The overthrow of the Khartoum regime, said the NDA, would be precipitated by an intifada (uprising), accompanied by the mutiny of a large part of the armed forces. The regime of President Omar Hassan al-Bashir may collapse by the middle of next month, they say.
These predictions follow last week's issuing of an NDA ultimatum to the government to step down peacefully. The NDA's members include the two leading opposition parties, the Umma (Nation) Party and the Democratic Unionist Party, as well as the Sudan People's Liberation Army (SPLA), which has been fighting the forceful imposition of Islam on the southern part of the country since 1983.
"We plan to ignite a popular uprising in a dozen towns and cities across northern Sudan," said Omar Nureldayem, secretary of the Umma Party and a former finance minister. "We don't expect a government capitulation but we do believe there will be military support for the uprising."
Dissatisfaction has been growing with the military junta of General Bashir, which is inspired by the National Islamic Front (NIF) of the ideologue, Hassan al-Turabi. The costly effects of the war, human- rights abuses and crippling price rises have caused hardship and suffering in the Arab north.
From abroad, there has been mounting criticism of Khartoum, which is accused of sponsoring international terrorism.
In April, the UN imposed diplomatic and travel sanctions on Khartoum for its failure to hand over suspects wanted in connection with last year's attempted assassination of Egypt's President, Hosni Mubarak.
"The time is now ripe for an uprising in Sudan", said Dr Nureldayem who, with other members of the NDA's opposition-in-exile, is based in the Eritrean capital, Asmara. "There will be casualties - perhaps a few thousand people will die. But the intervention of the army would considerably reduce the bloodshed."
Protests against price rises have been brutally suppressed by the government. The NDA predicts that increases in the price of fuel and other commodities will impel large sections of the populace to take to the streets.
"It is our intention that the Khartoum regime be overthrown from inside Sudan," said General Fathi Ali, a former commander of the Sudanese navy and now military head of the NDA based in Asmara.
"We expect the NIF government will try to suppress the planned demonstrations. But more than 90 per cent of the Sudanese army is on our side and there will be a mutiny if the government uses force. The uprising will take several days to build up. Within a week to 10 days we will have secured the overthrow of the regime."
General Ali, a graduate of Camberley army staff college, said he could muster a "small but capable armed force" to advance on Khartoum from the Eritrean border region.
Eritrea broke diplomatic ties with Sudan a year and a half ago, over Khartoum's support of Eritrean Jihad, a small force of exiled Eritreans committed to the overthrow of the secular government of President Issaias Afewerki. Since then Eritrea has provided military training for the Sudanese opposition.
"The Sudanese allied forces can be counted in their hundreds," said a Western diplomat in Asmara. "There are guerrilla bands operating out of a number of bases in Eritrea. Militarily, they're like mosquito bites but psychologically they're very important. The opposition has the potential to seriously harass Khartoum. It has forced the Sudanese army to move resources from southern Sudan and deploy significant units in the north-eastern region."
The Eritreans, who recently celebrated the fifth anniversary of their successful struggle for independence from Ethiopia, are regarded as having produced one of the most capable guerrilla forces in African history.
Eritrea has been unable to dissuade Khartoum from attempts to export Islamic fundamentalism. In recent months there has been an increase in Eritrean Jihad raids into Eritrea from Sudan and the two countries' border region is described as extremely tense.
"We realise there is no possibility of making Khartoum change its mind", said the Eritrean Foreign Minister, Petros Solomon. "It has shown a very clear intention to destroy our government. We have no alternative but to resist and to help the alternative Sudanese political parties press for a change in Khartoum".