Is Tuesday Clearer Than Sunday? Day-of-Week Visibility (47,000 Obs)
2026-03-16
Aggregating 47,000+ visibility observations by day of week, Tuesday tops at 13.9m while Sunday and Saturday bottom at 13.1m. The 0.8m gap is small but consistent. Is this real — are weekdays actually clearer? Or is it reporting bias?
Visibility by Day of Week
Top 5 Sites with Largest Weekday Advantage
| Site | Weekday | Weekend | Gap |
|---|---|---|---|
| Tajiri | 9.6m | 8.9m | +0.7m |
| Kerama | 19.5m | 19m | +0.5m |
| Shirahama | 15.1m | 14.6m | +0.5m |
| Ishigaki | 20.6m | 20.1m | +0.5m |
| Mikomoto | 12.5m | 12m | +0.5m |
Three Hypotheses
Hypothesis 1: Weather Selection Bias (Most Likely)
Weekday divers (pros, guides, retirees) can choose good-weather days. Weekend divers go when they're free, regardless of conditions. This skews weekday data toward better conditions.
Hypothesis 2: Diver Density Effect
Weekend crowds may stir up sand with more fin kicks, slightly reducing visibility. However, this effect seems too small to explain the full 0.8m gap.
Hypothesis 3: Reporting Bias
Weekends are busy — shops may estimate visibility roughly. Weekdays allow more careful observation. Data quality differences could contribute to the 0.8m gap.
Conclusion
The 0.8m gap isn't perceptible in practice and shouldn't change your dive planning. However, taking a weekday off gives you more weather flexibility, which is the real advantage. This matters most at Tajiri (+0.7m) and Kerama (+0.5m).
About the Data
47,186 observations aggregated by day of week. Weekend (15,859) vs weekday (31,327) — both have ample sample sizes.
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