This review summarizes the rapporteur report on advances in monitoring and forecasting of rainfall associated with tropical cyclones (TCs) and its impact during 2014-18, as presented to the 10th International Workshop on TCs (IWTC-10) held in Bali, Indonesia during 5th - 9th December 2022. Major physical processes that can modulate TC rainfall distribution, including topography, storm motion, vertical wind shear, and intensity, along with the fundamental physics of rain bands and clouds as simulated by numerical models, diurnal variation of rainfall, and various synoptic and mesoscale features controlling the rainfall distribution are briefly discussed. Improvements to the dynamic core and physical processes in global models are providing useable forecasts nearly up to 7 days. This report also summarizes, some tools that have been developed to predict TC rainfall. Lately there is a tendency for operational forecasting centers to utilize multi-model ensemble systems for rainfall forecasting that demonstrate superior performance than individual models, ensemble members, or even single model ensembles. Major impacts include pluvial and fluvial floods, and landslides. The techniques developed by various forecasting centers to assist in predicting and communicating the impacts associated with these events are also presented in this report. & COPY; 2023 The Shanghai Typhoon Institute of China Meteorological Administration. Publishing services by Elsevier B.V. on behalf of KeAi Communication Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The prolonged positive phase of the Arctic Oscillation (AO) and associated quasi-stationary equivalent barotropic Euro-Atlantic blocking high (EABH) and the Siberian high (SH) existed during January 2020. The presence of the persistent quasi-stationary barotropic high resulted in higher (lower) than normal surface temperatures in most parts of northern (southern) Eurasia. The large-scale analysis suggests the detouring of the mid-latitudinal westerlies from EABH and the formation of the west–east trough from East Atlantic to Northwest Pacific across North Africa, the Middle East, North India and China. The convergence of the moisture and positive convection anomalies along the region of the trough is perceived from the analysis. In the backdrop of this large-scale circulation anomalies, higher than normal precipitation was received in most of the central and north Indian regions with thunderstorms/hailstorm events. The variations in the AO index (AOI) and EABH were found to be in concurrence with the precipitation anomalies over the Indian region. The detailed analysis of a selected thunderstorm/hailstorm case suggests that the lowering of the 0 °C isotherm due to the intrusion of mid-latitudinal westerlies and the development of atmospheric instability with moisture supply from the adjacent seas facilitated the occurrence of the thunderstorms/Hailstorm events during January 2020.

This study examines the interannual variability of South Asian summer monsoon rainfall (SAMR) using a linear trend analysis for the recent 17-year period from 2000 to 2016. The trends in SAMR analyzed from multiple rainfall datasets show a unique crisscross like pattern over South Asia and its surrounding oceans. Significant positive trends in SAMR occur over the middle and south Bay of Bengal (BOB) and North-West India (NWI) aligned in SE-NW direction. Similarly, significant negative trends are observed over North-East India and head Bay of Bengal (NEI) as well as over the middle and south Arabian Sea (AS) oriented in SW-NE direction. Western Ghats make an exception to this pattern, where significant positive trends have been observed. Interestingly, the trends in aerosol optical depth (AOD) for the same period closely follow the trends in SAMR. The relationship of AOD averaged over each of the significant aerosol trend regions with the SAMR suggest aerosol induced suppression in moisture transport from a region covering Southern Arabian Sea and Bay of Bengal played a dominant role over the negative trend regions. However, the decreased aerosols over the Northwest India due to significant positive trends in rainfall reduced dust transport from the Arabian Peninsula towards eastern parts of South Asia resulting in an increase in anthropogenic aerosols from local sources. This caused significant drying over the NEI and AS regions through aerosol indirect effects. Further, Aerosol direct radiative effects due to natural and anthropogenic sources inferred from the climate forcing estimates confirmed their role in positive trends and the indirect effects inferred from satellite cloud products depicted a strong association with negative trends, thus maintaining the observed crisscross pattern.

The chapter discusses the patterns of weather and climate in the Arctic region. The chapter starts with a brief introduction to the Arctic and the geography. Section 2.3 has many subsections, wherein the synoptic conditions causing different weather over the region and the pattern of variability (monthly and seasonal) of the state parameters along with precipitation are discussed. Also, the climatic pattern (for longer time duration) of these parameters is also analysed and discussed using NCEP/NCAR reanalysis dataset. The following Section 2.3.7 discusses the recent observations and trends obtained from the data collected by the Indian researchers during various Arctic expeditions, and the subsection 2.3.8 deals with the effect of Arctic weather and climate on the Northern Hemispheric weather and climate patterns. The impact of climate change is taking a toll on the fragile Arctic ecosystem, and it is being discussed in the subsection 2.3.9. Finally, a summary on the Indian Arctic Programme conducted by the National Centre for Polar and Oceanic Research (NCPOR) is given.

