Current forecasts from the Japan Meteorological Agency place Tokyo’s overnight minimum for May 18 in the 17–19 °C range, matching the closely bunched market probabilities. Mid-May climatology shows typical nighttime lows of 15–18 °C under transitional spring conditions, where clear skies allow radiative cooling while a strengthening Pacific high limits cold-air intrusions. Minor model spread arises from uncertainty in cloud cover and any weak frontal passages across the Kanto Plain, which could nudge the low a degree lower or sustain warmer southerly flow. Ensemble guidance released in the past 48 hours has kept the central tendency stable near 18 °C, with only modest day-to-day revisions expected before the 18th.