Forecasting of tropical cyclones ASANI(2022)and MOCHA(2023)over the Bay of Bengal-real time challenges to forecasters

This study examines the track and intensity forecasts of two typical Bay of Bengal tropical cyclones(TC)ASANI and MOCHA.The analysis of various Numerical Weather Prediction(NWP)model forecasts[ECMWF(European Centre for Medium range Weather Forecast),NCEP(National Centers for Environmental Prediction),NCUM(National Centre for Medium Range Weather Forecast-Unified Model),IMD(India Meteorological Department),HWRF(Hurricane Weather Research and Forecasting)],MME(Multi-model Ensemble),SCIP(Statistical Cyclone Intensity Prediction)model,and OFCL(Official)forecasts shows that intensity forecasts of ASANI and track forecasts of MOCHA were reasonably good,but there were large errors and wide variation in track forecasts of ASANI and in intensity forecasts of MOCHA.Among all model forecasts,the track forecast errors of IMD model and MME were least in general for ASANI and MOCHA respectively.Also,the landfall point forecast errors of IMD were least for ASANI,and the MME and OFCL forecast errors were least for MOCHA.No model is found to be consistently better for landfall time forecast for ASANI,and the errors of ECMWF,IMD and HWRF were least and of same order for MOCHA.The intensity forecast errors of OFCL and SCIP were least for ASANI,and the forecast errors of HWRF,IMD,NCEP,SCIP and OFCL were comparable and least for MOCHA up to 48 h forecast and HWRF errors were least thereafter in general.The ECMWF model forecast errors for intensity were found to be highest for both the TCs.The results also show that although there is significant improvement of track forecasts and limited or no improvement of intensity forecast in previous decades but challenges still persists in real time forecasting of both track and intensity due to wide variation and inconsistency of model forecasts for different TC cases.

An Evaluation of the Advanced Dvorak Technique (9.0) for the tropical cyclones over the North Indian Ocean

The Advanced Dvorak Technique(ADT)is used by tropical cyclone prediction centres around the world to accurately evaluate the intensity of tropical cyclones(TCs)from meteorological operational satellites.The algorithm development team has introduced new improvements to the objective ADT to further extend its capabilities and accuracy.A study has therefore undergone to evaluate the new edition of ADT(9.0)based on all the North Indian Ocean Tropical cyclones during 2018,2019 and 2020(Total 15 No.).It is found that ADT(9.0)performed well with the conformity of IMD’s best track T.No estimates.ADT is reasonably good in estimating the intensity for T≥4.0(VSCS to SuCS)and overestimate the intensity for T≤3.5(CS/SCS).

Characteristic features of Super Cyclone ‘AMPHAN’-observed through satellite images

Characteristic features of Super Cyclonic Storm(Su CS),AMPHAN which crossed West Bengal-Bangladesh Coast on May 20,2020 have been analyzed based on INSAT-3 D&passive microwave(PMW)images with special emphasis on eye characteristics and its relationship with intensity.These satellite images/products are analyzed to determine the centre of the cyclone,its intensity and the characteristics of the eye of the cyclone.It shows the characteristic variation of intensity of Su CS with geometric and thermal characteristics of the‘eye’.Precise changes in the eye features of the cyclone can be used for very short-range forecasting of the intensity of the cyclone.

Characteristics of fog in relation to tropical cyclone intensity: A case study for IGI airport New Delhi

Widespread catastrophic fog episodes in polluted northern India have been attributed to tropical cyclone activity in the Bay of Bengal&Arabian Sea;however,limited studies have been conducted on the effect of tropical cyclone intensity(’T’Numbers)on different fog characteristics in Indo Gangetic Basin,Northern India.In this study,different characteristics,including persistence,intensity,and areal extension,were analyzed at the Indira Gandhi International Airport,New Delhi during 1998-99,2013-14,and 2016-17.A high-intensity tropical cyclone(Severe to Very Severe Cyclonic Storm)has been found to significantly increase the persistence,intensity,and areal extension of fog by inducing strong subsidence over the IGI Airport/Indo-Gangetic Basin.This knowledge is vital for improving the short-term forecasting of fog in the IndoGangetic Basin of Northern India and will further support the Government agencies to take preventive safety measures and planning well in advance time.

