The Round Goby (Neogobius melanostomus) is a small, benthic fish species, native to the Black and Caspian Seas that has proliferated in non-native waterbodies in Europe and North America, making it one of the most globally significant invasive species and causing a suite of ecological changes (Kornis et al. 2012; Gallardo and Aldridge 2020; Lower et al. 2024). Since introduced into the Laurentian Great Lakes in the 1990s, Round Goby has spread rapidly, reaching the Hudson River Estuary, NY in 2021. However, their downstream expansion potential into saline environments from this North American coastal invasion front is currently unknown. To address invasion risk, we experimentally assessed the salinity tolerance of Round Goby; adult Round Gobies were subjected to weekly salinity increases of 3 parts per thousand (ppt), concluding at 33ppt, and monitored for behavior and color changes, and mortality. Tolerance trials were run at three temperatures: preferred temperature of 20°C, 26°C reflective of summer conditions, and 5°C reflective of winter conditions. We found significant salinity tolerance differences dependent on water temperature, with the highest tolerance at 5°C and the lowest tolerance at 26°C. By 30ppt, survival was 87% at 5°C and only 7% at 26°C. Temperature-dependent salinity tolerance findings suggest Round Goby expansion potential into high salinity habitats may be seasonally dependent, with expansion opportunities occurring in colder months and expansion barriers occurring in warmer months. To assess longer term survival and body condition, another experiment maintained Round Gobies at four sustained salinities (≤ 21ppt) for ten weeks at 20°C. Growth and hepatosomatic index at 21ppt were significantly lower (p<0.001) than at 1, 9, and 15ppt, indicating sustained exposure to higher salinities may affect energy stores, potentially limiting establishment potential. The salinity tolerance trial results were then applied to the Hudson River watershed by using them as inputs for a model that predicts survival rate of Round Goby at any given temperature and salinity combination. Using historic datasets of benthic temperature and salinity layers in GIS, we mapped seasonal predicted Round Goby survival for one month throughout the Hudson River Estuary, New York-New Jersey Harbor Estuary, and Long Island Sound. We found the entirety of the Hudson River Estuary to be at high risk (≥90% survival for one month) of Round Goby invasion year-round. Lower portions of New York Harbor and eastern portions of Long Island Sound have lower invasion risk in summer and fall (1-60%). However, in winter and spring, monthly survival probability exceeds 90% throughout most of the study area. Our maps are useful to managers in need of evaluating the risk of future Round Goby expansion throughout the Hudson River Estuary and connected waterways. Additional future studies aiming at assessing reproductive capabilities and other life stage survival across salinity levels will be important for informing expected establishment of Round Goby, not just survival, in brackish and marine habitats.