Recent Hong Kong Observatory guidance and international ensemble models indicate daytime maxima clustering near the May climatological average of 28–29 °C for the 19th, driven by a weak subtropical ridge that limits strong heating while allowing modest boundary-layer warming under partly cloudy skies. Variable easterly flow and scattered showers introduce the key uncertainty separating these two leading outcomes, as increased moisture and cloud cover can suppress peaks by 1–2 °C relative to clearer intervals. Historical records show mid-May highs averaging 28–31 °C under similar synoptic patterns, with small differences in forecast timing of convection or wind speed explaining the market’s tight split between 28 °C and 29 °C. Updated model runs and the Observatory’s next briefing will provide the next clear signals for traders.