What would happen if a 10Km astroid hit the Pacific ocean tomorrow at 5 O'clock GMT?

a tsunami would engulf the ocean and would build up until they hit the shores of the eastern usa it would instantly flood manhattan rhode island and other citys it would cause devestation and kill hundreds or even thousands

You can simulate it's effect on your current location with the Earth Impact Effects Program.

It does not calculate Tsunamis yet, as they depend largely on the coast they hit, but the remaining effects should already be annoying enough.

It will not be the end of the world, at least not for all humans. For some many it will.

We would all be frozen to death in a matter of days. Those lucky enough to still have bomb shelters might live a few more weeks, but they would starve to death from lack of food. It would take a minimum of 3-5 years for the earth to be inhabitable and start growing food again. The only survivors would be the same creatures that survived the meteor that destroyed the dinosaurs. Roaches.

I would, presumably, need to get a haircut.

Surfer dudes on the California and Hawaii beaches would be yelling "Surf's Up! Surf's REALLY UP! OH MY GOD, IS THE SURF EVER UP!!!!"

Shortly after that, mile high tsunamis would begin striking the coastal areas of the Pacific basin. The tsunamis would propagate into all the other oceans. Anyone less than half a mile above sea level and within 25 miles of the oceans would vote that it was about to be the worst day of their lives. Within an hour of the strike, molten and extremely hot rock would be showering down all over the planet, starting forest fires that will burn for months. The temperature of the atmosphere would rise to levels sufficient to kill any unprotected plant and animal. Most land dwelling animals would become extinct within days. Humans would die by the billions. The survivors would face decades of survival mode living, followed by centuries of agrarian living and attempts to save the knowledge and technology that makes our lives so simple today, compared to those of people even 100 years ago.