Weather Summary

With all of these weather demons converging on Southeast Asia and the islands of Indonesia, the prospects for eclipse observing would seem to be quite dismal. Figure 8 shows that the mean cloudiness ranges from 60 to 80 percent through the area, four to five times higher than over western India. Figure 9 hints at the disadvantage of the close proximity of the ITCZ and its thunderstorm clusters. Table 16, derived from actual observations along the path, also provides a pessimistic outlook with a very low frequency of sunny skies. So what are the actual prospects for clear skies at eclipse time? The best statistic, unfortunately collected at only a few locations, is the actual number of hours of sunshine. Figure 10 promises between 7 and 10 hours at Indian sites. Phnom Penh and Kratie, both in Cambodia, average 6 hours per day in October, and Ho Chi Minh City (Saigon) reports 4.5 (Table 16).

By dividing the number of sunny hours by the number of hours between sunrise and sunset we can calculate the percent of possible sunshine for each site. Such a statistic allows the various locations along the track to be compared directly, and it provides a good estimate of the actual probability of seeing the eclipse except for morning/afternoon differences. It also corrects for the different lengths of the day at the various locations.

An eclipse site in Cambodia or Thailand would have about a 50% probability of seeing the eclipse, in Vietnam about 40%, and locations in western India 85 to 90%. Other values, where available, are given in Table 16. Mobility would normally raise the likelihood by a few percentage points for most eclipses, but the very narrow track for this eclipse limits the distance that can be explored for holes in the cloud. The advantage gained is probably not more than 5%.

One exception is for those who observe at sea where a ship is free to range along the track. Ships are limited by a relatively slow speed, but are not constrained by orographic barriers (islands, perhaps) or the need for roads. Knowing where to sail will be critical, so the advantage to be gained will be determined by forecast accuracy and lead time. There are many variables to consider, but a rough estimate might be that a shipboard chase would confer a 10% advantage.

Unfortunately, sunshine statistics are not available for Indonesian and Philippine islands along the track, and in any event land-based measurements do not accurately reflect conditions on the ocean. We are left with the need to accept substitutes, for which the cloud cover data of Figure 8 will have to suffice. A comparison between locations with similar cloud statistics forces the conclusion that sunshine hours on the South China Sea between Borneo and Vietnam are comparable to conditions at Ho Chi Minh City, and the Celebes Sea near Sulawesi is comparable to the sheltered interior of Cambodia and Thailand. Add 10% for mobility, and shipboard observers have a 50 to 60% probability of suitable skies for the shadow passage.

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