A Summary of Weather Prospects for the 10 June Annular Eclipse

With only three areas to chose from in which to see the eclipse, the discussion of weather prospects is greatly simplified. The global map of mean monthly cloudiness for June leaves little doubt as to the most promising area - the region just south of the Baja Peninsula in Mexico. Cloud cover here averages just under 20% for the month compared to 50 to 70% on the sunrise side of the track. Unfortunately the only access to this location is by boat.

The favourable circumstances around the Baja Peninsula do not extend into mainland Mexico. The region south of Puerto Vallarta where the sunset eclipse makes landfall has a much greater cloudiness, though sunnier than the opposing choices in Indonesia and Taipan.

Indonesia

June comes between the wet and dry seasons and so the cloud cover prospects lie between the best and the worst that this tropical climate can offer. At Manado, the closest site to the track, the frequency of clear or scattered cloud at eclipse time is around 50%, much better than February's 25% but short of September's 63%. The case for an Indonesian eclipse site is further improved by noting that the weather is very convective in June, with the result that cloudiness and rain is more likely in the afternoon than during this morning eclipse. About 9% of the observations at 7AM have rain mentioned, in comparison to those at 1PM where over 40% show precipitation. Overall, as can be seen in Table 1, thirteen of 30 days in the month have a measurable fall of rain.

Fog is relatively common, especially in the morning hours where one day in ten has a reduction in visibility. Tropical days also tend to be hazy, partly from the high moisture levels in the air and partly from smoke.

From Indonesia the eclipse track is most accessible from Sulawesi, where it begins at sunrise. Farther northeast the track crosses several islands in the Kepulauan Sangihe and Kepulauan Talaud. These islands must be reached by boat from Manado; the crossing takes 12 hours to reach Tahuna on Sangihe Island and 20 to reach Beo on Talaud. Sangihe has a well-developed infrastructure with good hotels and roads. The capital Tahuna is the hub for travelling around the island and lies a little north of the centre line. Most foreign visitors come for bird watching or diving. Talaud is more remote and less developed but the ferries stop at Beo on Karakelong Island, which also lies just a short distance north of the centre line.

Tinian and Saipan

In contrast to the season in Indonesia, June comes at the end of the dry weather season in the Marianas Islands. The percent of observations reporting rain at eclipse time is down to only 9% though the frequency of skies with no or scattered cloud is very nearly the same as in Manado. A look at the three sites on Guam in Table 1 shows small differences in cloud frequency, most likely due to the surrounding terrain and its influence on the formation of cloud. Wind blowing uphill will tend to form cloud while those on the downslope side will tend to erode it. Eclipse observers should attempt to take advantage of whatever terrain is available and place themselves in one of two spots if the weather is active:

• Set up in the lee of higher hills and as far downrange as possible. The eclipse track and the shape of the islands suggests that this is only an option on Tinian, and there only barely, as the island is relatively flat (the highest point is only 186 metres above the waterline). While the terrain on Saipan is higher, the north limit skips across the southern part of the island and misses the bigger peaks. The intent is to be in an area of downslope flow, but winds often form eddies around small islands and can curl onshore from an unexpected quarter so care must be taken to observe the wind and clouds beforehand, at the approximate time of the eclipse.

• Set up on the windward beaches where the influence of the island on the onshore winds is at a minimum. This is probably the preferred location but means that the observing site will be exposed to the full force of the trade winds. On Saipan the north limit crosses Magicienne Bay and the trade winds likely diverge from their steadily easterly direction to curl into the Bay. The main advantage of a windward site is to avoid any clouds that might develop over the land as a consequence of solar heating.

Of the three general locations to watch the eclipse, Tinian or Saipan may be the easiest (though not the quickest) to reach. With good connections to the outside world, a small size, and a modern infrastructure, reaching the eclipse track should be relatively easy. The main limitation is that the centre line is not accessible except by boat, though the southern tip of Tinian, Puntan Carolinas, reaches about 60% of the way (within 9 km). Tinian and Saipan's appeal probably lies mostly with the ability to easily view the eclipse from the north limit where Baily's beads will be more extensive and continuous. On Tinian, the north limit will be very close to Old North Field, the WWII airfield from which the Enola Gay departed for Japan with its atomic bomb. The field is largely deserted and can be used as a site from which to view the eclipse if its location is suitable.

