Editor’s note: For easy download the posted pdf of the State of the Climate for 2019 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

The impact of strong La Niña events on January–February North Atlantic mean sea level pressure is unknown, as these events have never been observed. Using large ensembles from the Met Office decadal prediction system, examples of strong La Niña events are simulated and the Atlantic response to these is found to be a positive North Atlantic Oscillation. This is very different to the wavelike response observed and simulated for strong El Niño events. The reason for this difference is traced to the fact that the December‐January‐February mean tropospheric teleconnection of El Niño–Southern Oscillation to the North Atlantic dominates for strong El Niño events, while the stratospheric teleconnection dominates for strong La Niña events. The strength of the tropospheric pathway grows linearly and symmetrically with El Niño–Southern Oscillation. The stratospheric pathway is the source of the asymmetry between January and February surface responses to strong El Niño and strong La Niña events.

Korean winter temperature exhibits significant year-to-year variability, an extreme example of which was the severe cold winter of 2012/2013. Such events can have significant societal and financial impacts. We investigate the seasonal forecast skill for Korean winter temperature using Met Office initialised climate prediction systems. We find significant skill using two independent hindcasts covering the last decades. Observed Korean winter temperature variability appears to be driven by large-scale dynamical circulation anomalies with centers over the northwest Pacific High (PH) and the Siberian High (SH). While the model has a good simulation of these observed teleconnections, we find that skilfully predicted PH variability dominates the model skill. This is due to the relatively strong PH teleconnection to highly predictable tropical Pacific and Indian Ocean variability. Whereas, observed SH variability is currently much less predictable in seasonal forecast systems. Furthermore, we find that the modelled SH exhibits lower predictability than the observed SH, suggesting a model "signal-to-noise" problem over extratropical East Asia which is similar to that reported over northern Europe. We explore one possible pathway, the representation of stratosphere-troposphere coupling, by examining the model simulation of stratospheric sudden warming (SSWs) events. While the SSW frequency and the spatial pattern of surface circulation response appears well simulated, the amplitude of the model response over SH appears anomalously weak. Nevertheless, we conclude that current seasonal forecasts of Korean winter temperature are skilful and have the potential to provide useful climate services.

Purpose -In operational tropical cyclone (TC) forecasting practice, there are usually many TC track guidances available from various official sources. When they do not converge, the guidances need to be ensembled by systematic approaches to formulate the best possible track as an official local TC track forecasting. Design/methodology/approach -The main approach of the research is focused on finding an atmospheric environment favourable for TC survival (genesis) with the help of commonly accepted knowledge in atmospheric physics that reveals mechanism driving evolution and change of synoptic patterns in the atmosphere, using routinely available observational data, i.e. identification of TCF/TCR areas. The techniques developed are then applied to ensemble the TC track guidances available operationally to formulate an official TC track forecasting. Findings -The results show that TC movement is very dependent on the atmospheric environment surrounding a TC. Whether the environment is favourable (TCF) or resistant (TCR) to survival of a TC system is a vital factor to determine where the TC moving. A systematic approach to the identification of the TCR/TCF areas is a key technique to ensemble available TC track guidances to formulate an official TC track forecasting. Originality/value -In operational TC forecasting, TC track forecasting is the most important and difficult issue. The results indicate that the systematic approach to TC track forecasting has philosophical justification, solid scientific ground, sound logic and practical viability, and thus, make TC track forecasting easy and effective.