CAPE CANAVERAL, Fla. — Everything is on track for Friday’s launch of the space shuttle Endeavour, with President Barack Obama, U.S. Rep. Gabrielle Giffords, and as many as 700,000 onlookers along the Space Coast on hand to cheer its final mission.

But weather could disappoint everyone.

Shuttle weather officer Kathy Winters said Thursday that the prospects of crosswinds and cloud cover Friday afternoon have increased the probability of a weather-delayed launch to 30 percent, up from the 20 percent prediction NASA has been holding much of the week.

The storm front that devastated Alabama and other southern states Wednesday night is likely to pass through Kennedy Space Center Thursday night but it is not expected to cause severe weather here and should be gone by midnight, she said. So it should have no effect on Friday’s weather-sensitive activities, which begin with filling the rocket’s external fuel tank.

The launch is slated for 3:47 p.m. EDT. The Obama family and Giffords, the Arizona Democrat critically wounded in the Tucson shooting in January, are planning to be at Kennedy for the launch, along with scores of other VIPs. Giffords’ husband, Navy Capt. Mark Kelly, is Endeavour’s commander.

Winters said she would not be surprised if there were weather alerts raised during the day on Friday, but conditions should improve, and by late afternoon and should be fine for launch.

“”Our big concerns are crosswinds and (low cloud) ceilings lingering in the area,”” Winters said.

Also lingering in the area Friday: hundreds of thousands of shuttle watchers. NASA test director Jeff Spaulding, who oversees the countdown, said the estimates cited earlier of 45,000 people at Kennedy Space Center and 700,000 in Brevard County were probably good.

He said he expects “”an incredible crowd.””

Those spectators — and special attention and security for the Obamas and Giffords — should not affect preparations, the countdown, or any decisions relating to whether weather or other factors might cause a scrubbed launch, he said.

However, if for some reason the shuttle launch is scrubbed, the traffic mess along the space coast could cause NASA to consider waiting two days, instead of one, before trying again, he said.

Currently, the next launch target after Friday is Saturday, at 3:22 p.m. EDT. But Spaulding said he was worried about getting shuttle workers home and back with ample rest time in between attempts, and a 48-hour delay might be considered. On Sunday, the launch target would be 2:59 p.m. EDT.