On Saipan the eclipse limit lies barely north of the airport, making for a very short commute indeed for those in a hurry. The track lies south of the highest peak on the island, 472-meter Mount Tapochau. This peak will offer little protection to the eclipse track as the prevailing winds are from the east. Given the shape of the island, observers should head for a site on the west side of Magicienne Bay (Laulau Beach) or near Kagman Point. The airflow into Magicienne Bay could be very complex and cloud patterns should be watched closely ahead of the eclipse. On the balance however, these islands are so small that weather need only be avoided by looking around and heading for the best spot.

Mexico

Mexico is likely to be the favorite spot from which to observe the eclipse in spite of the Sun's low altitude (or perhaps because of it). I've already noted that the waters off of the south tip of Baja offer by far the best weather prospects. Otherwise eclipse-chasers will have to travel a modest distance south of Puerto Vallarta to reach the annular track. It's not a difficult journey - there are many resorts along the way and a smattering of small coastal villages to provide a "get away from it all" experience. First the weather…

June is the first month of the wet season. Rain is reported on ten days of the month on average, but seems to be more an evening and night-time event - about 2% of the 4PM observations at Puerto Vallarta have rain versus 9% at 10 PM. There is a corresponding change in cloud cover: at eclipse time about 15% of skies are overcast compared to over 50% at 10 PM. Nevertheless, the frequency of clear and scattered conditions at eclipse time is almost identical to those in Indonesia and Saipan (Table 1). Table 2 shows some weather statistics from climate stations around the state of Jalisco but there is little difference from one site to another.

The map of the Mexican part of the eclipse track shows a number of small villages within the zone of annularity. It must be noted however that this is very rugged terrain with dense forests - conditions that do not generally lead to an unobstructed view of the sunset horizon. It would seem that the beaches are the first places to head for, though scouting will almost certainly find numerous westward-facing slopes with a good view out to sunset. And while the mountains themselves are rugged and short on westerly horizon views, the coastal flats are occasionally quite extensive and the setting sun can be seen from a considerable distance inland. Still, a water horizon offers an opportunity to see a green flash as a very narrow crescent sun sets in the west. Indeed, the most attractive part of this event may not be the eclipse itself but the setting crescent.

The road from Ipala southward would seem to offer a continuous waterfront view, as does a site at Aquiles Serdán. The latter is reached by a 37 km road from Highway 200; visitors will find themselves to be a local curiosity. Aquiles Serdán is separated from the beach by a narrow lagoon which must be crossed by boat if a waterfront vantage point is wanted (but be cautious - a crashing surf may cast salty spray into the air to descend on telescope optics). Travellers should expect to use a capable four-wheel drive vehicle to reach this hamlet or any others off of the main highway. Just before Aquiles Serdán vehicles must ford the Rio Tecolotlán (or passengers may walk across to the village). Care must be taken in following the roads shown in the map of the track as the it does not show all of the routes.

For the less adventuresome, Ipala and its environs offer the best sites for a view of the eclipse and the seaside road promises at least a modest chance at movement to avoid an errant cloud at eclipse time. Ipala is 47 km from El Tuito and is the supply headquarters for occasional tourist looking for fishing, beachcombing, surfing and camping. It lies on the open ocean and will provide an unobstructed view of the setting sun (except for clouds of course). South from Ipala the road gets rougher and then improves, passing several small hamlets on the way to La Cruz de Loreto. For those determined to be on the centre line, this may be the only approach unless a open horizon can be found at Gargantillo.

If you find yourself wishing for a little more comfort, La Cruz de Loreto boasts the luxury Hotelito Desconocido (www.hotelito.com) from where the eclipse will be readily visible across white beaches. Rates range from $234 to $528 per person per day (plus taxes) and a reservation is recommended.