A lot of what happens depends on the amount of warning, and how solid the warning is.
If the warning is thought to be reliable intel there is a range of possibilities from a significant Japanese defeat to an utter disaster for the USN.
Scenario 1. Best case U.S. 7-8 Hours notice of the attack, no information on the position of the Kido Butai. Aircraft are on Dawn Patrol, probably close to a full squadron. Radar warning flushes the rest of the fighters (total of 12 A-20, 36 P-36, 99 P-40 (87 "B", 12 "C" models), 21 F4F, 8 F2A total of 164 fighters and 12 350 MPH attack bombers) while the PBY and bombers head out to sea in the opposite direction. All Army AAA is up and manned, ships in harbor have either gotten up steam or are at Condition One in port. 187 Japanese aircraft are hit by 164 American Fighters. Even with the great quality of the IJN pilots first wave loses close to half the strike force (probably 35 shot down, 60 or so mission killed). Second wave may be called off (it is already in the air), if it comes in, a significant percentage of the U.S. fighters will be on the ground rearming/refueling so this wave faces somewhere around 40-50 fighters, figure 35-40% loss (20 shot down, 50 mission killed) for a total of 90 aircrew and 155 aircraft. American aircraft losses are in the area of 30 shot down, 50-60 shot up. Pennsylvania get hit in the dry dock, maybe worse than IOTL, at lest one, possibly two of the BB get caught at anchor and eat torpedoes, Utah, thanks to her berthing site, get ripped to little bits. Four BB, several cruisers, and a number of destroyers sortie and head to the southwest toward the Mandates, which was the expected axis of any IJN attack on Hawaii which is the opposite direction from the actual IJN line of approach putting them out of range for the IJN aircraft.
Scenario 2. Good result U.S. 4 hours warning, no information on IJN position. Ships are able to set Condition One, Nevada, several cruisers (1 CA, 3-4 CL) 15-20 DD sortie and move toward Mandates. Army AAA 2/3 manned and with 50% or less ammo. ~40% of fighters get up at least partly armed. IJN first wave attack is disrupted, but not stopped completely. Attacks on airbases are only partly successful. Second wave finds Army AAA at 100% ships fully ready. IJN aircraft losses 10%, mission kill 20%-30% (105-140 aircraft). U.S. loses 100+ aircraft in air or on ground. Most BB take some damage, with at least one being a total loss (Oklahoma is a good bet, she's out board and has the worst internal compartmenting of the outboard ships).
Scenario 3. Draw 2 Hours warning, no information on IJN location. Most ships are at Condition One, Army AAA less than half manned with limited ammo, 20-30 fighters get up. Shipping losses are close to OTL, but with less damage to California & West Virginia thanks to less flooding but IJN aircraft losses are 10%, 15-20% mission kill (88 aircraft, 35 aircrew).
Scenario 4. OTL significant IJN tactical victory.
Scenario 5. Less favorable U.S. result U.S. 7-8 Hours notice of the attack, accurate information on the position of the Kido Butai. Aircraft are on Dawn Patrol, probably close to a full squadron. Three BB and some escorts head toward IJN and are caught in deep water with less than 15 fighters as CAP. All BB lost, at least one cruiser, all in deep water. Japanese force that continues to Pearl is savaged as in Scenario 1. American casualties are 3,000+.
Scenario 6 Strategic U.S. Defeat 12 Hours notice of the attack, accurate information on the position of the Kido Butai. Aircraft are on Dawn Patrol, probably close to a full squadron. Entire battle line heads out to engage IJN. Caught in open water by both IJN waves at edge of Fighter Cover. Five BB lost, two damaged in open water. Pearl facilities not struck, USAAF losses minimal. Japanese losses are under 30 aircraft. U.S. casualties 4,000+
Scenario 6 Utter U.S. Defeat 18 Hours notice of the attack, accurate information on the position of the Kido Butai. As in # 6 except Lexington TF moves into position to intercept. Lexington has 16 F2A Buffaloes for CAP/Raid escort against 6 Japanese carriers. Lexington lost, probably with one or two of CA escorts.
A couple notes:
The BB at Pearl had not received their planned 1940's upgrades (Colorado was not at Pearl because she was getting this major upgrade which included addition of 5"/38 DP guns). They had a 4 76mm AAA and some 1.1" pom-poms along with .50 cal machine guns for anti-aircraft. In port, tied up, they could put up a reasonable amount of small caliber flak into a small area. At sea, at normal formation spacing, they were almost helpless, something the the Navy had recognized from the early battle in the North Atlantic and was one of the main goals of the planned modernization.
The AAA at Pearl was fairly dense, for the time. It was totally inadequate for the attack at hand, especially in heavy flak. The 76MM guns topped out at 20k feet, something that was know to the IJN, with most of the remaining AAA being 20mm and .50 cal. It is likely that, in ideal conditions, the AAA would have taken down more no more than 10% of the enemy aircraft in each wave, with 5% being a much more likely (and quite good) outcome, with a similar number mission killed and pushed over the side when they returned to the carriers.
The Fleet was not up to handling the Kido Butai at sea, anything that creates that sort of engagement is a disaster. Although he wouldn't have done it, Kimmel's best play was to run to the southwest, collecting the Enterprise Group as he went. The USN was at least a solid year from having a surface force that could defend itself from a serious air attack, even with a carrier in support.
