A Statistical Intra-Seasonal Prediction Model of Extended Boreal Summer Western North Pacific Tropical Cyclone Genesis

2022 ◽  
pp. 1-59
Author(s):  
Ying Lu ◽  
Xianan Jiang ◽  
Philip J. Klotzbach ◽  
Liguang Wu ◽  
Jian Cao
Keyword(s):  
Logistic Regression ◽  
Tropical Cyclone ◽  
Regression Model ◽  
North Pacific ◽  
Western North Pacific ◽  
Logistic Regression Model ◽  
Boreal Summer ◽  
Time Varying ◽  
Model Skill ◽  
Skill Scores

Abstract A L2 regularized logistic regression model is developed in this study to predict weekly tropical cyclone (TC) genesis over the western North Pacific (WNP) and sub-regions of the WNP including the South China Sea (SCS), the western WNP (WWNP), and the eastern WNP (EWNP). The potential predictors for the TC genesis model include a time-varying TC genesis climatology, the Madden-Julian oscillation (MJO), the quasi-biweekly oscillation (QBWO), and ENSO. The relative importance of the predictors in a constructed L2 regression model is justified by a forward stepwise selection procedure for each region from a 0-week to a 7-week lead. Cross-validated hindcasts are then generated for the corresponding prediction schemes out to a 7-week lead. The TC genesis climatology generally improves the regional model skill, while the importance of intra-seasonal oscillations and ENSO are regionally dependent. Over the WNP, there is increased model skill over the time-varying climatology in predicting weekly TC genesis out to a 4-week lead by including the MJO and QBWO, while ENSO has a limited impact. On a regional scale, ENSO and then the MJO and QBWO respectively, are the two most important predictors over the EWNP and WWNP after the TC genesis climatology. The MJO is found to be the most important predictor over the SCS. The logistic regression model is shown to have comparable reliability and forecast skill scores to the ECMWF dynamical model on intra-seasonal time scales.

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 Characterizing the highest tropical cyclone frequency in the Western North Pacific since 1984

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Joseph Basconcillo ◽  
Eun-Jeong Cha ◽  
Il-Ju Moon
Keyword(s):  
Tropical Cyclone ◽  
Summer Monsoon ◽  
North Pacific ◽  
Western North Pacific ◽  
Tropical Indian Ocean ◽  
Boreal Summer ◽  
Central Pacific ◽  
Impact Reduction ◽  
Cyclone Frequency ◽  
Sst Anomalies

AbstractThe 2018 boreal summer in the Western North Pacific (WNP) is highlighted by 17 tropical cyclones (TC)—the highest record during the reported reliable years of TC observations. We contribute to the existing knowledge pool on this extreme TC frequency record by showing that the simultaneous highest recorded intensity of the WNP summer monsoon prompted the eastward extension of the monsoon trough and enhancement of tropical convective activities, which are both favorable for TC development. Such changes in the WNP summer monsoon environment led to the extreme TC frequency record during the 2018 boreal summer. Meanwhile, the highest record in TC frequency and the intensity of the WNP summer monsoon are both attributed with the combined increase in the anomalous westerlies originating from the cold tropical Indian Ocean sea surface temperature (SST) anomalies drawn towards the convective heat source that is associated with the warm central Pacific SST anomalies. Our results provide additional insights in characterizing above normal tropical cyclone and summer monsoon activities in the WNP in understanding seasonal predictable horizons in the WNP, and in support of disaster risk and impact reduction.

scholarly journals Subseasonal Tropical Cyclone Genesis Prediction and MJO in the S2S Dataset

2018 ◽  
Vol 33 (4) ◽  
pp. 967-988 ◽  
Author(s):  
Chia-Ying Lee ◽  
Suzana J. Camargo ◽  
Fréderic Vitart ◽  
Adam H. Sobel ◽  
Michael K. Tippett
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
South Pacific ◽  
Seasonal Prediction ◽  
Skill Score ◽  
Ensemble Prediction ◽  
Tropical Cyclone Genesis ◽  
Probabilistic Prediction ◽  
Skill Scores

