Recent forecast models from the Japan Meteorological Agency and global ensembles show a strengthening high-pressure ridge over eastern Japan, driving southerly flow that is elevating maximum temperatures above the late-spring climatological average of 23–25 °C. Ensemble guidance now clusters around 27–29 °C for May 18, with limited spread among leading runs, supporting the 55.5 % market-implied probability for 28 °C or higher. Persistent clear skies and minimal cloud cover have further amplified daytime heating, while the absence of a significant frontal passage keeps the warming trend intact through the short-term horizon. Updated model cycles in the next 24–48 hours remain the primary catalyst that could shift these odds before resolution.