Buried by the Sky
Lucky souls who survived the Great Cataclysm remember a swift wind, colored black with uplifted earth, covering the ground with tens of meters of dust. Entire villages were buried; in the night, billions suffocated in their homes. Unlucky ones woke up to realize that they would soon be dead, as all their exits had been blocked by a killing storm, and tons of dust lay on top of them.
Those who were lucky enough to face the cataclysm and survive were devastated by the widespread destruction. Within minutes, their world turned alien; roads, cars, houses, and trees lay hidden under the burial drift. Soft earth and gravel, tree trunks, boulders, and walls summarily torn from their foundation and hurled thousands of miles away... Most of those who could not escape to the higher floors of multistory buildings and skyscrapers were asphyxiated or killed by the flying debris. The apocalypse lasted mere minutes. On the impacted hemisphere, over 99% of the population perished.
Beyond the assaulted hemisphere, there was no significant falling debris; only a forceful shockwave barely weakened by the gravity that pulled down the debris. Regardless of weather conditions, the shockwave formed a circular torrent of air that blasted across the globe like a nova, destroying a whole hemisphere in four hours, at speeds approaching 1500 mph.
You may think that no one survived, but you'd be wrong - the conservative estimate is that up to 5% of the population survived. Some took advantage of wind barriers - the shockwave only went one way out, from the epicenter. Some found underground shelters quickly enough, and were shielded from the power of the winds. The havoc of the shockwave was seen on television - after all, the geostationary sattelites were not affected. However, many survivors would attest that they spent but moments surveying the screen before deciding to search for shelter.
As over 70% of the Earth is covered by water, it is not surprising that the meteorite fell in an ocean - somewhere in the Pacific, in fact. Nevertheless, the consequences of a 'wall of water' never materialized as important. The immense size of the asteroid meant it caused much more damage through collision with terra firma. Preceeded by a wave of water, this "wave of fire and brimstone" erupted throughout the sky within a hundred kilometers of the epicenter. It was heralded by some Christian preachers as being the Armageddon come at last, to punish America for its sins.
Temperatures reached hundreds of thousands of degrees Celsius; all life in path of the firestorm was summarily obliterated. In the wake of this furiously destructive firepower, the water wave met the firestorm and readily evaporated; an ever increasing circle of white steam-cloud rose to the surface. In some places, the ground would take over a year to cool down completely.
On the first days, the extend of the damage was obscured from our satellites by dust and steam-clouds. Spectroscopic analysis revealed a charred terrain, featuring coloured splatches of tinted crystalline formations, like that of rose windows, as concentrations of impurities of various elements in a sea of glass that covered the seafloor in much the same way that grass covers a landscape. Former gamers who had once played Starcraft compared this to "Protoss Skyblasting". However, the true extent of the devastation was far less widespread in the wake of the collision.
The asteroid broke into several smaller pieces that burst up into the troposphere then came cascading down in a rough circle around the impact site. It looked like the mushrooms of a fairy ring. There they stayed, immense rising mounts of extraterrestrial material in a much larger ocean, breaking the surface of the water. These islands, nicknamed "Armagedda" by survivors, formed a new archipelago.
Sphere Culmination Effect
When the Earth was hit, shockwaves of wind spread in every direction, forming a ring that expanded from the epicenter. Eight hours after impact, the shockwaves would meet in a single point, on the opposide side of the planet. This is the Sphere Culmination Effect. Hours before the Cataclysm, head politicians and wealthy people had gotten on emergency flights, trying to escape. They were taken by surprise when the winds culminated, demonstrating a wrath that dwarfed even the Shockwave. Fortunately, it was far more limited in scope.
The collision of the winds caused a stall, that quickly became physically impossible to sustain as more and more air was focused in a few dozens of cubic kilometers. Abruptly, the pressured gases exploded, generating a second crater that pummeled hundreds of meters into the ground. The remaining pressure was relieved upward, rocketing into the vast stretches of space. All the VIP's gasped as a circular aurora reappeared again and again higher and higher into the air in this tropical location. The circular patterns of hyperdense cloud cover, aurora, crater, and crop circle was a stunning sight, but altogether, it was not worth the billions of lives that were lost.
The Sea Rises
The sheer amount of debris tossed onto the planet caused a tremendous amount of water to be displaced. All coastal regions were submerged, and with them were destroyed most human settlements. A new landmass arose in the middle of the Pacific, near the epicenter of the strike.
The sudden rise in global water levels caused a significant amount of destruction that could not be understated. The only settlements that were spared were located at higher altitudes. The increased water coverage of the earth resulted in increased evaporation; the cloud cover had become twice as big as it was before the cataclysm. Rain became more frequent than ever before; and in the beginning, it was dark and acidic, also being filled with dust.