Abstract Subseasonal probabilistic prediction of tropical cyclone (TC) genesis is investigated here using models from the Seasonal to Subseasonal (S2S) Prediction dataset. Forecasts are produced for basin-wide TC occurrence at weekly temporal resolution. Forecast skill is measured using the Brier skill score relative to a seasonal climatology that varies monthly through the TC season. Skill depends on models’ characteristics, lead time, and ensemble prediction design. Most models show skill for week 1 (days 1–7), the period when initialization is important. Among the six S2S models examined here, the European Centre for Medium-Range Weather Forecasts (ECMWF) model has the best performance, with skill in the Atlantic, western North Pacific, eastern North Pacific, and South Pacific at week 2. Similarly, the Australian Bureau of Meteorology (BoM) model is skillful in the western North Pacific, South Pacific, and across northern Australia at week 2. The Madden–Julian oscillation (MJO) modulates observed TC genesis, and there is a relationship, across models and lead times, between models’ skill scores and their ability to accurately represent the MJO and the MJO–TC relation. Additionally, a model’s TC climatology also influences its performance in subseasonal prediction. The dependence of the skill score on the simulated climatology, MJO, and MJO–TC relationship, however, varies from one basin to another. Skill scores increase with the ensemble size, as found in previous weather and seasonal prediction studies.

scholarly journals Recent Strengthening of the Relationship between the Western North Pacific Monsoon and Western North Pacific Tropical Cyclone Activity during the Boreal Summer

2019 ◽  
Vol 32 (23) ◽  
pp. 8283-8299 ◽  
Author(s):  
Haikun Zhao ◽  
Shaohua Chen ◽  
Philip J. Klotzbach
Keyword(s):  
Tropical Cyclone ◽  
North Pacific ◽  
Western North Pacific ◽  
Southern Oscillation ◽  
Phase Relationship ◽  
Boreal Summer ◽  
Central Pacific ◽  
Enso Events ◽  
The Pacific ◽  
Phase Out

Abstract This study examines the association between the western North Pacific (WNP) summer monsoon (WNPSM) and WNP tropical cyclone (TC) frequency during June–August from 1979 to 2016. The interannual relationship between the WNPSM and the total number of WNP TCs has strengthened since 1998. There has also been a significant reduction in the number of TCs forming within the WNP monsoon trough (WNPMT)—hereafter called ITCs, for internal or inside TCs—since 1998. These two important features are found to be closely associated with the climate regime shift that occurred around 1998. During 1998–2016, the Pacific decadal oscillation (PDO) tended to be in a cold phase, with an increasing occurrence of central Pacific–type El Niño–Southern Oscillation (ENSO) events, whereas the 1979–97 period tended to be characterized by a warm phase of the PDO and east Pacific–type ENSO events. During 1998–2016, the tropical Pacific was characterized by enhanced easterlies, which led to a westward-retreated WNPMT that caused a significant decrease in ITCs over the WNP basin. However, there was little change in TCs outside of the WNPMT region (hereafter called OTCs) compared to that before 1998. A significant in-phase (out-of-phase) relationship between the WNPSM and the number of ITCs (OTCs) is observed before 1998, thus greatly weakening the WNPSM–TC relationship. The recent enhanced relationship between the WNPSM and TCs is mainly due to a strong in-phase relationship between the WNPSM and ITCs. The interannual change in ITCs is mainly controlled by WNPSM changes since 1998, while OTC changes are mainly modulated by changes in the tropical upper-tropospheric trough.

scholarly journals How Significant are Low-Level Flow Patterns in Tropical Cyclone Genesis over the Western North Pacific?

2020 ◽  
Vol 148 (2) ◽  
pp. 559-576 ◽  
Author(s):  
Ryuji Yoshida ◽  
Hironori Fudeyasu
Keyword(s):  
Tropical Cyclone ◽  
Flow Pattern ◽  
North Pacific ◽  
Western North Pacific ◽  
Flow Patterns ◽  
Lower Latitude ◽  
Boreal Summer ◽  
Tropical Cyclone Genesis ◽  
Low Level ◽  
Cyclone Genesis

Abstract The low-level flow pattern characteristics of the tropical cyclone genesis (TCG) environment over the western North Pacific (WNP) were investigated not only for the periods during which TCG occurred, but also for the periods during which no TCG occurred. The flow patterns investigated were the shear line (SL), confluence region (CR), and easterly wave (EW) patterns. Although these flow patterns are recognized as favorable environmental conditions for TCG, their general characteristics, such as the climatological horizontal distribution, have not been previously investigated and there has been no comparison of the significance of the TCG cases to the climatological mean. We examined flow patterns using flow pattern indices defined by the modified semiobjective analysis method. SL and CR were broadly distributed over the WNP east of the Philippines during the boreal summer season. There was a peak in the EW from summer to autumn and it was distributed in a band running in an east–west direction at a lower latitude. Flow pattern indices of all three flow patterns gradually intensified until the TCG date was reached. The SL and EW indices became more intense compared to the climatological mean one day before the TCG, while that of the CR did not exceed the climatological mean. TCG occurred at the eastern edge of the area with a high genesis potential index and relative humidity and a weak vertical shear over flow patterns. This determination of the general characteristics of favorable flow pattern conditions improves our understanding of the TCG process.

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