Evening humid-heat maxima near the southern Persian/Arabian Gulf

Extreme humid heat is a major climate hazard for the coastal Arabian Peninsula. However, many of its characteristics, including diurnal and spatial variations, remain incompletely explored. Here we present evidence from multiple reanalysis and in situ datasets that evening or nighttime daily maxima in extreme wet-bulb temperature and heat index are widespread along the southern Persian/Arabian Gulf coastline and adjacent inland desert, driven principally by sea-breeze-related movements of moist maritime air. This timing runs counter to the general expectation of more intense heat and greater heat-stress risk during daytime hours. While wet-bulb temperature is one of many metrics relevant for understanding heat hazards, it has featured prominently in recent literature and its values are closer to uncompensable-heat limits in coastal Arabia than anywhere else. Deviations from an afternoon-peak assumption about heat risks are thus of critical importance and heighten the value of improved understanding of extreme-humid-heat meteorology, in this region and in others subject to similar physical processes.