The cold surge or meridional surge (MS) is known to be one of the main features that contributes to extreme Malaysian rainfall events during the boreal winter or northeast monsoon. This study investigates other factors that contribute to the heavy rainfall, besides the cold surge, as well as their impacts on rainfall in the Malaysian region. Based on known methods, two additional types of surge are identified, namely the easterly surge (ES) and the mixed surge (MES), which is a mixture of both ES and MS. Daily average wind data from the European Centre for Medium‐Range Weather Forecasts Reanalysis ERA‐Interim for 37 seasons of the northeast monsoon (1979–1980 to 2016–2017, October–March) were used to identify the MSs, ESs and MESs. The impact of these surges on rainfall in the Malaysian region was investigated by using the rainfall data from the meteorological stations of the Malaysian Meteorological Department and the Tropical Rainfall Measuring Mission. The results showed that the MS plays an important role in modulating heavy rainfall in the early season over the east coast of Peninsular Malaysia. Meanwhile, the ES dominates the rainfall distribution over Sarawak in the late middle season. The rainfall modulated by the MES shows a higher intensity and concentrates over the southern part of the east coast of Peninsular Malaysia and Sabah. These findings provide a climatological view of the spatial and temporal distribution of heavy rainfall associated with different types of surge, which can be used as a forecasting tool for predicting surges and their impacts.

Borneo Squall Line (BSL) is a disaster risk associated with intense rain and wind gust that affect the activities and residence near the northern coast of Borneo. Using 3-hourly rainfall from Tropical Rainfall Measuring Mission (TRMM) 3B42V7 during southwest monsoon season (May–September) from 1998–2018, a total of 629 squall days were identified. Their monthly and annual average was 6 and 30 days, respectively, with July representing the month with the highest number of squall line days. BSL is frequently initiated during midnight/predawn and terminated in the morning. Composite analyses of BSL days using the daily winds from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim revealed that lower tropospheric wind convergence is a crucial controlling factor for BSL formation. The position of the monsoon trough closer to the equatorial South China Sea (SCS), and strong westerly and south-westerly winds played an important role in creating this wind convergence region. Analyses of tropical cyclone (TC) data from the Regional Specialized Meteorological Centre (RSMC), Tokyo showed that nearly 72% of BSL occurred with the presence of TC. Spectral analysis exhibited prominent frequencies mainly in the 3–4- and 6-year time scale, which likely reflected the influence of interannual modulation of El-Niño Southern Oscillation (ENSO). Correlation coefficient between squall days and Sea Surface Temperature (SST) anomalies indicated that BSL increased after La-Niña events. This study is expected to have implications for real-time squall line forecasting in Malaysia and contributes toward a better understanding of BSL.