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Marine heatwaves (MHWs) have been reported often throughout the world, producing severe effects on marine ecosystems. However, the spatial pattern and trend of MHWs in the Gulf of Thailand (GOT) is still unknown. Based on high-resolution daily satellite data over a 40-year period from 1982 to 2021, changes in annual mean SST and MHW occurrences across the GOT are explored here. The results demonstrate that during a warming hiatus (1998–2009), annual mean SST in the GOT encountered a dropping trend, followed by an increasing trend during a warming reacceleration period (2010–2021). Although a warming hiatus and a warming reacceleration occurred in the annual mean SST after 1998, regional averaged SSTs were still 0.18 °C–0.42 °C higher than that for 1982–1997. Statistical distributions reveal that there was a significant shift in both annual mean SSTs and annual extreme hot SSTs. These changes have the potential to increase the frequency of MHWs. Further analysis reveals that MHW frequency has increased at a rate of 1.11 events per decade from 1982 to 2021, which is 2.5 times the global mean rate. For the period 2010–2021, the frequency and intensity of MHWs in the GOT have never dropped, but have instead been more frequent, longer lasting and extreme than those metrics of MHWs between 1982 and 2009. Furthermore, the findings highlight significant changes in the SST over the GOT that may lead us to change or modify the reference period of the MHW definition. The findings also suggest that heat transport and redistribution mechanisms in the GOT sea are changing. This study contributes to our understanding of MHW features in the GOT and the implications for marine ecosystems. • A warming hiatus exhibited in the GOT during 1998-2009. • Annual mean and extreme hot SSTs are found a significant increase. • More frequent and longer lasting MHW over the GOT occurred after the warming hiatus. • Significant changes in sea surface temperature over the GOT suggest modifying the reference period of the MHW definition. [ABSTRACT FROM AUTHOR]