Improvement of displacement error of rainfall and wind field forecast associated with landfalling tropical cyclone AMPHAN

Spatial distribution of rainfall and wind speed forecast errors associated with landfalling tropical cyclones(TC)occur significantly due to incorrect location forecast by numerical models.Two major areas of errors are:(i)over-estimation over the model forecast locations and(ii)underestimation over the observed locations of the TCs.A modification method is proposed for real-time improvement of rainfall and wind field forecasts and demonstrated for the typical TC AMPHAN over the Bay of Bengal in 2020.The proposed method to improve the model forecasts is a relocation method through shifting of model forecast locations of TC to the real-time official forecast locations of India Meteorological Department(IMD).The modification is applied to the forecasts obtained from the operational numerical model,the Global Forecast System(GFS)of IMD.Application of the proposed method shows considerable improvement of both the parameters over both the locations.The rainfall forecast errors due to displacement are found to have improved by 44.1%–69.8%and 72.1%–85.2%over the GFS forecast locations and over the observed locations respectively for the respective forecast lead times 48 h,72 h,and 96 h.Similarly,the wind speed forecasts have improved by 27.6%–56.0%and 63.7%–84.6%over the GFS forecast locations and over the observed locations respectively for the respective forecast lead times 60 h,72 h,and 84 h.The results show that the proposed technique has capacity to provide improved spatial distributions of rainfall and wind speed forecasts associated with landfalling TCs and useful guidance to operational forecasters.

A HWRF-POM-TC coupled model forecast performance over North Indian Ocean: VSCS TITLI & VSCS LUBAN

The HWRF-POM-TC coupled model is run operationally at India Meteorological Department(IMD).This study is first attempt to assess the IMD’s operational HWRF-POM-TC(Atmosphere-Ocean)coupled model forecast performance over North Indian Ocean(NIO).The two cyclonic storms one each in Arabian Sea and Bay of Bengal were examined.Among them,VSCS LUBAN formed over Arabian Sea(AS)and was followed by the formation of VSCS TITLI over Bay of Bengal(Bo B).It constituted a rare case whereby two VSCS have formed in the north Indian Ocean(NIO)simultaneously.The HWRF-POM-TC modeling system,which was developed at National Centers for Environmental Prediction(NCEP)based on Nonhydrostatic Mesoscale Model(NMM)dynamic core,was customized for NIO conditions.For the two storms,VSCS LUBAN&VSCS TITLI,28 and 15 consecutive 6-hourly HWRF model runs were performed.The HWRF-POM-TC coupled model showed great skill in forecasting of Track and Intensity for examined cyclones.The result shows that the model predicted the intensification and landfall of VSCS Luban&Titli in agreement with the best track data as made available by Cyclone Warning Division(CWD),India Meteorological Department which is also recognized as Regional Specialized Meteorological Center(RSMC)by WMO for NIO.

Forecasting tropical cyclone wind hazards and impacts:Summary from the Tenth International Workshop on Tropical Cyclones(IWTC-10)

In this paper,we summarizefindings from the Tenth International Workshop on Tropical Cyclones(IWTC-10)subgroup on forecasting wind hazards and impacts.We found that new approaches to TC wind hazard forecasts continue to be developed and are becoming an increasingly common product offered by operational centres.To add greater context to wind risk information for users,many operational and research centres are also working to develop impact-based forecasts that incorporate hazard,vulnerability,and exposure data.Efforts to develop tropical cyclone wind impact forecasts present resourcing challenges,and when compared to wind hazard forecasting,are generally still in their infancy.Overall,both operational and research centres are extending significant efforts to meet the strong public need for accurate predictions of TC wind hazards and impacts around the world.