While destruction associated with floods during the monsoon season and cyclones receives wide attention, the extreme weather in the form of hail, lightning and high winds have also caused widespread devastation over India on a small spatial scale in recent years, especially during the period of March to June. India Meteorological Department (IMD) organized a special forecast improvement campaign during the period March to June of 2017–2019 when the weather forecasts at all offices of IMD were targeted towards an accurate forecast of the extreme form of thunderstorms and their associated impact in short range to nowcasting timescale and their dissemination. The purpose of this study is to quantify the improvement in operational thunderstorm forecast accuracy, in short range (24 h Severe Weather Guidance at subdivisional level) and nowcast scale (nowcasts for individual stations valid for 3 h and issued every three hours) during March to June of 2017 to 2019 and compare the same with the accuracy of previous years. As a result of these efforts, there has been a significant jump in forecast accuracy in the 24-h thunderstorm forecast as well as 3-h nowcast guidance for thunderstorms across the country. Probability of Detection (POD) scores for India as a whole for the 24-h thunderstorm forecast has doubled, while the false alarms (FAR) have remained at the same level as before the start of the forecast campaign. The results indicate that since a thunderstorm is a disastrous weather event, the forecasters generally tend towards spatial over-forecasting. However, this is not uniform across the months. There is systematic lower accuracy in the season transition months of March (winter to summer) and June (dry summer to wet summer). While POD decreases in both March and June, FAR decrease throughout the season. The significant evolution of atmospheric parameters (moisture in particular) as the season changes, favours the maturation of thunderstorms to cumulonimbus stage as the season progresses, and the problem of over forecasting in March becomes a problem of under forecasting of thunderstorms in June. Another reason for false alarms is the unconscious linkage of the thunderstorm with the pattern of rainfall occurrence. However, since all rain-giving clouds over India do not necessarily mature to the cumulonimbus stage, and vice versa, the two are not always related. This is particularly true for the more arid regions of the country, especially in March, where false alarms are higher. The poor density of reporting observatories compared to the mesoscale nature of the events may also increase false alarms, especially over the small maritime islands and the arid regions of the mainland. The accuracy of the All India 3 hourly station level nowcast also improved systematically since 2017. Despite these constraints, the improvements at all scales were possible due to (a) augmentation of observation network by the rapid expansion of Doppler radars network throughout the Indian mainland as well as the installation of a ground-based lightning detection network, (b) numerical modeling products introduced in 2019 to provide short-range forecasts for all aspects of convection; both of which are incorporated into the forecast framework through Standard Operating Procedures (SOP) to standardize the forecast procedure throughout the Indian region. A more objective forecast strategy, using data generated from a denser network of DWRs and crowdsourcing methods as well as more accurate mesoscale models will go a long way to further improve the thunderstorm forecasts.

India Meteorological Department (IMD) categorises the tropical cyclones (TCs) as cyclonic storm (CS), severe cyclonic storm (SCS), very severe cyclonic storm (VSCS), extremely severe cyclonic storm (ESCS) and super cyclonic storm (SuCS). The long term climatology of TCs in these categories and the trends in frequency and intensity of TCs in these categories developing over the NIO and crossing different coastal regions are limited. Hence a study has been undertaken to analyse the characteristics of genesis and intensification of CDs in the above categories developing over the NIO and crossing different coastal regions based on the data of satellite era (1965-2020). The most intense TCs (ESCS & above) cross the coast maximum over Odisha (ODS) followed by Andhra Pradesh (AP)/Myanmar (MMR) & Bangladesh (BDS) and low intensity TCs (CS/SCS) cross maximum over BDS followed by AP, ODS & Tamilnadu (TN) and medium intensity TCs (VSCS) cross maximum over TN/AP/BDS followed by ODS/West Bengal (WB)/MMR during a year as a whole. While maximum CS/SCS cross BDS, maximum VSCS cross BDS/MMR and maximum ESCS cross MMR coast during pre-monsoon season. While maximum CS/SCS/VSCS cross AP coast, maximum ESCS cross ODS coast during post monsoon season. Over the AS, the landfall frequency of VSCS is maximum over Arabia - Africa (AA) coast followed by Saurashtra and Kutch coast. The coastal vulnerability due to ESCS continues over the Bay of Bengal (BoB) region, as there is no significant trend in the frequency of genesis of ESCS and above intensity storms, though there is decreasing trend in the genesis frequency of D/DD, CS, SCS, VSCS over the BoB. It has increased over the AA coast due to increasing trend in frequency of genesis of VSCS and above intensity storms over Arabian Sea.

