Three successive storms will surge in from the Pacific Ocean this week, forecasters said Tuesday, bringing what may be the most rain in nine months to drought-stricken Northern California and offering a promising start to winter after two years marked by record wildfires and dry conditions.

Two of those storms look like atmospheric rivers — narrow, moisture-rich storms that play a critical role in the state’s water supply. The first, which was set to arrive late Tuesday night and continue into Wednesday morning, is likely to be a moderate storm. But another big one shaping up for Sunday night was upgraded to a category 5 on Tuesday, the highest in a five-level scale.