Born in Siquirres, Costa Rica, Alvarado started his academy career at Santos de Guápiles before moving to Saprissa.

In December 2009, AZ Alkmaar signed the Costa Rican goalkeeper from Deportivo Saprissa, the youngster moved to the Netherlands in July 2010.

But after Romeo's injury from his international duty,[5] Alvarado made his AZ debut on 12 February 2011 against PSV Eindhoven, where it turned out to be disastrous when he conceded four goals, in a 4–0 loss.

"[7] From that on, Alvarado continued to be the first choice goalkeeper temporary, where he made six appearances for the club in the 2010–11 season, including a clean-sheet in a match against Heerenveen on 19 February 2011.

[7] Alvarado became a first choice goalkeeper for AZ after Sergio Romero's departure to Sampdoria and Joey Didulica's unexpected retirement.

[14] The KNVB subsequently rescinded the red card, and Ajax banned Wesley van W from all of their home matches for life.

He would also have to undergo treatment for an alcohol problem and report to police during all Eredivisie and Dutch national team matches.

[21] In both games against Anzhi Makhackala in the play-offs, Alvarado was in goal, as they proved to be too strong and failed to win either legs losing 1–0 and 5–0 respectively.

[28] Alvarado was the ever present goalkeeper, making thirty-four appearances, including the play-offs, which AZ lost 3–0 on aggregate against Groningen.

With his contract expiring at the end of the 2014–15 season, Alvarado was expected to leave the club, with newly signed Sergio Rochet from Uruguay as his successor.

[40] In March 2014, he ruled out a selection for the 2014 FIFA World Cup due to an apparent strife with national team manager Jorge Luis Pinto.

[44] In the CONCACAF Gold Cup, Alvarado was included in the squad and replaced Keylor Navas as a first choice goalkeeper following his injury.

[48] While growing up in Costa Rica, Alvarado made good friends with Joel Campbell, having played together in childhood.