Indian summer monsoon of 2015 was deficient with prominence of short-lived (long-lived) active (break) spells. The real-time extended range forecasts disseminated by Indian Institute of Tropical Meteorology using an indigenous ensemble prediction system (EPS) based on National Center for Environmental Predictions’s climate forecast system could broadly predict these intraseasonal fluctuations at shorter time leads (i.e. up to 10 days), but failed to predict at longer leads (15–20 days). Considering the multi-scale nature of Indian Summer Monsoon system, this particular study aims to examine the inability of the EPS in predicting the active/break episodes at longer leads from the perspective of non-linear scale interaction between the synoptic, intraseasonal and seasonal scale. It is found that the 2015 monsoon season was dominated by synoptic scale disturbances that can hinder the prediction on extended range. Further, the interaction between synoptic scale disturbances and low frequency mode was prominent during the season, which might have contributed to the reduced prediction skill at longer leads.

Among the extreme weather events hailstorm in recent past caused significant crop damage across the country. In 2014 and 2015 unseasonal rains and hailstorms during March and April damaged rabi crops as well as horticultural crops extensively in many parts of the country. In this paper, a detailed analysis of occurrence of hailstorm in four homogenous regions of India during past 35 years from 1981 to 2015 has been made, to find out the climatological and favourable synoptic aspects associated with hailstorms so that timely issuing of warning and Agromet Advisories could minimize the crop damage/loss. Maximum hailstorms were observed to have occurred in Maharashtra (31 years) during the period of study with highest occurrence of 11 days during 24 February to 14 March, 2014. Also Maharashtra is more prone to hailstorms than other States in the country with maximum probability of occurrence (91-95%) while the probability of occurrence (6-10%) is least in Gujarat, Chhattisgarh, Tamil Nadu, Tripura, Meghalaya, Sikkim and Nagaland. The significant synoptic situations associated with occurrence of hailstorms are found to be the north-south line of wind discontinuity causing convective activity and systems in westerlies. The information generated in this study was found to be very useful in minimizing crop loss through operational agromet services launched by the India Meteorological Department/Ministry of Earth Sciences in collaboration with the Agromet Field Units (AMFUs) located at State Agricultural Universities and institutes of ICAR and IITs under the project Gramin Krishi Mausam Sewa (GKMS).

During 2016, in all 10 intense low pressure systems formed over the Indian Seas. These include; one Very Severe Cyclonic Storm (VSCS) ‘VARDAH’, 3 Cyclonic Storms (ROANU, KYANT and NADA), 2 Deep Depressions and 4 Depressions. Out of these 10 systems, seven systems formed over the Bay of Bengal, two over the Arabian Sea and one over Land. One Cyclonic Storm over the Bay of Bengal formed in Pre monsoon season. Monsoon Season witnessed two Deep depressions over the Bay of Bengal and two Depressions, one over the Arabian Sea and one over land. Post-monsoon season was cyclogenically active with successive formations of Cyclonic Storms (KYANT and NADA) and VSCS ‘VARDAH’ over the Bay of Bengal.

Unprecedented, widespread, and devastating hailstorms occurred during February and March 2014 over north peninsular India (study area). A diagnostic study has been carried out to understand the causes for the same. Over the study area the atmosphere was convectively unstable due to the incursion of warm and moist air from Bay of Bengal and Arabian Sea which was overlaid by cold and dry midlatitude westerlies caused due to the unusual upper oceanic heat content of the Pacific Ocean. At the surface and lower levels, anticyclonic flow over the central India produced easterly winds and cyclonic circulation over Arabian Sea at 850 hPa level produced westerly winds over the peninsular India. Meeting of these winds caused convergence of moist air in the lower levels. The troughs in the upper level westerlies provided the divergence in the upper levels. As a consequence of this convergence/divergence structure, synoptic‐scale slow rising motion occurred over the study region. This released the convective instability to cause deep and wide convection with cloud bases at ~1500 m above mean sea level and tops well above the freezing level. Release of latent heat of deposition of water vapor provided extra buoyancy and produced strong updrafts causing explosive growth of the clouds reaching to very high levels and formation of large hails in the clouds. This atmospheric setup was a result of combined effect of planetary and synoptic forcings which persisted for ~3 weeks.