If the warning is thought to be reliable intel there is a range of possibilities from a significant Japanese defeat to an utter disaster for the USN.
Scenario 1. Best case U.S. 7-8 Hours notice of the attack, no information on the position of the Kido Butai. Aircraft are on Dawn Patrol, probably close to a full squadron. Radar warning flushes the rest of the fighters (total of 12 A-20, 36 P-36, 99 P-40 (87 "B", 12 "C" models), 21 F4F, 8 F2A total of 164 fighters and 12 350 MPH attack bombers) while the PBY and bombers head out to sea in the opposite direction. All Army AAA is up and manned, ships in harbor have either gotten up steam or are at Condition One in port. 187 Japanese aircraft are hit by 164 American Fighters. Even with the great quality of the IJN pilots first wave loses close to half the strike force (probably 35 shot down, 60 or so mission killed). Second wave may be called off (it is already in the air), if it comes in, a significant percentage of the U.S. fighters will be on the ground rearming/refueling so this wave faces somewhere around 40-50 fighters, figure 35-40% loss (20 shot down, 50 mission killed) for a total of 90 aircrew and 155 aircraft. American aircraft losses are in the area of 30 shot down, 50-60 shot up. Pennsylvania get hit in the dry dock, maybe worse than IOTL, at lest one, possibly two of the BB get caught at anchor and eat torpedoes, Utah, thanks to her berthing site, get ripped to little bits. Four BB, several cruisers, and a number of destroyers sortie and head to the southwest toward the Mandates, which was the expected axis of any IJN attack on Hawaii which is the opposite direction from the actual IJN line of approach putting them out of range for the IJN aircraft.
Scenario 2. Good result U.S. 4 hours warning, no information on IJN position. Ships are able to set Condition One, Nevada, several cruisers (1 CA, 3-4 CL) 15-20 DD sortie and move toward Mandates. Army AAA 2/3 manned and with 50% or less ammo. ~40% of fighters get up at least partly armed. IJN first wave attack is disrupted, but not stopped completely. Attacks on airbases are only partly successful. Second wave finds Army AAA at 100% ships fully ready. IJN aircraft losses 10%, mission kill 20%-30% (105-140 aircraft). U.S. loses 100+ aircraft in air or on ground. Most BB take some damage, with at least one being a total loss (Oklahoma is a good bet, she's out board and has the worst internal compartmenting of the outboard ships).
Scenario 3. Draw 2 Hours warning, no information on IJN location. Most ships are at Condition One, Army AAA less than half manned with limited ammo, 20-30 fighters get up. Shipping losses are close to OTL, but with less damage to California & West Virginia thanks to less flooding but IJN aircraft losses are 10%, 15-20% mission kill (88 aircraft, 35 aircrew).
Scenario 4. OTL significant IJN tactical victory.
Scenario 5. Less favorable U.S. result U.S. 7-8 Hours notice of the attack, accurate information on the position of the Kido Butai. Aircraft are on Dawn Patrol, probably close to a full squadron. Three BB and some escorts head toward IJN and are caught in deep water with less than 15 fighters as CAP. All BB lost, at least one cruiser, all in deep water. Japanese force that continues to Pearl is savaged as in Scenario 1. American casualties are 3,000+.
Scenario 6 Strategic U.S. Defeat 12 Hours notice of the attack, accurate information on the position of the Kido Butai. Aircraft are on Dawn Patrol, probably close to a full squadron. Entire battle line heads out to engage IJN. Caught in open water by both IJN waves at edge of Fighter Cover. Five BB lost, two damaged in open water. Pearl facilities not struck, USAAF losses minimal. Japanese losses are under 30 aircraft. U.S. casualties 4,000+
Scenario 6 Utter U.S. Defeat 18 Hours notice of the attack, accurate information on the position of the Kido Butai. As in # 6 except Lexington TF moves into position to intercept. Lexington has 16 F2A Buffaloes for CAP/Raid escort against 6 Japanese carriers. Lexington lost, probably with one or two of CA escorts.
A couple notes:
The BB at Pearl had not received their planned 1940's upgrades (Colorado was not at Pearl because she was getting this major upgrade which included addition of 5"/38 DP guns). They had a 4 76mm AAA and some 1.1" pom-poms along with .50 cal machine guns for anti-aircraft. In port, tied up, they could put up a reasonable amount of small caliber flak into a small area. At sea, at normal formation spacing, they were almost helpless, something the the Navy had recognized from the early battle in the North Atlantic and was one of the main goals of the planned modernization.
The AAA at Pearl was fairly dense, for the time. It was totally inadequate for the attack at hand, especially in heavy flak. The 76MM guns topped out at 20k feet, something that was know to the IJN, with most of the remaining AAA being 20mm and .50 cal. It is likely that, in ideal conditions, the AAA would have taken down more no more than 10% of the enemy aircraft in each wave, with 5% being a much more likely (and quite good) outcome, with a similar number mission killed and pushed over the side when they returned to the carriers.
The Fleet was not up to handling the Kido Butai at sea, anything that creates that sort of engagement is a disaster. Although he wouldn't have done it, Kimmel's best play was to run to the southwest, collecting the Enterprise Group as he went. The USN was at least a solid year from having a surface force that could defend itself from a serious air attack, even with a carrier in support.