Piper Jaffray’s Gene Munster this afternoon writes that data from research firm NPD for sales of Apple‘s (AAPL) Mac computers in the U.S. are showing a decline of 7%, year over year, for the first two months of the September- ending fiscal Q4, which he thinks is “in line” with his, and the Street’s , estimate for a 5% year-over-year increase in global Mac sales for the quarter. Munster thinks the data are a slightly “negative” surprise for investors, but he also notes that Apple has outperformed NPD data by a wide margin the last two quarters: We have analyzed domestic NPD retail data for the first two months of the September quarter (month of July and August). Combined, the data suggests NPD Mac sales are tracking down 7% y/y. Thus Mac sales remain weak, as they have been since the beginning of 2012. We believe the reading may be a small surprise to investors, but the focus for Apple has shifted more and more to iPhone and iPad, which represent the majority of the business. We note that for both the March and June quarters, Apple-reported Mac growth outpaced NPD by 12 percentage points (NPD -5% y/y vs actual up 7% y/y in March and - 10% vs up 2% in June). For September, we remain comfortable with our up 5% y /y estimate, which implies 5.1 million Macs.