Post monsoon season 2019 was cyclogenetically an active season in the Arabian Sea which witnessed the formation of 5 intense low-pressure systems of the total 6 in the North Indian Ocean (NIO) comprising of the Bay of Bengal and the Arabian Sea.The 5 systems formed in the Arabian Sea, included two Deep Depressions, one Cyclonic Storm, one Extremely Severe Cyclonic Storm and one Super Cyclonic storm.The year as a whole also witnessed development of more intense cyclones over the Arabian Sea corresponding with strongly positive Indian Ocean Dipole.However, the cyclone activity over the Bay of Bengal during 2019 had been slightly subdued, as only 3 cyclones formed against the normal of 4 per year.In a first since 1965, two cyclones occurred, simultaneously in the Arabian Sea, with the formation of Cyclone 'MAHA' (30 th October -7 th November), even as Super Cyclonic Storm 'Kyarr' (24 th October -2 nd November) prevailed over the region.Likewise, Extremely Severe Cyclonic Storm 'MAHA' co-existed with Very Severe Cyclonic Storm (VSCS) 'BULBUL' over the Bay of Bengal during 5-7 November.Similarly, co-existence of Cyclonic Storm 'Pawan' over southwest Arabian Sea and a deep depression over southeast Arabian Sea in the first week of December, is the second such event after super cyclonic storm 'Kyarr' and extremely severe cyclonic storm 'MAHA'.Cyclone 'Kyarr' was the second super cyclone formed over the Arabian Sea after Cyclone 'Gonu' in 2007 during the period of 1965-2019.The super cyclonic storm 'Kyarr', Extremely Severe Cyclonic Storm 'MAHA' and the cyclonic storm 'Pawan' did not cause any major damage to any of the States of India.The VSCS 'Bulbul' which formed over the Bay of Bengal, crossed West Bengal coast close to Sunderban Forest.Even after landfall its intensity remained maintained for 4 more hours after crossing and subsequently it maintained the cyclonic storm intensity for subsequent 9 hours over the land owing to its proximity with Sea water resulting in widespread damage in the coastal districts of West Bengal and Odisha.Weather related disasters that occurred over the country during this season were due to heavy rainfall, lightning, cold wave, dense fog and low visibility.

This paper discusses the energetics aspects of two tropical cyclones formed over the north Indian Ocean during 2007, viz., the Super Cyclonic Storm (GONU) and the Very Severe Cyclonic Storm (SIDR). From the analysis of various energetics terms such as the Eddy Available Potential Energy (AE), Zonal Available Potential Energy (AZ), Zonal Kinetic Energy (KZ), Eddy Kinetic Energy (KE) and their generation and inter-conversions i.e., G(AE), G(AZ), C(AE, KE), C(AZ, KZ), C(KZ, KE) and C(AZ, AE) have been computed on day to day basis during the periods of their intensifications over the domain 5° N to 25° N, 55° E to 75° E in respect of ‘GONU’ and 5° N to 25° N, 77° E to 97° E for ‘SIDR’. Besides the above, the area averaged value of s (Sigma), the vertically averaged Moist Static Energy (MSE), has also been computed on each day. Day-to-day evolution of these parameters is mapped and described. Some of the distinguishing features in the energetic of these two intense vortices which formed in entirely different climatological settings have been brought out. It is noticed that in the case of ‘GONU’, though both barotropic and baroclinic energy conversions have taken place during the life cycle, the intensification phase is characterized by an enhancement in AE, KE and vertically integrated Moist Static Energy. Enhancement in AE can be attributed to the generation of AE, which may again be attributed to the asymmetric latent heat of condensation associated with the asymmetric rainfall in the cyclone field. Enhancement in KE may be attributed to the enhancement in both barotropic and baroclinic conversion into KE. Though most of these observations made for ‘GONU’ are found to be attributable to ‘SIDR’ as well, the intensification of ‘SIDR’ appears to have more similarity to that of a typical growing mid-latitude baroclinic wave. In this case, the enhancement in AE, could also be attributed to positive C(AZ,AE), which is mainly due to interaction with mid-latitude baroclinic westerly wave. The energetics analysis also indicates that GONU had helped in the enhancement of seasonal mean meridional circulation where as the SIDR had inhibited the enhancement of seasonal mean meridional circulation.