We’re at the midway point of the season, which means it’s a good time to check in on the progress of each organization’s top prospect entering the season. Today we’ll go through the National League, then hit on the American League clubs next week.

Arizona Diamondbacks, RHP Jarrod Parker: After a quick whip through the high Class A California League, Parker moved up to Double-A Mobile, where he has shown a fastball that can sit 92-96 mph with a plus slider and the makings of a potentially above-average changeup. A line drive off his wrist slowed the 20-year-old Parker down a bit, but he’s on pace to be one of the youngest pitchers in the big leagues by 2010. 

Atlanta Braves, RHP Tommy Hanson: The most dominant pitcher in the Triple-A International League to start the season, Hanson finally got the call to the big leagues in June. In six starts, Hanson has a 2.25 ERA, though his 23-18 K-BB mark is nothing special. The strikeouts have been low and the walks have been high, but based on his track record, his fastball and a pair of yo-yo breaking balls, Hanson should start adding more strikeouts to his resume soon.

Chicago Cubs, 3B Josh Vitters: The third overall pick in 2008, Vitters opened the year in low Class A, but the 19-year-old annihilated the Midwest League before his recent callup to the high Class A Florida State League. Vitters hit .316/.351/.535 in 70 games with Peoria and clocked 15 home runs. Whether he can replicate that success at higher levels remains to be seen; he doesn’t strike out at a high clip, but he has an aggressive approach that led to just eight walks before his promotion.

Cincinnati Reds, 1B Yonder Alonso: After Alonso made a promising debut in his first full pro season, a broken right hamate bone last month will keep him out of the lineup until August at the earliest. When healthy, Alonso showed advanced pitch recognition, power and the ability to use the whole field at high Class A Sarasota and Double-A Carolina.

Colorado Rockies, CF Dexter Fowler: Fowler has mostly been treading water as Colorado’s starting center fielder with a .252/.348/.382 line in 77 games. But as a 23-year-old in the big leagues with excellent athleticism and a broad range of average to above-average tools, Fowler could still develop into an above-average player in the near future.

Florida Marlins, CF Cameron Maybin: In 26 big league games, Maybin looked lost. Then again, Maybin is just 22 years old, had no Triple-A experience and only brief stints in the big leagues last year with Florida and preivously with Detroit. The Marlins bumped Maybin back down to Triple-A New Orleans, where the results have been completely different. In 46 games with the Zephyrs, Maybin is batting .341/.429/.494 with 22 walks and 30 strikeouts.

Houston Astros, C Jason Castro: It’s always hard to know what to make of players in the launching pad of Lancaster. Castro hit .309/.399/.517 in 56 games in the high Class A California League, and since then has batted .284/.316/.378 in 20 Double-A games. He’s still one of the better catching prospects in the minor leagues with a good approach at the plate and above-average power, though how he plays in Double-A will tell us more than his Lancaster performance.

Los Angeles Dodgers, LF Andrew Lambo: At only 20 years old, Lambo opened the season in Double-A Chattanooga, impressive for a 2007 fourth-round pick. At 6-foot-3, 190 pounds, the lefty-hitting Lambo has been more steady than spectacular, hitting .276/.332/.444 in 81 games. He’s not particularly athletic and is a well below-average runner, so his bat will have to carry him to be a big league regular.

Milwaukee Brewers, SS Alcides Escobar: Escobar could probably step into the lineup tomorrow in Milwaukee and immediately become one of the best defensive shortstops in the big leagues. His hitting improved last year in Double-A, and he’s showing that he can still handle the bat enough for a shortstop in Triple-A Nashville, where he’s hitting .299/.350/.423 in 85 games with 23 walks, 55 strikeouts and 29 steals in 36 attempts. In most organizations, Escobar would already be in the big leagues.

New York Mets, LF Fernando Martinez: After mashing his way through the Triple-A International League, Martinez made his major league debut in May at 20 years old. Martinez scuffled in his brief big league time before coming down an injury—a regular staple in Martinez’s career—this time with knee problems.

Philadelphia Phillies, RF Dominic Brown: What more could you ask for from a right fielder? Brown can hit for average, has the patience to draw walks, is tapping into his power potential from his 6-foot-5, 204-pound frame and plays above-average defense with his speed and 70 arm. As a 21-year-old, Brown is hitting .299/.379/.540 in 51 games in the high Class A Florida State League, though a broken finger has kept him out the last month.

Pittsburgh Pirates, 3B Pedro Alvarez: The underlying tools are still there, but Alvarez’s performance hasn’t lived up to expectations since the Pirates made him the second pick in last year’s draft. Alvarez has some patience to get on base and outstanding raw power (he has 17 home runs and a .240 isolated power) but he’s had trouble making contact and has looked confused against lefthanded pitching.

St. Louis Cardinals, 3B Brett Wallace: The Cardinals have pushed their prospects aggressively through their system, which is why their first-round pick from a year ago is already in Triple-A. Between Double-A and Triple-A this year, Wallace has continued to prove that he can hit and hit for power, with an advanced approach and a balanced swing.

San Diego Padres, 1B Kyle Blanks: Through the years Blanks has had his doubters, but the Padres’ top prospect entering the season has just continued to rake. Blanks, who we’re obligated by law to mention is 6-foot-6, 285 pounds, hit .283/.393/.485 in 66 games with Triple-A Portland before getting called up to San Diego in June. The Padres have experimented with Blanks in left field, though scouts think he’s a better fit at first base.

San Francisco Giants, LHP Madison Bumgarner: At some point in his career, Bumgarner is going to finish the year with an ERA above 2.00. But it didn’t happen last year in his pro debut, and it might not happen this year either. Between high Class A San Jose and Double-A Connecticut, the 19-year-old Bumgarner has a 1.66 ERA in 81 1/3 innings with just 20 walks and 68 strikeouts. While most 19-year-old pitching prospects are learning in low Class A, Bumgarner is pushing for a big league promotion.

Washington Nationals, RHP Jordan Zimmermann: It’s somewhat faint praise, but Zimmermann has been the second-best pitcher on the Nationals’ major league staff this year. Zimmerman mixes a low- to mid-90s fastball with a plus slider in the mid-80s, as well as a high-70s changeup at times. His 4.52 ERA in 79 2/3 innings isn’t flashy, but his 78 strikeouts (8.8 per nine innings) and 25 walks (2.8 per nine) are auspicious signs.