Cloud and rain could upset the viewing plans of thousands of eclipse watchers across the State particularly in the west, according to Met Eireann.
The latest forecast shows a belt of rain moving in from the Atlantic around the time the effects of the eclipse can be seen between 10 a.m. and 12.30 p.m. on Wednesday.
Depending on how fast this rain belt moves, the event could be a washout in the west and other parts of the State.
Mr John Doyle, meteorologist with Met Eireann, said yesterday the south-east may offer the clearest views of what, for those watching in the State and Northern Ireland, will only be a partial eclipse.
If the weather is clear, Cork and Kerry are expected to offer the most dramatic view. "Weather-wise the south-east will be the best spot as it is close enough to the totality path and furthest away from the approaching rainbelt . . . but timing is critical and visibility will depend on how fast or slow the cloud moves," he said. "The cloud may be thin enough not to completely obscure the sun's disc, especially over Leinster and east Munster."
Further west and north, he added, the cloud could be thick enough to produce rain and drizzle.
The total eclipse of the sun by the moon will occur for 21/2 minutes at 11.11 a.m. on Wednesday, in the path of totality, a small area of the earth which in Europe straddles Cornwall in England, Stuttgart in Germany, northern France, some of Belgium, Luxembourg, Austria, Hungary and Bulgaria.
For the millions expected to travel to locations in Britain and France within the totality belt, the outlook is only slightly better according to Mr Doyle. In Cornwall, cloud will be increasing from the west but should be thin enough to see a little of what is happening. The weather in Cherbourg, France, will be similar, he said, and conditions should be smooth for those people watching the eclipse from aboard seacraft.
At home, an astronomy club has organised eclipse viewings in 15 locations. The Astronomy Ireland events will take place at churches, community centres and parks. Special "eclipse shades", which the association says are proven to provide protection from the sun, will be available at each centre.
Astronomy Ireland president Mr Dave Moore says "there is no point travelling any further than your nearest Astronomy Ireland event to see the eclipse". Weather permitting, a "crescent sun" will be visible all over the country as the moon moves in front of the sun. There will be more coverage, up to 97 per cent, in the south but, according to Mr Moore, it is not worth a long journey just to see a slightly thinner crescent.
The eclipse is not total anywhere over Ireland and there has not been a total eclipse over the State since 1724. The next time one will occur is 2090.
A total eclipse occurs when the moon passes over the sun covering it and momentarily casting everything in shadow. Those in the path of totality on Wednesday will see the morning sky turn to night and the stars and planets become visible.
A partial eclipse is where the sun is only partly obscured by the moon. This time the northern parts of Donegal and Derry will experience 85 per cent coverage of the sun, while a much deeper eclipse, with around 97 per cent coverage, is expected on the southernmost tip of the Island.
According to Mr Moore, on average there is a total eclipse of the sun every 18 months somewhere in the world, "but if you stood still on the earth you would only see one every 400 years". Dublin is statistically one of the least likely places to experience a total eclipse. The last one took place in 1652 and the next total eclipse is not due over the capital until 2600.
For more information on Eclipse Watches, call the Astronomy Ire- land information line, 1550 11 11 30 (calls cost 58p per minute), or access their website on www.astronomy.ie