A mile wide asteroid is bad, but it's literally not the end of the world. In fact, impacting in the sparsely populated Pacific Ocean its immediate impact will be relatively minor compared to falling in a densely populated area.
To put this in perspective, the "dinosaur killer" at Chicxulub was about 6 miles wide, made a crater 110 miles wide, and had the energy of about 100 teratonnes of TNT.
Your asteroid is about on the scale of the one that created the 14 mile wide Haughton Impact Crater. This is still pretty big, but it's not extinction event bad. Because volume (and thus mass) is the cube of the diameter, your asteroid has 1/6th the diameter of the Chicxulub asteroid, but 1/216 the mass. That's still a lot, but it's not the end of the world.
Plugging the numbers into The Earth Impacts Effect Program tells the rest of the story...
- Energy before atmospheric entry: 2.01 x 1021 Joules = 0.5 teratonnes of TNT.
- No major global changes (mass, axis, orbit...)
- About 1.5 miles3 of material is ejected into the atmosphere. Since most of it is water, not dust, this will avoid long term atmospheric cooling effects, but it might destroy a large quantity of ozone leading to a UV spike.
- At 100 km everything is on fire or collapsed from the shockwave.
- At 200 km and 300 km everything is still on fire, many buildings collapse from the shockwave and seismic effects, most trees down.
- Finally at 400 km people will be relatively safe.
The impact will have the seismic effect of a magnitude 8.4 earthquake. By comparison the 2011 Tōhoku earthquake which caused the Fukushima meltdown was a 9.0 earthquake (much more powerful, it's not a linear scale) and sent a tsunami and surge over 100 miles. However, anything close enough to be affected by a resulting tsunami will be well inside the heat and shockwave. @YoustayIgo found an updated calculator which included tsunami calculations, boy was I wrong.
The asteroid impact hitting the ocean will shove aside so much water it will create an enormous tsunami. At 400 km from the impact, where you're likely to survive the heat and shock, the tsunami will arrive 40 minutes later with a maximum height of 150 meters. At 1000 km it's at 60 meters. At 2000 km it's still a towering 30 meters. Tsunami height drops linearly with the distance, so at 4000 km it's still 15 meters. At 6400 km, the distance from Tokyo to Hawaii, it's 9 meters similar to the wave heights experienced after the 2011 Tōhoku earthquake (the one that caused the Fukushima meltdown). The good news is you have 10 hours of warning after the impact. The bad news is it hits the entire Pacific Rim.
The good news is since the Pacific Ocean is sparsely populated, few people will be affected by initial impact. If the point of impact can be calculated, they can be evacuated.
The bad news is the whole Pacific coastline is flooded. Everyone, and as much of their stuff as possible, will have to be evacuated away from the Pacific coast to high ground. Like, far away. It will be a refugee problem on the scale never seen before. Major cities such as San Francisco and Los Angeles will need to be evacuated and their tens of millions of people cared for. The people of major island nations such as Japan, Taiwan, and Indonesia may have no where to go. Governments will have to stockpile food, water, shelter, and sanitation facilities at a scale never seen before.
The good news is all that water will recede rapidly. The bad news is all infrastructure, bridges, roads, power lines, sewage, buildings, fuel stations... will be trashed leaving the Pacific Coast uninhabitable by modern humans.
When they start to rebuild, they will find a major environmental disaster. All the toxic chemicals of modern life we leave lying around in pools or sealed in storage will now be released and smeared over the countryside. Nuclear material; all sorts of toxic chemicals; heavy metals; petroleum products like oil, fuel and asphalt. Governments will have to do their best to remove as much as possible in the months before the event, but much was never made to be transported. They will not get them all.
The world will be left with a refugee crisis on a scale they have never seen, and some of the most fertile and productive land in the world now a toxic wreck. The loss of food and economic production would put the world into a depression exacerbating the refugee crisis. Millions will die of starvation, disease, and exposure. The question now is how the world reacts to this, and how they rebuild.