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 have 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 have heavy rains during the winter months, and Wednesday's were unusually strong, swamping Jiddah with 70mm 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 35km 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 three 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' Centres 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 affect H1N1. We can't predict," he told The Associated Press.
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.
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 kilometres apart. In Mecca, they rushed around puddles for shelter under concrete overhangs.
During the rainy months of November through January, heavy downpours often swamp neighbourhoods 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.
On Thursday, the massive crowds 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.