Permeation Index: TDA Forecast Division Expects More 'Clear-Pattern' Days in November
The TDA Forecast Division released its long-range outlook for November's permeation index on the 1st. In most years, autumn's drier air tends to bring more 'clear-pattern' days with stable observing conditions, and this year is expected to follow the same trend. The division was careful to add, as always, that more clear-pattern days speak to ease of observation, not to any rise in how often the phenomenon itself occurs.
The TDA Forecast Division released its long-range outlook for November's permeation index on the 1st. What the division calls a "clear pattern" is shorthand for conditions with low atmospheric moisture, which reduces equipment noise and makes early signs of a Yuragi easier to detect — it has no direct relation to actual weather. In most years, humid summer months see more "cloudy-pattern" days, with the share of "clear-pattern" days rising as the air dries through autumn and winter. The long-range outlook released on the 1st projects a slightly above-average number of clear-pattern observation days in November, mainly around the bay area and the East Ward.
A division official reiterated, "This has nothing to do with the permeation index's actual level, or with how often a Yuragi actually occurs. It's purely about how easy it is to observe one when it happens." The clear footage captured by patrol-boat crew member Jo Kubota, 38, off Wakasu, previously reported on October 26, involved a non-recurring Yuragi — a one-off, unpredictable event — and the division said that falls into a different category from seasonal patterns. While acknowledging that such clear recordings could become somewhat more frequent during periods of higher seasonal observing precision, the division stopped short of drawing a firm conclusion.
The five stable windows, each monitored continuously by fixed equipment, are seen as largely unaffected by seasonal patterns. "A stable window's equipment is always pointed the right way, so it isn't much swayed by weather," the division explained. "It's really the precision of observing a non-recurring Yuragi — one that could happen anywhere, at any time — that the season's pattern affects."
