How readily do potential migrants respond to increased returns to migration? Even if origin areas become less attractive vis-à-vis migration destinations, fixed costs can prevent increased migration. We examine migration responses to hurricanes, which reduce the attractiveness of origin locations. Restricted-access U.S. Census data allows precise migration measures and analysis of more migrant-origin countries. Hurricanes increase U.S. immigration, with the effect increasing in the size of prior migrant stocks. Large migrant networks reduce fixed costs by facilitating legal immigration from hurricane-affected source countries. Hurricane-induced immigration can be fully accounted for by new legal permanent residents (“green card” holders).