strengthened during the cold PDO phase at low levels, which tends to make equatorial warm water spread northward into the main RI region rsulting from meridional ocean advection associated with Ekman transport. Simultaneously, an anticyclonic wind anomaly is formed in the subtropical gyre of the WNP. This therefore may deepen the depth of the 26°C isotherm and directly increase TCHP over the main RI region. These thermodynamic effects associated with the cold PDO phase greatly support RI occurrence. The reverse is true during the warm PDO phase. The results also indicate that the VWS variability in the low wind shear zone along the monsoon trough may not be critical for the multidecadal modulation of RI events.

Wind Structure Discrepancies between Two Best Track Datasets for Western North Pacific Tropical Cyclones

2016 ◽  
Vol 144 (12) ◽  
pp. 4533-4551 ◽  
Author(s):  
Jinjie Song ◽  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Shape Parameter ◽  
Surface Wind ◽  
Japan Meteorological Agency ◽  
Wind Structure ◽  
Linear Relationships ◽  
Wind Analysis ◽  
Joint Typhoon Warning Center

Abstract Symmetric and wavenumber-1 asymmetric characteristics of western North Pacific tropical cyclone (TC) outer wind structures are compared between best tracks from the Joint Typhoon Warning Center (JTWC) and the Japan Meteorological Agency (JMA) from 2004 to 2014 as well as the Multiplatform Tropical Cyclone Surface Wind Analysis (MTCSWA) product from 2007 to 2014. Significant linear relationships of averaged wind radii are obtained among datasets, in which both gale-force and storm-force wind radii are generally estimated slightly smaller (much larger) by JTWC (JMA) than by MTCSWA. These correlations are strongly related to TC intensity relationships discussed in earlier work. Moreover, JTWC (JMA) on average represents a smaller (greater) derived shape parameter than MTCSWA does, implying that JTWC (JMA) typically assesses a more compact (less compact) storm than MTCSWA. For the wavenumber-1 asymmetry, large differences among datasets are found regardless of the magnitude or the direction of the longest radius. JTWC estimates more asymmetric storms than JMA, and it provides greater wavenumber-1 asymmetry magnitudes on average. Asymmetric storms are most frequently oriented toward the east, northeast, and north in JTWC and MTCSWA, whereas they are most frequently oriented toward the southeast, east, and northeast in JMA. The direction of the longest gale-force (storm force) wind radius in JTWC is statistically rotated 18° (32°) clockwise to that in JMA. Although the wind radii in JTWC are of higher quality than those in JMA when using MTCSWA as a baseline, there remains a need to provide a consistent and reliable wind radii estimating process among operational centers.

scholarly journals Environmental Dynamical Control of Tropical Cyclone Intensity—An Observational Study

2007 ◽  
Vol 135 (1) ◽  
pp. 38-59 ◽  
Author(s):  
Zhihua Zeng ◽  
Yuqing Wang ◽  
Chun-Chieh Wu
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Maximum Intensity ◽  
Vertical Shear ◽  
Accurate Estimation ◽  
Rapid Intensification ◽  
Positive Contribution ◽  
Peak Intensity ◽  
Dynamical Control

Abstract The effects of two environmental dynamical factors, namely, the transitional speed and vertical wind shear, on tropical cyclone (TC) intensification, intensity, and lifetime peak intensity were analyzed based on observations in the western North Pacific during 1981–2003. In general, both the fast translation and strong vertical shear are negative to both TC intensification and the lifetime peak intensity. Both the very intense TCs and the TCs with rapid intensification rate are found only to occur in a narrow range of translational speeds between 3 and 8 m s−1, and in relatively weak vertical shear. The overwhelming majority of western North Pacific TCs reach their lifetime peak intensity just prior to recurvature where their environmental steering flow and vertical shear are both weak. The results show that few TCs intensified when they moved faster than 15 m s−1, or when their large-scale environmental vertical shear is larger than 20 m s−1. The intensification rate of TCs is found to increase with decreasing vertical shear while the majority of the weakening storms experience relatively strong vertical shear. Overall, strong vertical shear prohibits rapid intensification and most likely results in the weakening of TCs, similar to the fast storm translation. Based on the statistical analysis, a new empirical maximum potential intensity (MPI) has been developed, which includes the combined negative effect of translational speed and vertical shear as the environmental dynamical control in addition to the positive contribution of SST and the outflow temperature as the thermodynamic control. The new empirical MPI can not only provide more accurate estimation of TC maximum intensity but also better explain the observed behavior of the TC maximum intensity and help explain the thermodynamic and environmental dynamical controls of TC intensity. Implications of the new empirical MPI are discussed.

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