Surveys of auto executives and analysts by Bloomberg and Reuters show that the US Seasonally Adjusted Annual Selling Rate (SAAR) hit 13m units last month, a 16 percent increase compared to April 2010. And though the market is up significantly from last year, it’s looking like April’s sales will be basically flat from last month. But the effects of the Japanese quake and tsunami are only just beginning to be felt in the US market…

Edmunds chief analyst Jessica Caldwell reckons

As inventories rapidly deteriorate, April could be the last month that we’ll see strong sales numbers until late summer or early fall. May and June are traditionally high-volume months, and with anticipated supply constraints — especially on fuel-efficient vehicles that have been in higher demand with spiked gas prices — inventories will be exhausted further

Though the Detroit automakers and Hyundai are likely to try to steal some of the volume that the Japanese brands will inevitably lose over the coming months, analysts are suggesting that the real gains could be in pricing rather than sheer volume. GM and Chrysler, in particular, are thought to face greater challenges in capturing market share due to rising gas prices and their relatively less-efficient lineups, while Ford and Hyundai are seen as more likely to be the volume winners as the Japanese automakers start to deal with potentially devastating inventory shortages. Check back tomorrow for complete April sales reporting.