(FOX News) JIDDAH, Saudi Arabia — The heaviest rain to hit Islam's annual hajj pilgrimage in years soaked the faithful and flooded the road to Mecca, snarling traffic as millions of Muslims headed for the holy sites. The downpours add an extra hazard on top of intense concerns about the spread of swine flu.
Pilgrims in white robes holding umbrellas, some wearing face masks for fear of the flu, circled the black cube-shaped Kaaba in Mecca, the opening rite for the hajj.
But the shrine — Islam's holiest site — and the nearby, rain-soaked streets did not see the usual massive, pushing crowds, because many tried to stay inside nearby hotels or were caught in the traffic jams heading into the city.
Mecca and the nearby Red Sea coastal city of Jiddah often see heavy rains during the winter months, and Wednesday's were unusually strong, swamping Jiddah with 2.76 inches of rain, more than it gets in a year on average, according to weather officials.
They were the heaviest in years to coincide with the four-day hajj. Already jammed traffic was worsened — with a jam of cars as long as 20 miles on the partially closed road from Jiddah to Mecca, and some pilgrims and journalists were trapped in Jiddah.
The rains could also exacerbate the hajj's perennial dangers. The rites — a lifetime dream for Muslims, who come to cleanse their sins — are always a logistical nightmare, as a population the size of a small city moves between Mecca and holy sites in the nearby desert over the course of four days.
In the past, the rites have been plagued by deadly crushes caused by congestion as the unimaginable crowds perform the rituals. In 2006, all it took was a piece of luggage dropped by one person to trip up others and cause a pile-up that killed more than 360 people.
A slippery, rain-slicked street could be equally deadly — and with the main rites due to begin outside Mecca on Thursday, Saudi authorities urged those arriving at the holy sites to move cautiously and not to rush.
This year has brought the added worry that the massing of more than 3 million people from around the world could bring a swine flu outbreak. In the past months, the Saudi government has been working with the United States' Centers for Disease Control and Prevention to set up clinics and precautionary measures to stem any outbreak.
Shahul Ebrahim, a consultant from the Atlanta, Georgia-based CDC at the hajj, said it was too early to tell if the rains could exacerbate the spread of H1N1, which is transmitted in the air, not by water.
"Rain can lead to other waterborne diseases ... But we still don't know how it will effect H1N1. We can't predict," he told The Associated Press.
Hassan El Bushra, an epidemiologist in the Cairo office of the World Health Organization, said "there is no evidence that this will cause any kind of spread, including the spread of swine flu." It could even be beneficial if it means crowds are smaller, he said.
So far, four pilgrims have died from the H1N1 virus since arriving in Saudi Arabia in recent days, and 67 others have been diagnosed with the virus, Saudi Health Minister Abdullah al-Rabeeah told the Arab news network Al-Jazeera English.
Signs at the airport and around the holy sites urge the faithful to cover their faces when they cough, wash their hands often and wear a mask. The swine flu vaccine is given free at the airport for those who want it. More than 100 clinics have been set up at holy sites, and large supplies of Tamiflu and other anti-flu medications are on hand.
The crowds provide a perfect environment for swine flu's spread, said Ebrahim. "We are expecting there to be seven people standing in one square meter at any given time during prayers, and this is very dangerous for airborne diseases like swine flu," he said.
"There is no personal space," he said. "Ideally you should be one meter away from someone to avoid catching the disease."
So far, traffic jams were the worst result from the rains, as pilgrims in convoys and on foot struggled to get to some of the sites, which are miles apart. In Mecca, they rushed around puddles for shelter under concrete overhangs.
During the rainy months of November through January, heavy downpours often swamp neighborhoods in Mecca and Jiddah because of poor drainage.
Moreover, Mecca is deep in a mountainous desert valley, so even a short, intense rain can cause dangerous flash flooding. Over the centuries, the Kaaba has had to be repaired several times because of damage from flooding.
The hajj occurs according to Islam's lunar calendar, so it rotates through the year. Since 2004, when it has taken place during the rainy winter months, it hasn't been hit by storms heavy enough to hamper the rites.
For about two decades before that, it took place in blazing summer months in which no rains fall. One Saudi in his 30s on Wednesday said he couldn't remember such hajj rains in his lifetime.
Civil Defense spokesman Maj. Abdullah al-Harthi said his organization has plans ready to deal with flooding, including 300 buses to evacuate people if necessary. He said no casualties have been reported from the rains, the official Saudi Press Agency reported.
One lane of the main road into Mecca was closed by flooding, reducing it to one lane, said Amer al-Amer, an Interior Ministry spokesman. "It cannot handle the pressure of all the people coming from outside Mecca," he said, adding that it would cause delays of several hours for people trying to reach the sites.
The crowds are expected to exceed last year, when some 3 million attended, al-Amer told AP.
Streets were flooded in Jiddah, the entry point for many coming for the rites. They were making their way to Mecca to perform the circling of the Kaaba and to the nearby desert valley of Mina, where a sprawling tent city has been set up for them to live in.
Water covered the floors in many of the tents, said Suleiman Hamad, a 29-year-old pilgrim in Mina. He said the scene was "muddy, but manageable," with many throwing blankets over their heads when they walked outside.
Rain fell sporadically throughout the day, and stopped by late afternoon in many sites — though it continued to fall in Mecca. Al-Amer and other authorities were optimistic that flooded areas would dry by evening.
On Thursday, the mass will flock to Mount Arafat, a plateau outside Mecca where the Prophet Muhammad delivered his farewell sermon. They then proceed to Mina, where over the next three days they perform a rite stoning three stone walls in a symbolic rejection of the devil.