RBC Capital’s Mike Abramsky has raised his fourth quarter iPhone and iPad estimates based on the results of a survey of 2,200 potential buyers. The survey, conducted in August by ChangeWave research, showed what Abramsky called “unprecedented iPhone 5 demand and strong back-to-school iPad buying intentions.”

In a note to clients issued Tuesday he ticked off the main data points: (I quote)

• 31% of those surveyed said they were very/somewhat likely to buy the iPhone 5, significantly exceeding pre-launch iPhone 4 demand (25%)
• With the iPhone 4 nearly 15 months old, 66% of existing iPhone users are very/somewhat likely to buy the iPhone 5, pointing to a large pending upgrade cycle.
• 54% of surveyed Sprint subscribers and 53% of surveyed T-Mobile subscribers say they are significantly/somewhat more likely to buy the iPhone, if available.
• Survey data also shows strong iPad 2 back-to-school buying indications, with 26% very/somewhat likely to buy the iPad 2. ChangeWave survey data shows 85% of all tablet buyers plan to buy the iPad, up from 82% in February.

Based on these results, Abramsky has raised his fourth quarter iPad estimate to 12.5 million units (from 10.5 million) and his first quarter 2012 iPhone estimate to 27 million units (from 24.4 million). His Q4 2011 iPhone estimate remains unchanged at 19.5 million.

Below: A ChangeWave chart of tablet-buying intentions that should strike fear in the hearts of Apple’s (AAPL) competitors.